An Integrated Framework for Treatment and 

Management of Produced Water 

TECHNICAL ASSESSMENT OF PRODUCED WATER TREATMENT 

TECHNOLOGIES 

1st EDITION 

RPSEA Project 07122-12 

November 2009 
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1st Edition 

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TECHNICAL ASSESSMENT OF PRODUCED WATER TREATMENT 

TECHNOLOGIES 

This report presents a comprehensive literature review and technical assessment to 

evaluate existing and emerging technologies that have been used for treatment of produced water 

or novel technologies that could be tested and considered in the future. This technical assessment 

includes stand-alone water treatment processes, hybrid configurations, and commercial packages 

developed for treatment of oil and gas produced water and zero liquid discharge (ZLD). This 

assessment considers pretreatment, desalination, post-treatment, and concentrated waste disposal 

to meet the required water quality standards for beneficial use scenarios. It should be noted that 

many commercially available products for produced water treatment are usually unique 

combinations of unit processes. This document focuses on primary unit processes, and attempts 

to include the major commercial packages/processes for produced water treatment. This 

document can be used to evaluate various treatment processes in a generic fashion even if their 

vendors are not listed in the report. 

The report was developed as part of a collaborative research project (#07122-12) led by 

the Colorado School of Mines (CSM) and funded by the Research Partnership to Secure Energy 

for America (RPSEA). 

TECHNOLOGIES ASSESSED 

A total of 54 technologies were reviewed and assessed in the study. The technologies are 

classified into stand-alone technologies and combined treatment processes. 

Stand-alone/primary Multi-technology processes 

Basic Separation 

o Biological aerated filters 

o Hydroclone

o Flotation

o Settling

o Media filtration

Membrane Separation 

o High pressure membranes

 Seawater RO

 Brackish water RO

 Nanofiltration (NF)

 VSEP

o Electrochemical charge driven membranes

 Electrodialysis (ED), ED reversal (EDR)

 Electrodionization (EDI)

o Microfiltration/ultrafiltration

 Ceramic

 Polymeric

o Thermally driven membrane

 Membrane distillation (MD) 

o Osmotically driven membrane

 Forward osmosis (FO)

Enhanced distillation/evaporation 

o GE: MVC

o Aquatech: MVC

o Aqua-Pure: MVR

o 212 Resources: MVR 

o Intevras: EVRAS evaporation units

o AGV Technologies: Wiped Film Rotating 

Disk

o Total Separation Solutions: SPR – Pyros

Enhanced recovery pressure driven 

o Dual RO w/ chemical precipitation

o Dual RO w/HEROTM: High Eff. RO

o Dual RO w/ SPARRO

o Dual pass NF

o FO/RO Hybrid System

Commercial treatment RO-based processes 

o CDM

o Veolia: OPUSTM

o Eco-Sphere: OzonixTM

o GeoPure Water Technologies
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Thermal Technologies 

o Freeze-Thaw

o Vapor Compression (VC)

o Multi effect distillation (MED)

o MED-VC

o Multi stage flash (MSF)

o Dewvaporation

Adsorption 

o Adsorption

o Ion Exchange

Oxidation/Disinfection 

o Ultraviolet Disinfection

o Oxidation

Miscellaneous Processes 

o Evaporation

o Infiltration ponds

o Constructed wetlands

o Wind aided intensified evaporation

o Aquifer recharge injection device (ARID)

o SAR adjustment

o Antiscalant for oil and gas produced water

o Capacitive deionization (CDI) & Electronic 

Water Purifier (EWP) 

o Gas hydrates

o Sal-ProcTM, ROSP, and SEPCON

Commercial Treatment IX-based processes 

o EMIT: Higgins Loop

o Drake: Continuous selective IX process

Eco-Tech: Recoflo® compressed-bed IX 

process

o Catalyx/RGBL IX
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EVALUATION CRITERIA 

This review broadly documents state-of-the-art research and development efforts in 

produced water treatment. The technologies and configurations identified in the review are 

technically assessed in terms of several important criteria, which are summarized in Table 1. 

The technologies are evaluated based on water quality bins: (i) feed water quality, and 

particularly salinity and constituents of concern for treatment processes (e.g., hydrocarbons, 

suspended solids, hardness, silica, barium, iron, manganese, boron); (ii) product water quality 

and its relation to water quality requirements for different produced water discharge regulations 

and beneficial use applications, including surface water discharge, agriculture irrigation, life 

stock irrigation, and USEPA drinking water standards. Another key criterion in the technical 

assessment is production efficiency in terms of product water recovery, which is directly related 

to waste (liquid or solids) generated on site that has to be disposed offsite. Other key criteria 

included power requirements, chemicals used, enclosure and footprint, reliability, robustness, 

costs, O&M considerations, pretreatment and post treatment requirements, and concentrate 

management options. The applicability of the technology in produced water treatment is 

qualitatively scored from poor to excellent. The ranking is based on: 

 Poor - the technology can not be used to treat CBM produced water 

 Moderate - there are significant hurdles, but under certain circumstances the technology 

may be appropriate for treatment of CBM produced water. 

 Good – the technology has merit, but there may be some factors that limit its 

broad utilization for treatment of CBM produced water. 

 Excellent – the technology can be used for treatment of CBM produced water and is 

commercially available. The technology can be deployed in the field (with appropriate 

pretreatment or design considerations) and will perform its desired function. 

The goal of this report is to provide potential users with an objective and unbiased 

technical assessment. In addition to the description of the technology theory and key technical 

and economic considerations listed in Table 1, the report summarizes important findings from 

field trials, pilot studies, or bench scale studies. The report expands on benefits and limitations of 

each treatment technology based on previous studies. 

This report is a synthesis of published material, including peer-reviewed journal articles, 

conference presentations and proceedings, technical reports, contract reports, reviews, feasibility 

analysis, annual reports, media reports, and information posted on vender’s website and 

brochures. Although the report delimits between manufacturer claims and peer-reviewed 

scientific data through the case studies, the users should be aware that, for some 

technologies/processes, manufacturer brochures are the only available source for information. 
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Table 1. Description of assessment criteria 

Criteria Description/Rationale 

Industrial status Emerging or existing technology in which industry, whether being 

previously employed for produced water treatment and to what level 

(full-scale, pilot-scale, bench-scale), whether it is a competitive or noncompetitive vendor market (including supplier names), minimum and 

maximum plant size 

Feed water quality bins Applicable TDS range, types of water chemistry makeup, constituents 

of concerns including: hydrocarbons, suspended solids, hardness, 

boron, silica, barium, iron, manganese, etc 

Product water quality Overall reported or estimated rejection in terms of TDS, sodium, 

organic constituents, heavy metals, ammonia, and others 

Production efficiency 

(recovery) 

Specific production efficiency in terms of reported and/or estimated 

product water recovery 

Infrastructure considerations Known infrastructure constraints or considerations such as modularity, 

mobility, energy type, relative footprint, electrical supply, housing, 

brine discharge, chemical storage, etc. 

Energy consumption Types of energy needed and power requirements 

Chemicals Types of chemicals required for process control (such as for 

regeneration, fouling, scaling, alkalinity, corrosion, and disinfection) 

and cleaning 

Life cycle Expected life of the process and replacement needs 

O&M considerations Levels of monitoring and control required, including quality control 

Level of skilled labor required 

Level of flexibility: easy to adapt to highly varying water quantity and 

quality 

Level of robustness: ability of the equipment to withstand harsh 

conditions, such as cold weather climates, shut-down and restart 

Level of reliability – little down time, need for maintenance 

Types of energy required 

Overall costs Reported treatment, capital, operation, and maintenance costs. 

Identification of major cost components including waste disposal. 

Identification of components offering most cost reduction 

opportunities 

Pre-and post treatment Types and levels of pre- and post-treatment required by the technology 

 

Concentrate management or 

waste disposal 

Waste to feed volume ratio. Concentrate treatment and/or available 

disposal options of concentrate or solid wastes. Special disposal 

considerations, if any 

Applicability in produced 

water treatment 

Qualitatively scoring the technology for the produced water 

application criterion (excellent to poor) 
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WASTE DISPOSAL COST 

Because waste disposal is a common consideration for all water treatment technologies, 

the costs of waste disposal are discussed here prior to the review of water treatment technologies. 

Waste disposal costs strongly depend on the location of and distance of the disposal facility from 

the production site, disposal method, the type of waste (quality and quantity), and the extent of 

competition in the local or regional area [1]. In 1997, Argonne National Laboratory (ANL) 

compiled data on costs charged by offsite commercial disposal companies to accept produced 

water, rain water, and other “water type wastes” [2]. In 2005, ANL began collecting current 

information to update and expand the database [1]. This section provides information about the 

new 2005–2006 database and focuses on the availability of offsite commercial disposal 

companies, the prevailing disposal methods, and estimated disposal costs. 

The categories of waste in the database include: 

• Contaminated soils 

• Naturally occurring radioactive material (NORM), 

• Oil-based muds and cuttings, 

• Produced water, 

• Tank bottoms, and 

• Water-based muds and cuttings. 

The different waste management or disposal methods in the database include: 

• Bioremediation, 

• Burial, 

• Salt cavern, 

• Discharge, 

• Evaporation, 

• Injection, 

• Land application, 

• Recycling, 

• Thermal treatment, and 

• Treatment. 

Produced water disposal costs reported in the ANL report [1] are briefly presented below. 

The reported costs are assumed to be lower than or comparable to the costs available for onsite 

management by the operators themselves. It should be noted that the types of waste are important 

to disposal costs. For example, a facility in Wyoming charges $8/bbl, for particularly dirty 

wastes that need pretreatment before injection, while the same facility charges as low as 

$0.75/bbl for cleaner wastes [3]. This implies that the disposal costs of more concentrated or 

solidified wastes after produced water treatment might be more costly than disposal of more 

diluted produced water. However, the volume of the wastes will be minimized and might result 

in reduced overall disposal costs. 

Overall disposal costs range between $0.30/bbl and $105.00/bbl depending on the 

disposal method. The higher costs are charged by a thermal treatment facility in Texas, an 

evaporation facility in Colorado, and a landfill facility in Louisiana. The lowest costs are charged 

by one cavern operator in Texas as well as several injection facilities in Oklahoma. By far, the 
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most common commercial disposal method for produced water is injection, followed by 

evaporation and burial. 

Injection of produced water on a commercial basis occurs throughout the U.S. Texas, 

Louisiana, and Oklahoma hold the most significant shares in commercial disposal well 

operations. The disposal costs range between $0.30/bbl and $10/bbl. In most cases, costs do not 

reach $1/bbl. Newpark Environmental Services in Louisiana and Texas disposes of produced 

water through solids injection. Costs range between $5/bbl and $10.50/bbl. 

Today, evaporation of produced water is most widely practiced in Wyoming (seven 

companies), followed by Colorado (four companies), Utah (four companies), and New Mexico 

(three companies). Except in one case, the disposal costs range between $0.40/bbl and $3.95/bbl. 

One company in Colorado charges $84/bbl. 

Burial in landfills is available for produced water across the nation. However, 

solidification, which is generally required, drives up the costs. Volume-based costs range 

between $3/bbl and $22/bbl in Texas and North Dakota, and $18 cubic yard ($3.75/bbl) in New 

Mexico. Weight-based costs vary significantly by state, but generally range between $15/ton and 

$80/ton. Mississippi and Louisiana report higher ranges of up to $128/ton and $250/ton, 

respectively. Burial of produced water in commercial pits is not widely reported. Three 

companies, in Oklahoma, Utah, and Wyoming, report costs ranging between $0.35/bbl and 

$4/bbl. 

Cavern disposal is a competitive option for produced water in Texas. Five companies at 

multiple facilities offer their services for a cost between $0.30/bbl and $10/bbl. 

Discharge of produced water under an NPDES permit was reported by three companies 

in Pennsylvania and one company in Wyoming. The costs range between $0.045/gal and 

$0.055/gal ($2.25/bbl and $2.75/bbl) in Pennsylvania, and between $2.50/bbl and $3.50/bbl in 

Wyoming. All four companies apply treatment prior to discharge. Two facilities in Pennsylvania 

discharge produced water to a POTW for a disposal fee of between $0.015/gal and $0.050/gal 

($0.75/bbl to $2.50/bbl). 

Land application of produced water is offered in Arkansas (one company), New Mexico 

(two companies) and Utah (one company). Costs are between $0.30/bbl and $0.40/bbl in 

Arkansas, $5.18/bbl to $18/bbl in New Mexico, and $100/ton ($26.25/bbl) in Utah. Treatment of 

produced water is offered by CCS Energy Services LLC in Alabama and Eco Mud Disposal in 

Texas. Costs range between $5/bbl and $14/bbl. Recycling of produced water is not widely 

reported. One company identified in California charges $5/bbl. Another company in Oklahoma 

indicates a cost of $25/load. Thermal treatment of produced water is offered by Clean Harbors 

Environmental Services at its Deer Park facility. Costs range between $0.02/lb and $0.20/lb 

($40/ton to $400/ton, or $10.5/bbl to $105/bbl). 
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REVIEW AND ASSESSMENT OF WATER TREATMENT TECHNOLOGIES 

The following section presents a descriptive write-up corresponding to each technology, 

based on the list of criteria included in Table 1. A detailed tabular summary, or synopsis, of the 

assessment matrix is presented to facilitate an overall assessment with respect to the evaluation 

criteria. 

Biological Aerated Filters 

The term biological aerated filter (BAF) refers to a class of technologies, including fixed 

film and attached growth processes, roughing filters, intermittent filters, packed bed media 

filters, and conventional trickling filters. A BAF consists of permeable media, such as rocks, 

gravel, or plastic media. The water to be treated flows downward over the media and over time 

generates a microbial film on the surface of the media ( 

Figure 1). The media facilitates biochemical oxidation/removal of organic constituents. 

This is an aerobic process and aerobic conditions are maintained by pumps and fans in the 

system. The thickness of the microbial layer continues to increase as the filter is used. 

Eventually, the microbial layer becomes thick enough that part of the slime layer becomes 

anaerobic and the microbial layer begins to slough off in the filter effluent [4]. Media should 

have high surface area per unit volume, be durable, and inexpensive. The type of media is often 

determined based on what materials are available at the site. Media can be field stone or gravel 

and each stone should be between one and four inches in diameter, to generate a pore space that 

does not prohibit flow through the filter and will not clog when sloughing occurs [5]. 

Figure 1. Schematic drawing of a biological aerated filter. 

BAF can remove oil, suspended solids, ammonia, and nitrogen, chemical oxygen demand 

(COD), biological oxygen demand (BOD), iron, manganese, heavy metals, soluble organics, 

trace organics, and hydrogen sulfide. Iron and manganese removal in BAFs is mainly due to 

chemical oxidation rather, not a biological process. Since BAFs do not remove dissolved 

constituents, however, high concentrations of salts can decrease the effectiveness of this 

technology due to salt toxicity effects. At chloride levels below 6,600 mg/L, there is no 

diminished contaminant removal with BAFs and at 20,000 mg/L chloride levels there will be a 

reduction in slime growth and BOD removal [6]. This technology can be used to treat water with 

much greater organic contaminant concentrations than typically found in CBM produced water. 
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BAF is a well established technology and has been used for produced water treatment for 

many years [7, 8]. Because of this technology’s ability to remove oil and grease, it has been 

primarily used for oil-field produced water treatment [7]. Informal versions of BAFs require 

minimal equipment, can be made by flowing water over rock beds. These types of BAFs have 

also been used in CBM produced water treatment for iron removal and suspended solids 

removal. 

Removal capability of BAFs is dependent on the hydraulic loading rate on the filter and 

the raw water quality. The following are approximate removal capabilities of this technology: 60 

to 90% nitrification, and 50 to 70% total nitrogen [4], 70 to 80% oil, 30 to 60% COD, 85 to 95% 

BOD, and 75 to 85% suspended solids [7]. 

There is nearly 100% water recovery from this process. The residuals generated are from 

the settling of the microbial layer that sloughs off of the media. The residuals generation, which 

is highly dependent on the water quality, is approximately 0.4 to 0.7 pounds of dry solids per 

1000 gallons of water treated (for wastewater treatment) [9]. 

Primary sedimentation should be employed upstream from BAFs to allow the full bed of 

the filter to be used for removal of non-settling, colloidal, and dissolved particles if the water 

requires a large degree of contaminant removal. Sedimentation should also follow BAFs to 

remove the microbial layer that sloughs off of the filter. Other equipment that may be used 

includes pumps and fans for aeration, and distribution nozzles. The estimated energy demand for 

BAFs is 1 to 4 kWh/day. No chemicals are necessary [5]. A summary of the BAF assessment is 

provided in Table 2. 

Table 2. Biological Aerated Filter Assessment

Criteria Description/Rationale 

Industrial status Well established technology and has been used for treatment of 

produced water [8]. Numerous vendors. 

Feed water quality bins Most effective on waters with chloride levels below 6,600 mg/L [6]. 

Oil < 60 mg/L; COD < 400 mg/L; BOD < 50 mg/L. 

* Maximum feed water concentrations depend on % removal and 

target water quality 

Product water quality 50 to 70% total nitrogen [9] 

70 to 80% oil [7] 

30 to 60% COD [7] 

85 to 95% BOD [7] 

75 to 85% suspended solids [7] 

Production efficiency 

(recovery) 

Waste from this process is removed as a solid, therefore, water 

recovery is nearly 100% 

Energy use The power requirement for BAFs is 1 to 4 kWh 

Chemicals use No chemicals are required for BAFs during normal operation, no 

cleaning is required 

Expected lifetime of critical 

components 

Long expected lifespan. Some types of BAFs consist only of rock beds 

hand holding ponds and do not require any equipment. 

Infrastructure considerations BAFs require upstream and downstream sedimentation, therefore, they 

have a large footprint and are not very mobile or modular 
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Table 2. Biological Aerated Filter Assessment

Criteria Description/Rationale 

O&M considerations Very little monitoring required 

Occasional emptying of sedimentation ponds required 

Does not require skilled operators 

Easy to adapt to highly varying water quantity and quality 

Little down time or need for maintenance 

Electricity required for pumps and fans for aeration and circulating 

water 

Overall costs The majority of the overall cost of this technology is capital. O&M 

costs are very low. 

Pretreatment of feed water Sedimentation may be required upstream of BAFs and is required 

downstream of BAFs. 

Post-treatment of product water Typically none required. 

Concentrate management or 

waste disposal 

Solids disposal is required for the sludge that accumulates in the 

sedimentation basins. Can account for up to 40% of total cost of 

technology. 

Note: 1 barrel = 42 US gallons 

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Hydrocyclone 

Hydrocyclones are used to separate solids from liquids based on the density of the 

materials to be separated. Hydrocyclones normally have a cylindrical section at the top where the 

liquid is fed tangentially and a conical base (Figure 2). The angle of the conical section 

determines the performance and separating capability of the hydrocyclone. Hydrocyclones can 

be made from metal, plastic, or ceramic and have no moving parts. The hydrocyclone has two 

exits, one at the bottom, called the underflow or reject for the more dense fraction and one, called 

the overflow or product at the top for the less dense fraction of the original stream [10]. 

Figure 2. Schematic drawing of a hydrocyclone. 

Hydrocyclones can be used to separate liquids and solids or liquids of different densities. 

Hydrocyclones can be used to remove particulates and oil from produced water. Depending on 

the model of hydrocyclone employed, they can remove particles in the range of 5 to 15 μm [11]. 

Hydrocyclones will not remove soluble oil and grease components [12]. 

Hydrocyclones have been used extensively to treat produced water and are marketed by 

numerous companies for produced water treatment [13, 14]. Hydrocyclones were used to treat 

fracturing brine in the Barnett Shale play [15]. In this research study, hydrocyclones were used in 

combination with organo-clays as a pretreatment to reverse osmosis. 

Hydrocyclones do not require any pre- or post-treatment. They do not require any 

chemicals or energy. The hydrocyclone is the only piece of equipment necessary. There are no 

energy requirements unless the plant setup requires a forwarding pump to deliver water to the 

hydrocyclone. Depending on the size and configuration of the hydrocyclone, a large pressure 

drop can occur across the hydrocyclone. 

The waste generated from a hydrocyclone is slurry of concentrated solids. This is the 

only residual that requires disposal. A summary of the hydrocyclone assessment is provided in 

Table 3. 
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Table 3. Hydrocyclone Assessment

Criteria Description/Rationale 

Industrial Status Hydrocyclones have been widely used for produced water. They are 

mainly used for oil/water separation and can also be used for 

particulate removal. 

Feed water quality bins Applicable to all TDS bins, independent of salt type and concentration. 

High organic concentrations. 

High oil and grease or high particulate concentrations. 

Product water quality Can reduce oil and grease concentrations to 10 ppm. 

Production efficiency 

(recovery) 

High product water recovery. 

Energy use The hydrocyclone does not require energy unless a forwarding pump is 

necessary to deliver water to the hydrocyclone or to recover pressure 

lost through the hydrocyclone. 

Chemicals use None. 

Expected lifetime of critical 

components 

Long, no moving parts, may suffer from abrasion. 

Infrastructure considerations Minimal. 

Forwarding pump may be required to pressurize feed stream. 

O&M considerations Solids can block inlet and scale formation can occur requiring 

cleaning, however, typical cleaning is minimal. 

Overall costs Contact vendor. 

Pretreatment of feed water None required. 

Post treatment of product water This process is usually used as part of a treatment train. Post treatment 

may be required to remove other constituents from feed water. 

Concentrate management or 

waste disposal 

Disposal required for slurry. 

Note: 1 barrel = 42 US gallons 

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Flotation 

Flotation is a process in which fine gas bubbles are used to separate small, suspended 

particles that are difficult to separate by settling or sedimentation (Figure 3). Gas is injected into 

the water to be treated and particulates and oil droplets suspended in the water are attached to the 

air bubbles and they both rise to the surface. As a result, foam develops on the surface, which is 

commonly removed by skimming. The dissolved gas can be air, nitrogen, or another type of inert 

gas. Dissolved air/gas flotation can also be used to remove volatile organics and oil and grease. 

Dissolved air flotation units have been widely used for treatment of produced water [16-18]. 

Gas flotation technology is subdivided into dissolved gas flotation (DGF) and induced 

gas flotation (IGF). The two technologies differ by the method used to generate gas bubbles and 

the resultant bubble sizes. In DGF units, gas (usually air) is fed into the flotation chamber, which 

is filled with a fully saturated solution. Inside the chamber, the gas is released by applying a 

vacuum or by creating a rapid pressure drop. IGF technology uses mechanical shear or propellers 

to create bubbles that are introduced into the bottom of the flotation chamber [14]. Coagulation 

can be used as a pretreatment to flotation.

The efficiency of the flotation process depends on the density differences of liquid and 

contaminants to be removed. It also depends on the oil droplet size and temperature. Minimizing 

gas bubble size and achieving an even gas bubble distribution are critical to removal efficiency 

[16]. Flotation works well in cold temperatures and can be used for waters with both high and 

low TOC concentrations. It is excellent for removing natural organic matter (NOM). Dissolved 

air flotation (DAF) can remove particles as small as 25m. If coagulation is added as 

pretreatment, DAF can remove contaminants 3 to 5 m in size [11]. In one reported study, 

flotation achieved an oil removal of 93% [19]. Flotation cannot removal soluble oil constituents 

from water. Treatment costs are estimated to be $0.60/m3 [18]. 

Figure 3. Flotation unit (Source: [20]). 

Because flotation involves dissolving a gas into the water stream, flotation works best at 

low temperatures. If high temperatures are present, a higher pressure is required to dissolve the 

gas in the water. A summary of the flotation assessment is provided in Table 4. 
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Table 4. Flotation Assessment.

Criteria Description/Rationale 

Industrial Status Widely used for produced water treatment, primarily for conventional 

oil and gas produced water [16-18] 

Feed water quality bins High TOC, oil and grease, particulates < 7% solids [21] 

Not ideal for high temperature feed streams 

Product water quality 93% oil removal [19] 

75% COD removal [21]; 90% removal of H2S [21] 

Production efficiency 

(recovery) 

High recovery, nearly 100% 

Infrastructure considerations Dissolved air flotation requires an external pressurized tank 

Energy consumption Energy is required to pressurize the system to dissolve gas in the feed 

stream. 

Chemicals use Coagulant chemical may be added to enhance removal of target 

contaminants. 

Expected lifetime of critical 

components 

No information available. 

O&M considerations Chemical coagulant and pumping costs are the major components of 

O&M costs for flotation. 

Capital and O&M costs No information available. Contact vendor. 

Pretreatment of feed water Coagulation may be used as a pretreatment for flotation 

Post treatment of product water No post treatment required. 

Concentrate management or 

waste disposal 

Solids disposal will be required for the sludge generated from 

flotation. 

Note: 1 barrel = 42 US gallons 

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Adsorption 

Adsorption can be accomplished using a variety of materials, including zeolites, 

organoclays, activated alumina, and activated carbon. Chemicals are not required for normal 

operation of adsorptive processes. Chemicals may be used to regenerate media when all active 

sites are occupied. Periodically the media is backwashed to remove large particulates trapped 

between the voids in the media. Typically, these processes can be gravity fed and do not require 

an energy supply, except during backwash. 

Adsorbents are capable of removing iron, manganese, total organic carbon, BTEX 

compounds, heavy metals, and oil from produced water. Adsorption is generally utilized as a unit 

process in a treatment train rather than as a stand-alone process. The adsorbent can be easily 

overloaded with large concentrations of organics, so this process is best used as a polishing step 

rather than as a primary treatment process [14]. 

Media usage rate is one of the main operational costs for adsorptive processes. When all 

active site of the adsorptive material have been consumed, the material must either be 

regenerated or disposed of. Regenerating the materials will result in a liquid waste for disposal. 

Solid waste disposal is necessary when the material needs to be replaced entirely. A summary of 

the adsorption assessment is provided in Table 5. 

Table 5. Adsorption Assessment

Criteria Description/Rationale 

Industrial status Adsorption is commonly used for treatment of produced water 

Feed water quality bins Applicable to all TDS bins, independent of salt type and concentration. 

Can remove iron, manganese, TOC, BTEX, and oil. 

Zeolites can also be used to exchange calcium for sodium to reduce 

SAR

Product water quality > 80% removal of heavy metals [22] 

Production efficiency 

(recovery) 

Nearly 100% product water recovery. 

Energy use Minimal. 

Chemicals use Chemicals may be required for media regeneration. 

Expected lifetime of critical 

components 

Media may require frequent replacement or regeneration depending on 

media type and feed water quality. 

Infrastructure considerations Adsorption processes require a vessel to contain the media and pumps 

and plumbing to implement backwashes. 

O&M considerations There will be a pressure loss incurred across the filter, however, 

depending on the plant configuration; this may not require any 

additional pumps. Pumps will be necessary to backwash the filters. 

Capital and O&M costs None available. 

Pre and post treatment Adsorption is best used as a polishing step to avoid rapid usage of 

adsorbent material. 

Concentrate management or 

waste disposal 

Waste disposal is required for spent media or the waste produced 

during regeneration of the media. 

Note: 1 barrel = 42 US gallons 

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Media filtration 

Filtration can be accomplished using a variety of different types of media: walnut shell, 

sand, anthracite, and others. Filtration is a widely used technology for produced water, especially 

walnut shell filters for the removal of oil and grease. There are many vendors available that 

market filtration technologies specifically for produced water. 

Filtration does not remove dissolved ions and performance of filters is not affected by 

high salt concentrations, therefore filtration can be used for all TDS bins regardless of salt type. 

Filtration can be used to remove oil and grease and TOC from produced water. Removal 

efficiencies can be improved by employing coagulation upstream from the filter. A summary of 

technical assessment on media filtration is provided in Table 6. 

Table 6. Filtration Assessment

Criteria Description/Rationale 

Industrial status Filtration has been used extensively for produced water treatment. 

Multiple vendors available that market filtration technologies 

specifically for produced water treatment. 

Feed water quality bins Applicable to all TDS bins, independent of salt type and concentration. 

Product water quality > 90% oil and grease removal 

Production efficiency 

(recovery) 

Nearly 100% water recovery is achieved with filtration; some filtrate 

may be used for backwashes. 

Energy consumption Minimal energy is required for these processes. Energy is required for 

backwashing the filter. 

Chemicals use Coagulant may be added to the feed water to increase particle size and 

enhance separation. Chemicals may be required for media 

regeneration. 

Expected lifetime of critical 

components 

Media may require frequent replacement or regeneration depending on 

media type and feed water quality. 

Infrastructure considerations Filtration processes require a vessel to contain the media and pumps 

and plumbing to implement backwashes. 

O&M considerations There will be a pressure loss incurred across the filter, however, 

depending on plant configuration; this may not require any additional 

pumps. Pumps will be necessary to backwash the filters. 

Capital and O&M costs Contact vendor. 

Pre and post treatment None. 

Concentrate management or 

waste disposal 

Solid waste disposal is required for spent media or the waste produced 

during regeneration of the media. 

Note: 1 barrel = 42 US gallons 

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Oxidation 

Chemical oxidation treatment can be used to remove iron, manganese, sulfur, color, 

tastes, odor, and synthetic organic chemicals. Chemical oxidation relies on oxidation/reduction 

reactions, which consist of two half-reactions: the oxidation reaction in which a substance loses 

or donates electrons, and a reduction reaction in which a substance accepts or gains electrons. 

Oxidation and reduction reactions will always occur together since free electrons cannot exist in 

solution and electrons must be conserved [23]. Oxidants commonly used in water treatment 

applications include chlorine, chlorine dioxide, permanganate, oxygen, and ozone. The 

appropriate oxidant for a given application depends on many factors including raw water quality, 

specific contaminants present in the water, and local chemical and power costs [23]. Chemical 

oxidation is well established, reliable, and requires minimal equipment [24]. Oxidation can be 

employed to remove organics and some inorganic compounds like iron and manganese from 

produced water. The removal or oxidation rate may be controlled by applied chemical dose and 

contact time between oxidants and water. 

No pretreatment is required for oxidation. Solid separation post-treatment might be 

required to remove oxidized particles. Chemical metering pumps are required for dosing. Some 

equipment may be required to generate the oxidant on-site. Chemical costs may be high. A 

summary of the oxidation assessment is provided in Table 7. 

Table 7. Oxidation Assessment 

Criteria Description/Rationale 

Industrial status Chemical oxidation is well established, reliable, and requires 

minimal equipment. Used to remove COD, BOD, organic, and some 

inorganic compounds like iron and manganese. 

Feed water quality bins Applicable to all TDS bins, independent of salt type and 

concentration. 

Product water quality Depends on type of oxidant used 

Production efficiency (recovery) 100% recovery. 

Infrastructure considerations Chemical metering equipment is required. 

Energy consumption Energy usage usually accounts for approximately 18% of the total 

O&M for oxidation processes. 

Chemicals Chemical costs may be high.

Life cycle Critical components of the oxidation process are the chemical 

metering pumps. Chemical metering equipment can have a life 

expectancy of 10 years or greater. 

O&M considerations Periodic calibration and maintenance of chemical meter pumps is 

required. 

Overall costs Capital costs can be near to $0.01/gpd, O&M costs can be 

approximately $0.05/kgal (>$0.01/bbl) 

Pre-and post treatment No pretreatment or post-treatment is required for oxidation. 

Concentrate management or waste 

disposal 

No waste is generated from oxidation processes. 

Note: 1 barrel = 42 US gallons 

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Settling 

Settling can be achieved using a pond or a basin. In this process, particulates are removed 

by gravity settling. Settling ponds require a large footprint and environmental mitigation to 

protect wildlife. Settling ponds will most likely be used in combination with other treatment 

processes. There are no chemical requirements but chemicals can be used to enhance 

sedimentation. Infrastructure requirements include liners. Settling ponds are used to remove 

large particulates from water sources. The degree of particle removal and size of particles 

removed depends on the water detention time in the pond. A summary of the settling processes 

assessment is provided in Table 8. 

Table 8. Settling Assessment. 

Criteria Description/Rationale 

Industrial status Settling is frequently employed for produced water at the full scale. 

Feed water quality bins There are no feed water restrictions to using settling as a treatment 

technology. 

Product water quality Depends on system design 

Production efficiency 

(recovery) 

Water volume may be lost due to evaporation depending on the 

residence time and configuration of the settling basin. 

Infrastructure considerations A large footprint is required for settling. The volume required depends 

on the hydraulic residence time required for the desired level of 

contaminant removal. 

Energy consumption None, unless pumping is required to get water to or from the settling 

basin. 

Chemicals No chemicals are required. 

Life cycle Long lifespan. 

O&M considerations Minimal. 

Overall costs Not available 

Pre-and post treatment No pretreatment required. Any necessary post treatment will be 

determined by the feed water quality and the target product water 

quality. Settling may be used as a unit process in a larger treatment train. 

Concentrate management or 

waste disposal 

The material that settles out of the feed water will require disposal. 

Note: 1 barrel = 42 US gallons 

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Ultraviolet Disinfection 

UV radiation disinfection is a popular form of primary disinfection because of its ease of 

use, no need of chemicals, and no formation of disinfection byproduct (DBP). Water is pumped 

through a UV reactor, which is equipped with an array of UV lamps providing disinfection 

dosages of 30-50 mJ/cm2

. As pathogens path through the reactor they are inactivated. They are 

exposed to the UV light for a predetermined period of time, depending on the desired level of 

disinfection. UV reactors are typically closed channel for potable water treatment and are 

installed in open channel for wastewater treatment. There are several types of UV lamps, with 

low pressure-high output (LPHO) and medium-pressure (MP) mercury vapor lamps being the 

most commonly used [24]. The lamps are housed inside of quartz lamp sleeves in the reactor to 

protect the lamp from breaking. 

The mechanism of UV disinfection is inactivation through UV damage of the 

microorganism’s DNA and/or RNA. Removal of suspended solids from the feedwater to UV is 

important to avoid shielding of microorganisms from the UV by suspended solids. This 

phenomenon is called “shadow effect”. UV disinfection does not provide a disinfectant residual. 

Therefore, addition of chlorine or chloramine as a secondary disinfectant might be required [24]. 

Disinfection is typically the last treatment step in most water treatment facilities, most 

suspended solids and/or dissolved ions, if any, should have been removed prior to disinfection. 

No waste is generated in UV disinfection. UV equipment including lamps must be properly 

checked to ensure they are working according to technical specifications. The lamps age with 

time and require periodic replacement. A cleaning system must also be installed on the lamp 

sleeves, because the sleeve itself reacts with compounds in water and would decrease the UV 

transmittance if they are not cleaned [24]. A summary of the UV radiation assessment is 

provided in Table 9. 

Table 9. Ultraviolet Disinfection. 

Criteria Description/Rationale 

Industrial status Not widely used for produced water treatment. May be best applied 

as a polishing step for produced water after other treatment 

processes. 

Feed water quality bins Applicable to all TDS bins. May not be suitable for highly turbid 

water. 

Product water quality Inactivation of microbial contaminants. 90 to 99% inactivation 

efficiency depending on UV intensity. 

Production efficiency (recovery) 100% water recovery. 

Infrastructure considerations UV requires a treatment chamber or area in which the water will be 

“dosed” with UV exposure. 

Energy consumption 3-25 kWh; 0.5-3 kW/mgd for LPHO 

Chemicals None. 

Life cycle Lamp life is approximately 5,000 to 8,000 hours. 

O&M considerations Minimal operator involvement, approximately 5 hours per month. 

Periodic cleaning and lamp replacement is required. 

Overall costs High capital cost. EPA estimated costs are $0.13/gpd. 
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Table 9. Ultraviolet Disinfection. 

Criteria Description/Rationale 

Pre-and post treatment Will require pretreatment to remove high concentrations of 

particulates, manganese, calcium, iron, and magnesium, which may 

decrease the effectiveness of the UV. No post treatment required. 

Concentrate management or waste 

disposal 

None. 

Note: 1 barrel = 42 US gallons 

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Microfiltration/Ultrafiltration 

Microfiltration (MF) has the largest pore size (0.1-3 m) of the wide variety of 

membrane filtration systems. Ultrafiltration (UF) pore sizes range from 0.01 to 0.1 m. In terms 

of pore size, MF fills in the gap between ultrafiltration and granular media filtration. In terms of 

characteristic particle size, MF range covers the lower portion of the conventional clays and the 

upper half of the range for humic acids. This is smaller than the size range for bacteria, algae, 

and cysts, and larger than that of viruses. MF is also typically used for turbidity reduction, 

removal of suspended solids, Giardia, and Cryptosporidium. UF membranes are used to remove 

viruses, color, odor, and some colloidal natural organic matter [25]. Both processes require low 

trans-membrane pressure (1-30 psi) to operate, and both are now used as a pretreatment to 

desalination technologies such as reverse osmosis, nanofiltration, and electrodialysis, but cannot 

remove salt themselves [24]. 

MF membranes can operate in either cross-flow separation as shown in Figure 4 and also 

dead-end filtration where there is no concentrate flow. There are also two pump configurations, 

either pressure driven or vacuum-type systems. Pressure driven membranes are housed in a 

pressure vessel and the flow is fed from a pump. Vacuum-type systems are membranes 

submerged in non-pressurized tanks and product water is extracted by a vacuum pump on the 

product side. Typical recoveries can range from 85% to 95% [23]. Flux rates range from 20 to 

100 gpd/ft2

 (gfd) depending on the application. Backwash is usually used to clean the 

membranes and it is carried out for short durations (3 to 180 seconds) in relatively frequent 

intervals (5 min to several-hour) [23]. The frequency and duration of backwash depend on the 

specific application. A clean in place (CIP) can also be performed as a periodic major cleaning 

technique. Typical cleaning agents are sodium hypochlorite, citric acid, caustic soda, and 

detergents. They can be initiated manually, and automatically controlled. CIP is initiated when 

backwashing and chemically enhanced backwash are not effective in restoring desirable 

performance [24]. 

Figure 4. Dead-end filtration versus cross-flow filtration (Source: [26]). 
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Factors affecting membrane selection are: 

 Cost 

 Percent recovery 

 Percent rejection 

 Raw water characteristics 

 Pretreatment 

Factors affecting performance are: 

 Raw water characteristics 

 Pressure 

 Temperature 

 Regular monitoring and maintenance 

A self-backwashing 100 m strainer is often necessary to protect the membranes and 

moderate particulate loading. Depending on the raw water quality, a coagulant may be added to 

form pin-sized floc and help improve rejection [24]. 

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Ceramic MF/UF membrane 

Ceramic ultrafiltration and microfiltration membranes are made from oxides, nitrides, or 

carbides of metals such as aluminum, titanium, or zirconium [27]. Ceramic membranes are much 

more resilient than polymeric membranes and are mechanically strong, chemically and thermally 

stable, and can achieve high flux rates. Typically, a tubular configuration is used with an insideout flow path, where the feed water flows inside the membrane channels and permeates through 

the support structure to the outside of the module. These membranes are typically comprised of 

at least two layers, a porous support layer and a separating layer, see Figure 5 [28]. 

Figure 5. SEM micrographs of ceramic membrane (a) SEM of membrane support and membrane 

separating layer (100x), (b) SEM of membrane support (1000x), and (c) SEM of membrane 

separating layer (5000x). 

Ceramic membranes are capable of removing particulates, organic matter, oil and grease, 

and metal oxides. Ceramic membranes alone cannot remove dissolved ions and dissolved 

organics. Pre-coagulation, injection of a chemical coagulant upstream from the membrane, 

improves removal efficiencies of dissolved organic carbon and smaller particulates. As with 

conventional ultrafiltration and microfiltration, a strainer or cartridge filter is necessary as 

pretreatment for ceramic membranes. 

Numerous research studies have been conducted on using ceramic membranes to treat 

oil-containing wastewater and produced water [29-33]. These research studies have shown that 

ceramic membranes perform better than polymeric membranes on oil-containing waters. 

Ceramic membranes have also been employed commercially to treat oil produced water [34]. 

Ceramic membranes are employed as part of a large treatment train consisting of multiple unit 

process at the Wellington Water Works to treat oilfield produced water. 

Energy requirements for ceramic membranes are lower than those required for polymeric 

membranes. Infrastructure requirements for ceramic membranes are similar to other membrane 

processes and include a break tank for the feed water, a feed pump, a rack for holding the 

membrane modules, a chemical metering system if necessary, a tank for the filtrate water and a 

pump and valves for the backwash and cleaning systems. 

Ceramic membranes have a higher capital cost than polymeric membranes. The use of 

ceramic membranes is increasing as more research and pilot studies are conducted. The capital 

cost of ceramic membranes will continue to decrease as they become a more widely used 

technology. Ceramic membranes do require frequent backwashes; backwash waste will require 

disposal. If ceramic membranes are operated in a cross-flow mode, then there will be a residual 

process stream to dispose of. An assessment of ceramic MF/UF membranes is provided in Table 

10. 

(a) (b) (c)
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Table 10. Ceramic MF/UF Membrane Assessment 

Criteria Description/Rationale 

Industrial status Ceramic membranes have been used extensively in industrial water 

treatment, including oil-containing wastewaters. Ceramic membranes 

are currently being used in a full-scale facility in Wellington, Colorado 

to treat oilfield produced water [34]. 

Many research studies have been performed which show that ceramic 

membrane are a viable treatment for produced water [29-33]. 

Many companies manufacture and sell ceramic membrane products in 

a variety of sizes, materials of construction, and geometric 

configurations. 

Feed water quality bins Applicable to all TDS bins, independent of salt type and concentration. 

High iron concentrations can be problematic, causing irreversible 

membrane fouling. 

Product water quality Product water is free of suspended solids. DOC removal is 

approximately 10%. Nearly all non-dissolved organic carbon removed. 

Production efficiency 

(recovery) 

Ceramic MF/UF membranes can be operated in dead-end or crossflow 

filtration mode, therefore, recoveries can range from 90% to 100%. 

Infrastructure considerations A feed tank, feed pump, coagulant dosing pump, and rack structure for 

holding the membrane modules is required for installation of a ceramic 

membrane plant. 

Energy consumption Not available. 

Chemicals Pre-coagulation may be used to enhance contaminant recovery. Doses 

usually range from 1 to 5 mg/L depending on water quality and the 

type of coagulant used. Common coagulants include polyaluminum 

chloride, ferric chloride, and aluminum sulfate. 

Chemical enhanced backwash may be used which would require the 

use of acidic and alkaline chemicals. 

Periodic chemical cleaning is required. Acids, bases, surfactants, and 

oxidants are commonly used. 

Life cycle Ceramic membranes are believed to have a lifespan much longer than 

polymeric membranes. Expected lifespan is >10 years. 

O&M considerations Ceramic membranes should be backwashed periodically and chemical 

cleaning is required at one week to a 3-month intervals depending on 

the feed water quality. 

Overall costs No capital or O&M costs are available at this time for ceramic 

membranes. Contact vendor for more information. 

Pre-and post treatment Straining or cartridge filtration is required as pretreatment to ceramic 

membrane systems. Coagulation can also be used as a pretreatment. 

Downstream processes may be required for desalination or polishing 

depending on feed water quality and finished water quality goals. 

Concentrate management or 

waste disposal 

Backwash waste requires disposal or recycling to a different part of the 

treatment plant. Chemical waste is generated during periodic 

cleanings. If the membranes are operated in crossflow mode, then the 

reject stream will require disposal or further treatment. 

Note: 1 barrel = 42 US gallons 

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Polymeric MF/UF membrane 

Polymeric MF/UF membranes are made from materials like polyacrylonitrile (PAN) and 

polyvinylidene (PVDF). Because there is a large market for polymeric ultrafiltration membranes, 

there are many vendors and suppliers for these membranes. They are also relatively inexpensive. 

Typically, package systems are purchased and installed by the vendor. 

An important consideration for polymeric MF/UF membranes is integrity testing to 

ensure that the membrane is not damaged and is operating properly. Typically, the filtrate 

turbidity is monitored to give a rough indication of membrane integrity. Membrane integrity can 

be tested through a pressure decay test. In this test, pressurized air is applied to the membranes at 

a pressure less than would cause the air to flow through the membrane, and the pressure decay is 

measured. Regular monitoring of membrane performance is necessary to ensure the membrane 

system is operating at the most effective loading rate and backwash regime. Membrane life is 

typically estimated at 7+ years with manufacturer warranties covering 5 years in municipal 

applications. 

Waste includes pretreatment waste, backwash flow, retentate flow (if applicable), and 

CIP waste. Waste streams are either discharged to the sewer or treated if discharging to surface 

waters. Waste streams being discharged to surface waters are typically processed for turbidity 

removal through settling ponds or other treatment systems. CIP waste is neutralized and usually 

combined with the rest of the waste. A summary assessment of polymeric MF/UF membranes is 

provided in Table 11. 

Table 11. Polymeric MF/UF Membrane Assessment 

Criteria Description/Rationale 

Industrial status Polymeric membranes are used extensively in the municipal water 

treatment industry. 

Feed water quality bins Applicable to all TDS bins, independent of salt type and concentration. 

Product water quality Product water is free of suspended solids. DOC removal is 

approximately 10%. Nearly all non-dissolved organic carbon removed. 

Production efficiency 

(recovery) 

85% to 100% depending on feed water quality and mode of operation 

(dead-end vs. crossflow). 

Infrastructure considerations A feed tank, feed pump, coagulant dosing pump, and rack structure for 

holding the membrane modules are required. 

Energy consumption Not available. 

Chemicals Pre-coagulation may be used to enhance contaminant recovery. Doses 

usually range from 1 to 5 mg/L depending on water quality and the 

type of coagulant used. Common coagulants include polyaluminum 

chloride, ferric chloride, and aluminum sulfate. 

Chemical enhanced backwash may be used which would require the 

use of acidic and alkaline chemicals. 

Periodic chemical cleaning is required. Acids, bases, surfactants, and 

oxidants are commonly used. 

Life cycle 7 years or longer. 

O&M considerations Integrity monitoring is required. 

Overall costs Capital cost for polymeric ultrafiltration systems vary based on the size 

of the plant and feed water quality. Approximate capital costs will be 

near $1 - $2/gpd ($0.02 to $0.05/bpd) and O&M costs approximately 

$1 to $2/kgal ($0.02 to $0.05/bbl). 
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Table 11. Polymeric MF/UF Membrane Assessment 

Criteria Description/Rationale 

Pre-and post treatment Straining or cartridge filtration is required as pretreatment to ceramic 

membrane systems. Coagulation can also be used as a pretreatment. 

Downstream processes may be required for desalination or polishing 

depending on feed water quality and finished water quality goals. 

Concentrate management or 

waste disposal 

Backwash waste requires disposal or recycling to a different part of the 

treatment plant. Chemical waste is generated during periodic 

cleanings. If the membranes are operated in crossflow mode, then the 

reject stream will require disposal or further treatment. 

Note: 1 barrel = 42 US gallons 

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REVIEW AND ASSESSMENT OF DESALINAITON TECHNOLOGIES 

Pressure Driven Membrane Technologies 

Pressure driven membrane processes utilize hydraulic pressure to overcome the osmotic 

pressure of the feed solution and force pure water (called permeate) to diffuse through a dense, 

non-porous membrane [35]. The residual feed stream (sometimes called retentate, concentrate, or 

reject) is concentrated during the process and typically requires disposal. An illustration of the 

process is shown in Figure 6. Additional treatment technologies may be employed to further 

concentrate the concentrate stream towards zero liquid discharge (ZLD). Solutions of higher total 

dissolved solids (TDS) concentrations have greater osmotic pressures, and therefore require more 

hydraulic pressure to produce permeate. Practical limits are imposed on the process by pump 

energy and component manufacturing costs associated with operating at hydraulic pressures 

exceeding 1,000 psig. For this reason, pressure driven membrane processes are typically utilized 

for treatment of saline streams with TDS concentrations ranging from 500 to 40,000 mg/L; 

however, this technology has been utilized to treat water with 50,000 mg/L TDS [36]. 

Figure 6. Schematic of a typical pressure driven membrane process. The concentrate stream may 

be further undergo additional desalination processes to produce more permeate and further 

concentrate this stream. 

High-pressure membranes are typically employed in spiral-wound configurations ( 

Figure 7) with membrane materials composed of an asymmetric polyamide or 

polypiperazine amid active layer and a polysulfone micro-porous support in a thin film 

composite (TFC) structure ( 

Figure 7). Mesh spacers are installed in both the feed channel and permeate collection 

channels of the membrane module. Feed spacers are required to enhance hydrodynamic 

turbulences in the channel, which diminishes concentration polarization. Concentration 

polarization is a phenomenon where the feed solution becomes more concentrated at the feedmembrane interface, which results from the preferential diffusion of pure water through the 

membrane. A permeate spacer is required to provide mechanical support to the permeate 

collection channel. 

Reverse osmosis (RO) and nanofiltration (NF) are examples of pressure driven 

membrane processes. RO and NF are proven, widely utilized treatment technologies for 

desalination of both seawater and brackish water [37]. Globally, RO seawater desalination 

technologies dominate global seawater desalination with a 58% share of the market and growing 

[38]. 

FEED PERMEATE

CONCENTRATE
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Figure 7. RO membrane construction. (a) A typical spiral wound high pressure membrane 

element and (b) SEM cross section view of an asymmetric RO membrane. 

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a) 

b) 
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Seawater Reverse Osmosis 

Seawater RO (SWRO) membrane systems are most applicable for feed streams up to 

47,000 mg/L TDS, i.e., seawater level % [37]. SWRO typically employs dense, highly selective 

TFC membranes that are capable of rejecting contaminants as small as 0.0001 μm. Systems that 

utilize SWRO may achieve high rejection of monovalent and multivalent ions and molecules, 

and metals. SWRO membranes are designed to achieve NaCl rejections in excess of 99% [37]. 

Other inorganic compounds such as silica and boron are rejected to a lesser extent and frequently 

require additional treatment considerations (such as increasing the pH of the RO feed stream to 

pH 10 or above). Rejection of organic compounds in SWRO ranges from very high rejections 

(greater than 99.7%) to very low rejections (<20%) depending on the organic compound’s 

chemical structure and feed solution physicochemical parameters [39]. Because of the high 

molecular weight of radionuclides, the removal of these compounds is higher than 99%. Water 

recovery during SWRO is frequently restricted to 30-60% because of limitations resulting from 

the relatively high osmotic pressure of the feed stream [40, 41]. 

Membrane fouling and scaling is a primary concern when operating RO systems. SWRO 

frequently requires pretreatment to remove organic foulants, and may require the addition of 

scale inhibitors to condition feed water prior to contact with the membranes. Constituents of 

primary concern for all pressure driven membrane processes include organic acids, metal oxides, 

and sparingly soluble salts (e.g. CaSO4, CaF2, and BaSO4). When appropriate design 

considerations are employed, SWRO systems are capable of operating with moderate chemical, 

energy, and maintenance demands. 

The utilization of energy recovery devices to recycle hydraulic pressure within the RO 

system can substantially reduce energy costs. RO processes also easily automated and are 

relatively simple to operate. SWRO is a moderately robust technology that consistently delivers 

permeate water devoid of most inorganic constituents. RO membrane systems may be deployed 

on a trailer-mounted skid, as shown in 

Figure 8, which is highly mobile and modular. SWRO technology has one of the smallest 

footprints of all the technologies considered in this report. Depending on the chemical 

composition of the RO feed water, system failure may occur with changing feed water quality. 

Low recoveries associated with SWRO generate relatively large volumes of concentrated reject 

water. Residual management costs may be substantial. 

RO systems have been previously employed for various types of produced water 

treatment. Early pilot studies were conducted without consideration for adequate pretreatment; 

subsequently the RO membranes were irreversibly damaged by foulants [42, 43]. Later, systems 

with rigorous pretreatment trains were employed with RO as a final desalination stage. One 

study was conducted at an oil field produced water facility in Bakersfield, CA (2001). The feed 

water was characterized as an NaCl dominated. The pilot system was constructed with a 100 m 

pre-filter leading to a polymeric UF membrane and followed by NF and RO. The system was 

operated for six months and produced 20 gpm of permeate over a period of more than 1,700 

hours of operation [44]. Another early study was conducted in the Placerita Canyon Oil Field, 

CA in 2000; however, little detail is available on the specifics of testing conditions and system 

configuration [45]. Recently, numerous companies with water treatment expertise have begun 

developing high-pressure membrane based treatment systems. Many of these systems will be 

discussed in the hybrid membrane systems and commercial technologies sections of this report. 

A summary of the technical assessment for SWRO is listed in Table 12. 
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Figure 8. Trailer mounted membrane testing skid used at AQWATEC, CSM (Source: [46]). 

 

Table 12. Summary of technical assessment of SWRO. 

Criteria Description/Rationale 

Status of technology Mature and robust technology for seawater desalination. Has been 

employed for produced water treatment. Reports from various 

producers in the CBM produced water field indicate that many RO 

pilot studies failed, but this is largely the result of insufficient process 

integration and poor pretreatment. 

Feed water quality bins Most applicable for TDS ranging from 20,000 to 47,000 mg/L, and 

water containing monovalent (Na, Cl), divalent (Mg, Ca, Ba, SO4), 

multi-valent (Fe*, Mn*) electrolytes, and radionuclides. Also 

applicable for specific classes of organic compounds 

Product water quality SWRO permeate quality is dependent on feed water salinity and 

operating conditions. Typically, product water TDS ranges from 100 to 

400 mg/L (>99.4% rejection), ammonia rejection is approximately 

80%, boron rejection is typically less than 50% when operating at 

neutral pH. 

Recovery Product water recovery is between 30% and 60%. 

Energy use With energy recovery device, SWRO requires 11-16 kWh/kgal (0.46-

0.67 kWh/bbl) of energy to power the system’s high-pressure pumps 

[47]. 

Chemical use Scale inhibitor and caustic may be required for process control to 

prevent scaling or fouling. Chemical cleaning rates depend on feed 

water quality. Cleaning will typically occur after certain design 

specifications are exceeded, and may require the use of NaOH, 

Na4EDTA, HCl, Na2S2O4, or H3PO4

Expected lifetime of critical 

components 

Depending on operating conditions, SWRO membranes will require 

replacement within 3 to 7 years 

Infrastructure considerations SWRO requires minimal operational footprints compared to thermal 

desalination technologies, and can be highly automated 

SWRO skids are highly mobile. 
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Table 12. Summary of technical assessment of SWRO. 

Criteria Description/Rationale 

O&M considerations Monitoring and control required for feed pH, flow rates, TDS, 

turbidity, as well as vessel pressures. 

System automation lessens demands on skilled labor, however a 

skilled technician is required to perform routine system maintenance. 

Level of flexibility: High sensitivity to organic and inorganic 

constituents in the feed water. 

Level of robustness: TFC membranes have high pH tolerance, but 

cannot be exposed to feed temperatures in excess of 113 °F (45 °C) 

Level of reliability: SWRO systems operate semi-continuously with 

automated, short duration chemical rinse or osmotic backwashing 

cycles. 

Types of energy required: electrical. 

Capital and O&M costs Capital costs vary from $3 to $7/gpd (or $125 to $295/bpd), depending 

on various factors including size, materials of construction and site 

location. Operating costs are highly dependent upon energy price and 

feed water TDS, and approximately $2/kgal (or $0.08/bbl). 

Pretreatment of feed water All high-pressure membrane technologies require extensive 

pretreatment to mitigate harmful water quality constituents that will 

otherwise foul or scale the membrane. Particular attention should be 

given to hydrophobic organic compounds and sparingly soluble salts. 

The silt density index (SDI) of the feed stream should not exceed 3-5. 

Post-treatment of product water Product water may require pH stabilization or remineralization. This 

may be achieved by lime bed contacting or by blending small amounts 

of filtered and sterilized feedwater with permeate. 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. Due to the relatively low 

recovery rates of 30% to 60%, moderately large amounts of 

concentrated brine are generated. SWRO operations are commonly 

located near oceans, which allows them to dispose of the brine by 

pumping it back into the ocean through diffusers. 

Applicability for produced 

water treatment 

Excellent - with appropriate pretreatment technologies 

Note: 1 barrel = 42 US gallon 

 (*): Assuming that ion is in a reduced (un-oxidized) state 

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Brackish Water Reverse Osmosis 

BWRO membranes are designed to achieve moderately high rejection of dissolved 

constituents (>94% NaCl), and are most efficient when employed for the treatment of feed water 

containing TDS concentrations between 500 and 25,000 mg/L. BWRO generally may achieve 

water recoveries up to 85%. BWRO membranes generally reject metals and divalent ions to a 

high degree, and have similar limitations as SWRO for organics removal. Pretreatment for 

BWRO is similar to SWRO, and requires careful management to control organic fouling and 

inorganic scaling. 

Operational costs for BWRO are reduced compared to SWRO because the hydraulic 

pressure required to overcome the osmotic pressure of the feed water is lower, and fewer 

membranes are required to achieve similar production rates. BWRO systems are equally matched 

with SWRO systems when other parameters are considered, including robustness, reliability, 

flexibility, mobility, modularity, and footprint. The higher recovery of BWRO over SWRO 

reduces concentrated brine generation and disposal costs. 

Available scientific literature suggests that BWRO membranes have been previously 

tested on CBM produced water at the bench-scale [48, 49]. One study [48] examined the 

potential of harvesting iodide from produced water, and performed other experiments to 

determine the fouling potential and effective cleaning protocols for BWRO and NF membranes. 

Seven different membranes (four BWRO membranes, and three NF membranes) were 

investigated in the study. Feed water was obtained from a natural gas production facility in 

Eastern Montana and was characterized as brackish groundwater (5,200 mg/L TDS) dominated 

by NaCl. 

A second bench-scale study [49] was conducted with both CBM produced water (sourced 

from Walsenburg, Colorado) and oil produced water (sourced from Wellington, Colorado). The 

purpose of this study was to determine the relative effectiveness of BWRO and NF membranes 

for treatment of produced water. Three membranes were tested in the investigation, one BWRO, 

and two NF membranes. The CBM produced water had 650 mg/L TDS and was dominated by 

sodium (no anion composition was given). A summary of the technical assessment for BWRO is 

listed in Table 13. 

Table 13. Summary of technical assessment of BWRO 

Criteria Description/Rationale 

Status of technology Mature and robust technology for brackish desalination in the 

municipal water treatment sector. Laboratory scale studies have been 

conducted for oil and gas produced water. 

Feed water quality bins Most applicable for TDS ranging from 500 to 25,000 mg/L, and water 

containing monovalent (Na, Cl), divalent (Mg, Ca, Ba, SO4), 

multivalent electrolytes (Fe, Mn), and radionuclides. Also applicable 

for specific classes of organic compounds. 

Product water quality BWRO permeate quality is dependent on feed water salinity and 

operating conditions. Typically, product water TDS ranges from 100 to 

1,500 mg/L, ammonia rejection may range from 60% to 80%. 

Recovery Product water recovery is between 60% and 85%. 

Energy use BWRO will require less energy than equivalent SWRO systems for a 

specific feed water quality. BWRO requires approximately 0.5 to 3 

kWh/kgal (0.02-0.13 kWh/bbl) of energy to power the system’s highpressure pumps. 
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Table 13. Summary of technical assessment of BWRO 

Criteria Description/Rationale 

Chemical use Scale inhibitor and caustic may be required for process control to 

prevent scaling or fouling. Chemical cleaning rates depend on feed 

water quality. Cleaning will typically occur after certain design 

specifications are exceeded, and may require the use of NaOH, 

Na4EDTA, HCl, Na2S2O4, or H3PO4. 

Expected lifetime of critical 

components 

Depending on operating conditions, BWRO membranes will require 

replacement within 3 to 7 years. 

Infrastructure considerations BWRO requires an equivalent footprint when compared to SWRO, and 

a minimal operational footprint compared to thermal desalination 

technologies. As with SWRO, BWRO can be automated, and mobile. 

O&M considerations Monitoring and control required for feed pH, flow rates as well as 

vessel pressures. 

System automation lessens demands on skilled labor, however a 

skilled technician is required to perform routine system maintenance. 

Level of flexibility: High sensitivity to organic and inorganic 

constituents in the feed water. 

Level of robustness: TFC membranes have high pH tolerance, but 

cannot be exposed to feed temperatures in excess of 113 °F (45 °C). 

Level of reliability: BWRO systems operate semi-continuously with 

automated, short duration chemical rinse or osmotic backwashing. 

Types of energy required: electricity. 

Capital and O&M costs Capital costs vary from $0.8 to $4/gpd (or $35 to $170/bpd), 

depending on various factors including size, materials of construction 

and site location. Operating costs are approximately $0.70/kgal (or 

$0.03/bbl). Moderate reductions in energy costs can be obtained by 

implementing energy recovery subsystems. 

Pretreatment of feed water All high-pressure membrane technologies require extensive 

pretreatment to mitigate harmful water quality constituents that will 

otherwise foul or scale the membrane. Particular attention should be 

given to hydrophobic organic compounds and sparingly soluble salts. 

The silt density index (SDI) of the feed stream should not exceed 5. 

Post-treatment of product water Product water may require pH stabilization or remineralization. This 

may be achieved by lime bed contacting or by blending small amounts 

of filtered and sterilized feed water with permeate. 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. Moderate recovery rates 

of 50% to 85% generate modest amounts of concentrated brine. 

BWRO operations are commonly located inland and the concentrated 

brine typically requires deep well injection. 

Applicability for produced 

water treatment 

Excellent - with appropriate pretreatment technologies. 

Note: 1 barrel = 42 US gallon 

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Nanofiltration 

NF membranes are commonly utilized in brackish groundwater desalination for 

municipal water supplies [37]. Some pilot-scale studies have utilized a NF membrane subsystem 

to pretreat water before treatment with RO membranes [44]. NF membranes are designed to 

reject contaminants as small as 0.001 μm. This allows NF to achieve high rejection of divalent 

ions, metals (>99% of MgSO4), and radionuclides. NF is best suited for softening applications 

and removal of most metals; this indicates that the product stream from conventional NF systems 

will tend to have higher SAR than the feed stream. Organic compounds are removed to varying 

extents with NF membranes [50]. The nominal TDS range for NF applications is between 1,000 

and 35,000 mg/L (by using two stage NF process developed at Long Beach Water Department 

[51]). Water recovery ranges from 75-90%, but may require application of scale inhibitors or 

extensive pretreatment depending on feed water quality. 

The energy required for NF membranes to perform separation is less than that required 

for SWRO or BWRO; while maintenance, robustness, reliability, flexibility, mobility, 

modularity, and operational footprint of NF membrane systems are equivalent to those of RO 

processes. 

NF membranes have been investigated on both pilot- and bench-scale for treatment of 

produced water [44, 48, 49]. The pilot-scale study [44] is discussed in the SWRO section of this 

report. Two bench-scale studies examined the treatment of CBM produced water with BWRO 

and NF membranes, and are discussed in the BWRO section of this report. A summary of the 

technical assessment for NF is listed in Table 14. 

Table 14. Summary of technical assessment of NF 

Criteria Description/Rationale 

Status of technology Mature and robust technology for water softening and metals removal 

in various sectors of the industrial and municipal water treatment 

sectors. Has been employed for produced water treatment. 

Feed water quality bins TDS applicability range is highly dependent on feed solution 

composition, but may range from 500 to 25,000 mg/L. Most useful for 

treatment of water with divalent (Mg, Ca, Ba, SO4) electrolytes, 

multivalent metals (Fe, Mn), and radionuclides. Also applicable for 

specific classes of organic compounds. 

Product water quality NF permeate quality is dependent on feed water composition and 

operating conditions. High rejection (>99%) of larger divalent ions and 

metals with moderate rejection (<90%) of monovalent salts is 

expected. 

Recovery Product water recovery is between 75% and 90%. 

Energy use NF requires less energy than equivalent RO based systems for a 

similar feed water quality. Approximately 2 kWh/kgal (0.08 kWh/bbl) 

of energy is required to power the system’s high-pressure pumps [52]. 

Chemical use Scale inhibitor and caustic may be required for process control to 

prevent scaling or fouling. Chemical cleaning rates depend on feed 

water quality. Cleaning will typically occur after certain design 

specifications are exceeded, and may require the use of NaOH, 

Na4EDTA, HCl, Na2S2O4, or H2O2. 

Expected lifetime of critical 

components 

Depending on operating conditions, NF membranes will require 

replacement within 3 to 7 years. 
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Table 14. Summary of technical assessment of NF 

Criteria Description/Rationale 

Infrastructure considerations NF requires an equivalent footprint when compared to BWRO, and a 

minimal operational footprint compared to thermal desalination 

technologies. As with other pressure driven processes, NF can be 

highly automated, and have excellent mobility. 

O&M considerations Monitoring and control required for feed pH, flow rates as well as 

vessel pressures. 

System automation lessens demands on skilled labor, however a 

skilled technician is required to perform routine system maintenance. 

Level of flexibility: High sensitivity to organic and inorganic 

constituents in the feed water. 

Level of robustness: TFC membranes have high pH tolerance, but 

cannot be exposed to feed temperatures in excess of 113 °F (45 °C). 

Level of reliability: NF systems operate semi-continuously with 

automated, short duration chemical rinse or osmotic backwashing 

cycles. 

Types of energy required: electrical. 

Capital and O&M costs Capital costs vary from $0.8 to $4/gpd (or $35 to $170/bpd), 

depending on various factors including size, materials of construction 

and site location. Operating costs are assumed similar to BWRO, 

approximately $0.70/kgal (or $0.03/bbl). Moderate reductions in 

energy costs can be obtained by implementing energy recovery 

subsystems. 

Pretreatment of feed water All high-pressure membrane technologies require extensive 

pretreatment to mitigate harmful water quality constituents that will 

otherwise foul or scale the membrane. Particular attention should be 

given to hydrophobic organic compounds and sparingly soluble salts. 

Post-treatment of product water Product water may require remineralization to restore SAR values. 

This may be achieved by lime bed contacting or by blending small 

amounts of filtered and sterilized feedwater with permeate. 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. Relatively high recovery 

rates of 75% to 90% generate minor amounts of concentrated brine. 

Applicability for produced 

water treatment 

Poor – NF is inappropriate as a standalone technology. NF processes 

will remove >99% of hardness, and will have substantially lower 

removal of Na and Cl ions, thus SAR is maximized in the product 

stream. 

Note: 1 barrel = 42 US gallon 

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Electrochemical Charge Driven Membrane Process 

Electrodialysis / Electrodialysis Reversal 

Electrodialysis (ED) and electrodialysis reversal (EDR) are electrochemical charge 

driven separation processes in which dissolved ions are separated from water through ion 

permeable membranes under the influence of an electrical potential gradient. Ion exchange 

membranes, fabricated from ion exchange polymers, have the ability to selectively transport ions 

with a positive or negative charge and reject ions of the opposite charge. An ED stack consists of 

a series of anion exchange membranes (AEM) and cation-exchange membranes (CEM) arranged 

in an alternating mode between anode and cathode (Figure 9). The positively charged cations 

migrate toward the cathode, pass the cation-exchange membrane, and rejected by the anionexchange membrane. The opposite occurs when the negatively charged anions migrate to the 

anode. This results in an alternating increasing ion concentration in one compartment 

(concentrate) and decreasing concentration in the other (diluate). The EDR process is similar to 

the ED process, except that it also uses periodic reversal of polarity to effectively reduce and 

minimize membrane scaling and fouling, thus allowing the system to operate at relatively higher 

recoveries. 

Cathode (-)

Anode (+)

Cl- Na+

Na+

Anion Exchange 

Membrane

Cation Exchange 

Membrane

Cation Exchange 

Membrane

------------

Feed + + + + + + + + + + + 

Na+

Na+

Na+

ClClClClNa+

Na+

Na+

Diluate

Concentrate

Figure 9. Schematic diagram of an ED stack. 

The efficiency of ion transfer is determined by the current density and the residence time 

of the solutions within the membrane cells. The membrane selectivity decreases with increasing 

ion concentrations. EDR and ED processes are typically used in desalination of brackish water 

(up to about 8,000 mg/L TDS for EDR) and not seawater. This is because the cost of these 

processes increases substantially with increasing salinity or TDS concentration. 

The efficiency of ED or EDR is limited by several factors such as fouling/scaling, current 

efficiency, counter effects of co-ion transport, osmosis, and diffusion. Organic fouling can occur 

in the diluate compartments due to precipitation of large negatively charged anions on the anion 

exchange membranes. Sparingly soluble inorganic salts (e.g., CaSO4, CaCO3) and multivalent 

ions (e.g., iron and manganese) can also scale the cation exchange membranes by precipitation 

and fixation. This can reduce the ED efficiency by neutralizing or reversing the fixed charges in 

the membranes. This can be avoided by pretreatment of the feedwater with processes such as 

filtration for suspended solids, softening or pH lowering, and addition of antiscalant into the 

concentrate compartments. 
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Depending on feedwater chemistry, water recovery in ED and EDR can be between 70 

and 90%. ED membranes are not as susceptible to degradation by chlorine; therefore, dosing a 

small amount of chlorine to the feed water can control biological growth in the system. These 

features enable ED and EDR to treat surface and wastewaters having high concentrations of 

organic materials and microorganisms without significant fouling. EDR system is able to operate 

with maximum silt density index (SDI) of 15 compared to 5 for RO [53, 54]. A disadvantage of 

ED and EDR is its limited removal of non-charged constituents, including organics molecules, 

silica, boron, and microorganisms. 

ED and EDR have been successfully used at a number of municipal water and wastewater 

treatment plants to desalinate brackish water and reclaimed water [55, 56]. Laboratory 

experiments have been conducted to investigate the application of ED in treatment of produced 

water at Argonne National Laboratory (ANL) and Gas Technology Institute (GTI) [56]. Moon et 

al. [57] used a laboratory ED prototype to treat CBM produced waters collected from the Powder 

River basin production field near Sheridan, Wyoming. The produced water was sodium 

bicarbonate type with TDS in the range of 1000-2000 mg/L. Preliminary results indicated water 

recovery of more than 90%. Energy consumption was in the range of 0.14 to 0.20 kWh/lb NaCl 

equivalent removed. 92% removal of dissolved solids was achieved [57]. At a scale of treatment 

exceeding 0.336 MGD (8,000 bbl/day) produced water, total costs were estimated to be below 15 

cents per barrel for a treatment train that includes 5 m cartridge filter, ED to reduce electroconductivity (EC) and sodium levels, and stabilization of the product water stream with 

limestone to increase calcium concentrations and to decrease SAR values from over 50 to below 

4 [58]. 

Sirivedhin et al. [59] tested the ability of ED to treat low- and high salinity produced 

waters at laboratory scale. Synthetic water was used to simulate produced water qualities in CO, 

TX, and WY (TDS in the range of 4,000-5,000 mg/L, sodium bicarbonate type, and sodium 

bicarbonate/sodium sulfate type waters), UT (63,000 mg/L, sodium chloride type), and OK 

(97,000 mg/L, sodium chloride type). ED treatment is more cost-effective and energy-efficient 

when treating low TDS water (e.g. TDS 4,000-5,000 mg/L). The power required to treat the high 

TDS water was approximately 23 times higher than that required to treat the low TDS water. 

While energy costs are likely to preclude using ED to treat concentrated produced water, the 

technology shows promise for treatment of relatively clean produced water such as CBM water. 

Frac Water Inc. developed mobile treatment units using patent pending High Efficiency 

ED (HEED) treatment process for treating CBM produced water and reusing it in well fracturing 

[60]. The mobile treatment units treated produced water with TDS concentrations ranging from 

11,400 to 27,000 mg/L and sulfates from 4,000 to 14,000 mg/L [61]. Pretreatment included 

cartridge filtration to remove particulate matter, carbon filters to remove organic matter, and 

weak acid cation exchange resins to remove hardness and iron. The ED treatment recovered 80-

90% of the brackish water. The HEEDTM stack configuration required up to 40% less membrane 

area that resulted in more than 70% increase in energy efficiency [62]. The product water quality 

met the requirements for the basic gel fracturing fluids. 

The drawbacks of the system are high treatment cost and membrane fouling. The 

membranes should be regularly washed or cleaned in place with dilute acid and alkali solutions 

to restore performance when required. A summary of the technical assessment of ED and EDR is 

listed in Table 15. 
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Table 15. Summary of technical assessment of ED and EDR

Criteria Description/Rationale 

Status of technology Mature and robust technology for seawater and brackish water 

desalination and wastewater reclamation. Have been tested for produced 

water treatment at laboratory-scale. 

Feed water quality bins Cost effective to TDS < 8,000 mg/L, and treat all types of water 

chemistry makeup. 

Product water quality Product water quality depends on ED stages, can achieve over 90%. 

Poor removal of non-charged substances such as organics, silica, boron, 

and microorganisms. 

Recovery Product water recovery is between 80% and >90%. 

Energy use Energy consumption was in the range of 0.14–0.20 kWh/lb NaCl 

equivalent removed [57]. 

Chemical use Scale inhibitor and acid may be required for process control to prevent 

scaling. Periodic chemical cleaning is typically conducted using acid, 

caustic, EDTA, disinfectant, or other antiscaling chemicals. 

Expected lifetime of critical 

components 

ED membrane lifetime is estimated 4-5 years. 

Infrastructure considerations No special infrastructure requirement, need housing or shed. 

O&M considerations Levels of monitoring and control: current, voltage, TDS, pH, flow rates, 

membrane integrity. 

High level of skilled labor required; the operation of ED and EDR is 

more complicated than RO membranes. 

Level of flexibility: fairly flexible to varying water quality. 

Level of robustness: modest to withstand harsh conditions. 

Level of reliable – requires periodic chemical cleaning and 

maintenance. 

Types of energy required – electricity. 

Capital and O&M costs Total costs are site specific and depend on feed water TDS. For CBM 

produced water treatment (TDS 1000 – 2000 mg/L), costs were 

estimated to be under $3.6/kgal (15 cents per barrel) for a 0.34 MGD 

(8,000 bbl/day) treatment train [58]. 

Pretreatment of feed water Pretreatment requires removal of particles and other scaling and fouling 

substances through filtration, pH adjustment, and addition of 

antiscalant. 

Post-treatment of product 

water 

Product water needs remineralization for SAR adjustment, and 

disinfection. 

Concentrate management or 

waste disposal 

Concentrate needs disposal. 

Applicability for produced 

water treatment 

 Excellent for the produced water application. 

Note: 1 barrel = 42 US gallon 

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Electrodeionization 

Electrodeionization (EDI) is a commercial desalination technology that combines ED and 

conventional IX technologies. It is used for the production of ultra-pure deionized water, 

especially in the semiconductor industry. The principle of the process is illustrated in Figure 10. 

A mixed-bed ion exchange resin or fiber is placed into the diluate cell of a conventional 

electrodialysis cell unit [63]. 

The function of the IX resins is to increase the conductivity in the substantially nonconductive water. At very low salt concentrations, the feed solution water is dissociated at the 

contact region of the cation- and anion-exchange resin beds, generating protons and hydroxyl 

ions that further replace the salt ions in the resins. The final result is completely deionized water 

as a product. The IX resins are regenerated via water splitting under current. The process can be 

performed continuously without chemical regeneration of the IX resin [63], and reduce the 

energy consumption when treating very diluted solutions [64]. 

The main disadvantage of the EDI process is the relatively poor current utilization. For 

industrial wastewater treatment, the precipitation of divalent metal hydroxide in EDI stack is a 

serious problem as a result of metal ions reacting with hydroxide ions present in the EDI stack. 

With current EDI stack configurations, EDI has not shown potential for treatment of produced 

water and beneficial use. EDI is not likely to be selected for treatment of CBM produced water 

due to high energy consumption compared to other membrane processes. 

No further assessment was conducted on EDI because of the limited information in the 

literature and its poor potential application in produced water treatment. 

Figure 10. Production of ultrapure water with EDI technology (Source: [63]). 

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Thermally Driven Membrane Process 

Membrane Distillation 

Membrane distillation (MD) is a novel thermally driven membrane separation process 

that utilizes a low-grade heat source to facilitate mass transport through a hydrophobic, 

microporous membrane. The driving force for mass transfer is a vapor pressure gradient between 

a feed solution and the distillate, and is the only membrane process that can maintain process 

performance (I.e., water flux and solute rejection) almost independently of feed solution TDS 

concentration. MD is most likely capable of producing ultra-pure water at a lower cost compared 

to conventionally distillation processes. Membrane materials commonly employed for MD 

include polytetrafluorethylene (PTFE), polypropylene (PP), and polyvinylidenedifluoride 

(PVDF). MD membranes may be packaged in either flat-sheet or hollow-fiber configurations. 

MD may be operated in four basic configurations: direct contact MD (DCMD), vacuum 

(VMD), air gap (AGMD), and sweeping gas (SGMD) [65]. Of these four configurations, DCMD 

and AGMD are the most likely to be deployed as either treatment or post-treatment for CBM 

produced water. During DCMD a warm feed stream flows on one side of the hydrophobic, 

micro-porous membrane, while a cooler aqueous solution flows counter-currently on the 

opposite side of the membrane. Molecules of water evaporate and diffuse through the pores of 

the membrane. Upon contact with the cold distillate solution on the product side of the 

membrane the vapor condenses and is assimilated into the distillate solution. AGMD works on a 

similar principle as DCMD; however, instead of a cooler distillate stream the permeate side of 

the membrane contains an air gap and a cold plate. As water vapor diffuses through the 

membrane it enters the quiescent air gap and condenses on the cold plate. A general illustration 

of the principles of DCMD and AGMD is shown in Figure 11. 

. 

Figure 11. Generalized illustration of the principles of MD. A warm feed stream containing 

various non-volatile solutes and water flow on the left side of the membrane. Water vapor 

diffuses through the membrane and condenses in a cold distillate on the right (Source: [66]). 

There is no documentation presently available that indicates that MD has been used for 

produced water treatment in the past. MD is an effective desalination technology because it is 

capable of treating feed waters with TDS concentration in excess of 35,000 mg/L. Theoretical 

rejection for all non-volatile solutes (including Na, SiO2, B, and heavy metals) is 100%; 
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however, compounds with higher volatility than water, such as BTEX and other organic 

compounds, will diffuse preferentially faster through the membrane. As a standalone process 

MD may be capable of achieving similar water recoveries as BWRO. Recovery may be 

improved to greater than 80% when coupled with crystallizer technologies to reduce scaling [67]. 

For pretreatment, MD processes require a pre-filter to screen out large particles and the 

complete removal of any surfactants present in the feed stream. If surfactants are present in the 

MD feed stream they will wet the hydrophobic pores of the MD membrane and cause pore 

flooding, which results in a substantial reduction in membrane solute rejection. Chemical 

demands for MD processes are similar to that required for pressure-driven membrane processes, 

however foulants and scale layers are more easily removed from the membrane because they are 

not physically compacted onto the membrane surface. MD requires that the feed solution 

temperature be elevated beyond that of the permeate side of the membrane; yet, a large 

temperature gradient is not required to facilitate high mass transfer. The temperature gradient can 

be as low as 20 °C [65]. The required temperature gradient may be harvested from low-grade 

waste heat generated from compressors, pumps, etc. and does not represent a significant 

operational cost. 

System maintenance is similar to that of pressure driven processes, and may require 

occasional system downtime to remove mineral scales or foulants. One benefit of MD is that the 

membranes are more chemically inert and resistant to oxidation than traditional RO and NF 

membranes, which allows for more efficient, chemically aggressive cleaning. The membrane 

module, recirculation pumps, and potentially a cooling system are the only components required 

for MD operations. The simplicity of MD process components means that they require little 

supervisory oversight. Membrane modules for MD have not undergone extensive optimization 

and may require larger footprints than a pressure driven system with equivalent capacity. 

MD is an extremely flexible technology for most variations in feed water quality and 

quantity; however, the introduction of any surfactant into the feed solution will adversely affect 

the process. As with many membrane technologies, MD modules can be readily integrated on 

mobile platforms and are highly modular. A summary of the technical assessment for MD is 

listed in Table 16. 

Table 16. Summary of technical assessment of MD 

Criteria Description/Rationale 

Status of technology Emerging thermally driven membrane technology, not previously 

employed for CBM produced water treatment. 

Feed water quality bins TDS application range is controlled by the presence of sparingly 

soluble salts. Yet, recent studies have demonstrated that scaling is not 

a major problem. Feed water TDS of 500 mg/L to greater than 50,000 

mg/L is possible, and studies have demonstrated that more than 70,000 

mg/L feed streams can be processes [68]. MD has 100% theoretical 

rejection of all non-volatile solutes. 

Product water quality MD distillate/condensate quality is equal to that of distilled water from 

thermally driven processes (TDS 2 to 10 mg/L). All solutes with 

higher volatility than water (such as ammonia) will preferentially 

diffuse into the product water. 

Recovery Product water recovery is between 60% and 95% [69]. 
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Table 16. Summary of technical assessment of MD 

Criteria Description/Rationale 

Energy use MD is a thermally driven process and therefore it requires some energy 

input. However, the process only requires a moderate temperature 

gradient to operate. This allows for the system to function by 

harvesting waste heat from other processes or onsite compressors, 

pumps, etc. 

Chemical use Scale inhibitor and caustic may be required for process control to 

prevent scaling or fouling. Chemical cleaning rates depend on feed 

water quality. Cleaning will typically occur after certain design 

specifications are exceeded, and may require the use of NaOH, 

Na4EDTA, or HCl. 

Expected lifetime of critical 

components 

Depending on operating conditions, MD membranes are likely to 

require replacement within 3 to 7 years. 

Infrastructure considerations MD processes have not enjoyed the same level of intensive research 

and development as pressure driven processes, as such the membrane 

modules are not yet optimized. This results in a larger footprint than an 

equivalent capacity RO or NF system. 

Because of its larger footprint, MD systems have reduced mobility 

when compared to pressure driven processes. 

O&M considerations Monitoring and control required for fluid temperature, flow rates, and 

membrane integrity. 

System automation lessens demands on skilled labor, however a 

skilled technician is required to perform routine system maintenance. 

Level of flexibility: High sensitivity to surfactants, hydrophobic 

organic compounds may be difficult to remove from the membrane. 

Level of robustness: MD membranes, especially PTFE based, are 

highly resistant to pH, oxidants, and irreversible flux decline. 

Level of reliability: MD systems operate semi-continuously with short 

duration chemical rinses. 

Types of energy required: electrical (if no source of waste heat is 

available). 

Capital and O&M costs Capital costs were estimated for a 1 MGD (24,000 bpd) DCMD plant 

to be $3.34/gpd (or $0.15/bpd), with operating costs estimated to be 

$1.40/kgal (or $0.06/bbl) [70]. 

Pretreatment of feed water Removal of any constituents that may wet the hydrophobic, microporous pores of the MD membrane is required for efficient process 

performance. 

Post-treatment of product water Product water may require remineralization and pH stabilization. This 

may be achieved by lime bed contacting or by blending small amounts 

of filtered and sterilized feed water with distillate/condensate. 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. High theoretical water 

recovery rates approaching 100% generate minor amounts of 

concentrated brine. 

Applicability for produced 

water treatment 

Moderate to good - Appropriate pretreatment is required to remove 

surfactants from the feed stream, and membrane modules are not yet 

optimized for water treatment in any sector. 

Note: 1 barrel = 42 US gallon 

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Osmotically Driven Membrane Processes 

Forward Osmosis 

Forward osmosis (FO) is an osmotically driven membrane process. During FO, water 

diffuses spontaneously from a stream of low osmotic pressure (the feed solution) to a hypertonic 

(draw) solution having a very high osmotic pressure. Unlike RO and NF, FO systems operate 

without the need for applying hydraulic pressure ( 

Figure 12). The membranes used for this process are dense, non-porous barriers similar 

to RO and NF membranes, but are composed of a hydrophilic, cellulose acetate active layer cast 

onto either a woven polyester mesh or a micro-porous support structure. 

Typically, the FO draw solution is composed of NaCl, but other draw solutions composed 

of NH4HCO3, sucrose, and MgCl2 have been proposed [71]. During FO the feed solution is 

concentrated while the draw solution becomes more dilute. Figure 13 illustrates a generic 

industrial scale application of FO, which requires the continuous reconcentration of the draw 

solution for sustainable system operation. One prominent method for reconcentrating the draw 

solution is to utilize an RO subsystem; this configuration will be discussed in Hybrid FO/RO 

systems. 

 

Figure 12. Water diffusion in FO and pressure driven membrane processes (RO and NF). For 

FO, ∆P is approximately zero and water diffuses to the more saline side of the membrane. For 

RO and NF, water diffuses to the less saline side due to hydraulic pressure (∆P>∆π). 

Concentrated draw 

solution recycle

Draw 

solute 

separation

Potable 

water

Diluted draw 

solution

Saline feed 

water

Brine

FO 

membrane 

unit

Figure 13. Schematic of a generic FO system for desalination. 
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FO membranes are capable of rejecting all particulate matter and almost all dissolved 

constituents (greater than 95% rejection of TDS). These attributes also allow FO to achieve very 

high theoretical recoveries while minimizing energy and chemical demands. An additional 

benefit of FO is that the process occurs spontaneously, without the need for applied hydraulic 

pressure. The hydraulic pressure applied in pressure driven membrane processes is responsible 

for compacting foulants onto the membrane, which substantially intensifies irreversible flux 

decline. Fouling layers that accumulate on FO membranes may be readily removed with cleaning 

(e.g., increasing cross-flow velocity, osmotic backwashing) or with chemicals, and irreversible 

flux decline is minimized [67, 72]. 

FO processes are capable of operating with feed TDS ranging from 500 mg/L to more 

than 35,000 mg/L, and may achieve recoveries in excess of 96% when treating brackish water 

[67]. FO membranes may be packaged in flat sheet or spiral-wound configurations. These 

packages allow for relatively small process footprints, but are still not optimized to the extent of 

pressure driven processes. 

Osmotically driven membrane processes have not yet been tested on produced waters. 

However, multiple lab scale experiments have been conducted with FO, and have utilized feed 

water supplies ranging from seawater and brackish water to municipal and industrial wastewater 

[67, 73-76]. FO has also been employed in a pilot and full-scale studies with industrial and 

municipal wastewaters, but the FO process was coupled with RO to reconcentrate the draw 

solution (see Hybrid FO/RO systems). A summary of the technical assessment for FO is listed in 

Table 17. 

Table 17. Summary of technical assessment of FO 

Criteria Description/Rationale 

Status of technology Emerging osmotically driven membrane technology. FO has not been 

previously employed for produced water treatment. 

Feed water quality bins TDS application range is controlled by the osmotic pressure 

differential between the feed solution and draw solution. The TDS 

range is between 500 mg/L to greater than 35,000 mg/L. FO has 

equivalent solute rejection performance to existing pressure driven 

processes for monovalent and divalent electrolytes, metals, and 

organics. 

Product water quality The product of FO is a diluted draw solution (typically composed of 

NaCl). To obtain pure water from the process a secondary system is 

required to extract pure water from the draw solution, and to 

reconcentrate the draw solution. This is typically accomplished with 

RO. FO membranes have similar solute rejection as NF (>90% TDS, 

>80% ammonia, low rejection of boron). 

Recovery Product water recoveries have exceeded 96% in hybrid RO/FO 

systems. 

Energy use FO is an osmotically driven process that occurs spontaneously without 

the need for substantial energy input. The process requires only 

enough power to circulate the draw solution and feed solution across 

the FO membrane. 
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Table 17. Summary of technical assessment of FO 

Criteria Description/Rationale 

Chemical use Scale inhibitor and caustic may be required for process control to 

prevent scaling or fouling. Chemical cleaning rates depend on feed 

water quality. Cleaning will typically occur after certain design 

specifications are exceeded, and may require the use of NaOH, 

Na4EDTA, or HCl. 

Expected lifetime of critical 

components 

Depending on operating conditions, FO membranes are likely to 

require replacement within 3 to 7 years. 

Infrastructure considerations FO processes have not enjoyed the same level of intensive research 

and development as pressure driven processes, as such the membrane 

modules are not yet optimized. This results in a larger footprint than an 

equivalent capacity RO or NF system. 

Because of its larger footprint, FO systems may have reduced mobility 

when compared to pressure driven processes. 

O&M considerations Monitoring and control required for flow rates and membrane 

integrity. 

System requires very little oversight, however a skilled technician is 

required to perform routine system maintenance. 

Level of flexibility: Extremely flexible technology, with sensitivity to 

low and high pH streams. 

Level of robustness: FO membranes are highly resistant to irreversible 

flux decline. 

Level of reliability: FO systems operate semi-continuously with short 

duration physical or chemical cleanings. 

Types of energy required: electrical (to power low pressure circulation 

pumps). 

Capital and O&M costs Capital costs are unknown. 

Pretreatment of feed water A prefilter is required to remove large debris; antiscalant may be 

required for high recovery operation. 

Post-treatment of product water Diluted draw solution requires further separation to produces pure 

water and reconcentrate the draw solution for reuse. 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. Relatively high recovery 

rates exceeding 96% (for hybrid RO/FO systems) generate very minor 

amounts of concentrated brine. 

Applicability for produced 

water treatment 

Moderate to good - FO may provide excellent pretreatment for 

adjacent processes, but FO membranes are not yet available for 

commercial installations. 

Note: 1 barrel = 42 US gallons 

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Hybrid Membrane Technologies 

Numerous methods have been proposed to enhance recovery and minimize concentrated 

brine volume generation resulting from membrane desalination processes. Many of these 

methods couple multiple stages of membrane-based treatment processes with intermittent 

chemical precipitation or caustic addition. These processes include: dual NF, Dual RO with 

chemical precipitation, Dual RO with softening pretreatment with high pH operation (High 

Efficiency RO (HEROTM)), and Dual RO with Slurry Precipitation and Recycling RO 

(SPARRO). Other membrane hybrid processes include novel combinations of RO with other 

established or novel membrane technologies. These include coupling FO with RO and coupling 

RO with ED. 

Dual RO with chemical precipitation 

Dual RO with chemical precipitation is a physical-chemical method for enhancing 

recovery of conventional RO processes through treatment and minimization of concentrate. The 

process employs established technologies such as lime soda softening and a second stage RO 

[77-79]. As illustrated in Figure 14, this approach is based on treatment of the concentrate from a 

primary RO system using a physical-chemical process, followed by subsequent treatment in a 

secondary RO system. The chemical treatment step utilizes precipitation to remove calcium, 

magnesium, and other sparingly soluble salts, and is followed by filtration (e.g., media filtration 

or membrane filtration) for removing solids carryover from the precipitation process. The 

secondary RO system is then operated at a higher TDS, and requires higher pressures compared 

to the primary RO system. The combined recovery of the process is reported to be 95% or 

greater for brackish water. 

Figure 14. Dual RO with intermediate chemical precipitation. 

The positive attributes of this technology include the application of established unit 

processes and relatively low additional energy requirements. Negative attributes include 

additional chemicals, production of sludge from the chemical precipitation process, and footprint 

and costs of chemical feed and storage facilities. 

This approach has recently been pilot tested at the Metropolitan Water District of 

Southern California [77]. A dual RO configuration with intermediate chemical precipitation has 

also been recently pilot tested at the Southern Nevada Water Authority [80]. This treatment 

process has not yet been utilized for CBM produced water. A summary of the technical 

assessment for a dual RO with chemical precipitation is listed in Table 18. 
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Table 18. Summary of technical assessment of dual RO with chemical precipitation

Criteria Description/Rationale 

Status of technology Pilot tested at municipal desalination plants. Not previously employed 

for CBM produced water treatment. 

Feed water quality bins TDS application range is 1,000 mg/L and 35,000 mg/L. High removals 

of monovalent and divalent ions, metals, and organics is expected. 

System is likely to achieve additional silica removal through coprecipitation. 

Product water quality Treatment process permeate quality is dependent on feed water salinity 

and operating conditions. Pilot studies report 94% rejection of TDS. 

Recovery Product water recovery is estimated to exceed 90%. 

Energy use No data is currently available. 

Chemical use Chemical demand of lime (Ca(OH)2) or caustic soda (NaOH) will 

depend on water chemistry and the quantity of calcium and magnesium 

targeted for removal. 

Chemical cleaning rates depend on feed water quality. Cleaning will 

typically occur after certain design specifications are exceeded, and 

may require the use of NaOH, Na4EDTA, or HCl. 

Expected lifetime of critical 

components 

No data is currently available. 

Infrastructure considerations This treatment process will require a substantially larger footprint that 

conventional RO systems. Chemical storage and sludge dewatering 

facilities will be required, in addition to a second bank of RO elements. 

System mobility is reduced compared to conventional RO systems. 

Filtration system and chemical storage components are the primary 

factors in limiting mobility. 

O&M considerations Monitoring and control required for flow rates, chemical dosing, and 

RO element pressure. 

System may require substantial oversight to ensure proper operation of 

the primary RO stage brine management systems. 

Level of flexibility: May have moderate sensitivity to organic and 

inorganic constituents in the feed water. 

Level of robustness: TFC membranes have high pH tolerance, but 

cannot be exposed to feed temperatures in excess of 113 °F (45 °C). 

Level of reliability: RO systems operate semi-continuously with 

automated, short duration chemical rinse or osmotic backwashing 

cycles. 

Types of energy required: electrical. 

Capital and O&M costs Costing figures are unknown. 

Pre-treatment of feed water All high-pressure membrane technologies require extensive 

pretreatment to mitigate harmful water quality constituents that will 

otherwise foul or scale the membrane. 

The feed stream to the second RO stage requires chemical precipitation 

and filtration prior to contact with the RO membranes. 

Post treatment of product water Product water may require pH stabilization or remineralization. This 

may be achieved by lime bed contacting or by blending small amounts 

of filtered and sterilized feedwater with permeate. 
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Table 18. Summary of technical assessment of dual RO with chemical precipitation

Criteria Description/Rationale 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. Relatively high recovery 

rates exceeding 90% generate very minor amounts of concentrated 

brine. 

Applicability for produced 

water treatment 

Good to excellent - the limiting criteria is chemical cost, availability, 

and disposal considerations. 

Note: 1 barrel = 42 US gallons 

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Dual RO with softening pretreatment and high pH operation (HEROTM: High Efficiency RO) 

This patented technology [81] consists of a hardness and alkalinity removal step, a 

degasification step to remove carbon dioxide, and intermediate caustic addition to increase the 

pH of the RO feed water. This technology was developed to produce water of exceptionally high 

purity for the micro-electronics industry. 

For municipal brackish water, the process combines a two-phase RO process with 

chemical pretreatment of primary RO, intermediate ion exchange treatment of primary RO 

concentrate, and high pH operation of secondary RO [82]. The approach is illustrated in Figure 

15. The (secondary) RO step operates as a “high-efficiency” system due to ion exchange 

pretreatment and high pH operation. 

The concentrate of the primary RO is treated in weakly acidic cationic (WAC) exchange

resins. The carbon dioxide from the concentrate is stripped and the pH is increased with caustic 

to above 10. This allows for the secondary RO to operate at high recoveries. Operating the 

negatively charged membranes at a high pH is reported to allow better removal of both weakly 

ionized anions as well as the strongly ionized species. The solubility of silica is increased at high 

pH, which allows for greater recovery rates when treating water that contains high concentrations 

of silica. The combined recovery of the process is estimated to be greater than 90% for brackish 

water, with typical target recovery rates of approximately 95%. 

Figure 15. Schematic of a dual RO system that incorporates a softening pretreatment and 

intermediate high pH operation (High Efficiency RO (HEROTM)). 

 

The HEROTM system has been utilized to enhance recovery of surface water (Colorado 

River water) during desalination [79]. Raw water feed characteristics included relatively low 

feed solution TDS of 950 mg/L, dominated by sodium and SO4 with the presence of other 

constituents including SiO2, B, Ca, Ba, Mg, and HCO3. Results demonstrated that recoveries of 

95% to 98% were achievable with the HEROTM system. A demonstration scale facility at the 

Arlington Valley Power Station in Arizona was constructed [83]. The facility is designed to treat 

2.4 MGD of cooling tower blow down that contains 10,000 mg/L of TDS and is saturated with 

SiO2. A summary of the technical assessment for a dual RO with chemical precipitation is listed 

in Table 19.
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Table 19. Summary of technical assessment of dual RO with softening pretreatment and 

high pH operation (High Efficiency RO (HEROTM)) 

Criteria Description/Rationale 

Status of technology Technology has undergone lab-scale testing on surface water, and 

demonstration-scale testing on cooling water blowdown. Variations of this 

process have been employed by commercial vendors for produced water 

treatment (e.g., CDM). 

Feed water quality bins The estimated TDS application range is between 500 mg/L and 10,000 

mg/L. Moderately high removals of monovalent and divalent ions, metals, 

and organics is expected. System is likely to achieve additional silica and 

boron removal with high pH operation. 

Product water quality Treatment process permeate quality is dependent on feed water salinity and 

operating conditions. Lab-scale studies report 94% rejection of TDS. 

Recovery Product water recovery is estimated to exceed 90%. 

Energy use Energy requirements are estimated to be between 11and 19 kwh/m3 (0.48 

to 0.80 kWh/bbl) 

Chemical use Chemical cleaning rates depend on feed water quality. Cleaning will 

typically occur after certain design specifications are exceeded, and may 

require the use of NaOH, Na4EDTA, or HCl. IX process will require 

regeneration with strong acid, likely H2SO4 or HCl. 

Expected lifetime of critical 

components 

No data is currently available. 

Infrastructure 

considerations 

This treatment process will require a substantially larger footprint that 

conventional RO systems. Chemical storage and sludge dewatering 

facilities will be required, in addition to a second bank of RO elements. 

System mobility is reduced compared to conventional RO systems. Lime 

softening and IX system along with chemical storage components are the 

primary factors in limiting mobility. 

O&M considerations Monitoring and control required for flow rates, chemical dosing, IX resin 

regeneration, and RO element pressure. 

System may require moderate oversight to ensure proper operation of the 

primary RO stage brine management systems. 

Level of flexibility: May have moderate sensitivity to organic and 

inorganic constituents in the feed water. IX resin requires regeneration. 

Level of robustness: TFC membranes have high pH tolerance, but cannot 

be exposed to feed temperatures in excess of 113 °F (45 °C). 

Level of reliability: RO and IX systems operate semi-continuously with 

automated, short duration chemical rinses or osmotic backwashing cycles 

(for RO). 

Types of energy required: electrical. 

Capital and O&M costs Capital costs are estimated to be $4.6/gpd ($195/bpd), while operation and 

management costs are approximated at $3.5/kgal ($0.14/bbl). 

Pre-treatment of feed water Process will require coagulation and pre-filtration to remove suspended 

solids prior to lime softening. Other pretreatment options including 

antiscalant and acid addition may be required. 

The feed stream to the second RO stage requires chemical precipitation 

and filtration prior to contact with the RO membranes. 
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Table 19. Summary of technical assessment of dual RO with softening pretreatment and 

high pH operation (High Efficiency RO (HEROTM)) 

Criteria Description/Rationale 

Post treatment of product 

water 

Product water will require pH stabilization or remineralization. This may 

be achieved by lime bed contacting or by blending small amounts of 

filtered and sterilized feedwater with permeate. 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. Relatively high recovery rates 

exceeding 90% generate very minor amounts of concentrated brine. 

Sludge from the sedimentation basin will require dewatering and landfill 

application. 

Applicability for produced 

water treatment 

Good to excellent - the limiting criteria is regenerant cost, availability, and 

disposal considerations. 

Note: 1 barrel = 42 US gallons 

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Dual RO with SPARRO: Slurry Precipitation and Recycling RO 

In SPARRO, specific crystals are added to feed water to aid in precipitation of scaling 

compounds in a membrane application. For example, Gypsum crystals are used to precipitate 

calcium sulfate. The concept of adding crystals to feed water in tubular RO membrane systems 

for preferential precipitation and the concept of recycling the seeded slurry were first patented in 

1980 [84]. 

Seed crystals are added to the water in a tubular RO membrane system and the scaling 

compounds are precipitated on the seed crystals instead of on the membrane. The seed crystals 

serve as preferential growth sites for calcium sulfate and other calcium salts and silicates, which 

begin to precipitate as their solubility products are exceeded during the concentration process 

within the membrane tubes. 

The slurry of seed crystals is recirculated in the RO system and the precipitates are 

removed from the system in a controlled fashion. Because the seed slurry is recirculated within 

the membranes, the process is confined to the use of a membrane configuration that will not 

plug, such as tubular membrane systems. 

Another patent was later awarded that focused on the methodology of determining 

adequate seed crystal concentration in the preferential precipitation systems [85]. A series of 

pilot tests were also performed by Resources Conservation Company (RCC) based on the 

original patented technology ([84, 85]. Subsequently, there have been other tests of the 

technology based on the concept of adding seed crystals to a tubular membrane configuration. 

Two variations of the further testing are discussed below. The first approach is illustrated in 

Figure 16 [86]. 

Figure 16. Schematic of Seeded Slurry Precipitation and Recycle RO (SPARRO). 

The water to be desalted is mixed with a stream of recycled concentrate containing the 

seed crystals and fed to the RO process. The concentrate with seed crystals is processed in a 

cyclone separator to separate the crystals, and the desired seed concentration is maintained in a 

reactor tank by controlling the rate of wasting the upflow and/or underflow streams from the 

separator. The combined recovery of the process is estimated to be greater than 90%. 

The positive attributes of this technology include relatively low energy costs. Negative 

attributes include requirement of tubular RO membranes, larger footprint for tubular membranes, 

and additional chemicals. This approach has been tested at pilot scale in South Africa, at the East 
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Rand Proprietary Mines [86]. A pilot testing of this approach for concentrate treatment tested at 

the Eastern Water Municipal District in California [87]. 

Another variation of the seeded slurry approach involves a two-pass process, with the 

first pass employing a tubular NF system with seeded slurry recycle and the second pass 

employing a spiral wound RO system [88]. The process was developed for an agricultural 

drainage water reclamation application and tested at bench scale. The process, known as double 

pass, preferential precipitation, reverse-osmosis process, or DP3ROTM, is proprietary and in the 

process of applying for patent. 

Although the TDS level in the agricultural drainage water is typically between 3,000 to 

12,000 mg/L, the recovery of a conventional RO system treating this water is reported to be 

limited to less than 50%, due to the high levels of calcium sulfate concentrations. The two-pass 

system is reported to be able to achieve a recovery of 92-96%. The first pass NF uses calcium 

sulfate seeds in a seeded slurry recycle configuration and provides removal of calcium sulfate 

and softening in general. The softened water is then treated with RO to meet the irrigation 

requirements (TDS < 500 mg/L and sodium adsorption ratio < 4.0). 

Other positive attributes of this technology include increased RO recovery in an 

agricultural drainage water application. Negative attributes include requirement of tubular NF 

membranes, larger footprint for tubular membranes, a two-pass system (and associated energy 

and costs), and additional chemicals. This approach has been tested at bench-scale using 

drainage water from the Panache Drainage District in California [88]. A summary of the 

technical assessment for a slurry precipitation and recycling RO system is listed in Table 20. 

Table 20. Summary of technical assessment of slurry precipitation and recycling RO 

(SPARRO).

Criteria Description/Rationale 

Industrial status Pilot-scale testing on impaired water from a mining operation. No 

previous utilization for CBM produced water treatment. 

Feed water quality bins The estimated TDS application range is between 500 mg/L and 10,000 

mg/L. Moderately high removals of monovalent and divalent ions, 

metals, and organics is expected. 

Product water quality Treatment process permeate quality is dependent on feed water salinity 

and operating conditions. Pilot-scale studies report 94% rejection of 

TDS. 

Production efficiency 

(recovery) 

Product water recovery is estimated to exceed 94%. 

Infrastructure considerations This treatment process will require a substantially larger footprint that 

conventional RO systems. Chemical storage and reaction vessel 

facilities will be required, in addition to a second bank of RO elements. 

System mobility is reduced compared to conventional RO systems. 

Energy consumption Energy requirements are estimated to at 18.2 kWh/kgal (0.77 kWh/bbl) 

Chemicals The system requires a continuous feed of seeding material. 

Chemical cleaning rates depend on feed water quality. Cleaning will 

typically occur after certain design specifications are exceeded, and 

may require the use of NaOH, Na4EDTA, or HCl. 

Life cycle No data is currently available. 
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Table 20. Summary of technical assessment of slurry precipitation and recycling RO 

(SPARRO).

Criteria Description/Rationale 

O&M considerations Monitoring and control required for flow rates, chemical dosing, and 

RO element pressure. 

System may require substantial oversight to ensure proper operation of 

integrated system. 

Level of flexibility: May have moderate sensitivity to organic and 

inorganic constituents in the feed water. 

Level of robustness: TFC membranes have high pH tolerance, but 

cannot be exposed to feed temperatures in excess of 113 °F (45 °C). 

Level of reliability: RO systems operate semi-continuously with 

automated, short duration chemical rinses or osmotic backwashing 

cycles (for RO). 

Types of energy required: electrical. 

Overall costs Capital costs are estimated to be $4.7/gpd ($199/bpd), while operation 

and management costs are currently unknown. 

Pre-and post treatment Process will require coagulation and pre-filtration to remove 

suspended solids prior contact with the slurry reaction chamber to 

ensure optimal operation. Other pretreatment options including 

antiscalant and acid addition may be required. 

Product water may require pH stabilization or remineralization. This 

may be achieved by lime bed contacting or by blending small amounts 

of filtered and sterilized feedwater with permeate. 

The feed stream to the second RO stage requires chemical precipitation 

and filtration prior to contact with the RO membranes. 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. Relatively high recovery 

rates exceeding 90% generate very minor amounts of concentrated 

brine. 

Applicability for produced 

water treatment 

Good to excellent - the limiting criteria is sludge disposal and chemical 

reagent availability. 

Note: 1 barrel = 42 US gallons 

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FO-RO Hybrid System 

During FO the feed solution is concentrated while the draw solution becomes more 

dilute. For the process to be sustainable on an industrial scale, the draw solution requires 

continuous reconcentration. One prominent method for reconcentrating the draw solution is to 

utilize an RO subsystem. Reconcentration with RO is a viable option because the draw solution 

does not contain high levels of sparingly soluble salts or foulants. Recent studies have shown that 

synergistically coupling FO with RO creates an exceptionally robust, multi-barrier system for 

treatment of highly impaired streams [69, 75, 89-91]. A system diagram is shown in 

Figure 17. 

Figure 17. Schematic drawing of a hybrid FO-RO system. Impaired feed water contacts one side 

of the forward osmosis. Water diffuses form the feed solution into the draw solution. An RO 

system is then employed to reconcentrate the draw solution and produce pure water permeate. 

Hybrid FO-RO systems have undergone pilot-scale testing at the Denver Water 

Recycling Facility with a feed source consisting of secondary and tertiary effluents [91]. Fullscale testing of a hybrid FO-RO system was completed at a landfill in the Pacific-Northwest of 

the United States [76]. During full-scale testing the system was employed to treat landfill 

leachate. Additional pilot scale testing is planned to occur in a brackish water desalination 

facility in southern California during the summer of 2010. 

The physical limit on the applicable TDS range for this process is the requirement that 

the draw solution have a higher osmotic pressure than the impaired feed water stream, and that 

the osmotic pressure of the draw solution is not prohibitive for reconcentration by RO. These 

limitations indicate that FO-RO systems are most applicable for a feed water TDS ranging from 

500 mg/L to 35,000 mg/L. An FO-RO system provides two significant barriers, in the form of 

two dense, non-porous membranes, which allows for the system to treat highly impaired water 

with high rejection of solutes. The FO membrane will act to reject most contaminates in the feed 

water, including scale forming minerals, most organic compounds, and microorganisms. 

Employing a SWRO membrane for the RO stage will ensure high NaCl rejection (exceeding 

99.7%) [69, 91]. The estimated water recovery for an FO-RO system is in excess of 96% [69]. 

FO membrane elements are not yet optimized and therefore require a larger operational 

footprint to achieve a similar water recovery to an RO system of equivalent production capacity. 

FO-RO systems may be deployed in highly portable, trailer mounted membrane skids, and are 

highly modular. An FO-RO system requires a stable source of electrical energy to operate. 

System cleaning is highly dependant on feed water quality; however, the FO membrane in highly 

resistant to membrane fouling and scaling. Mechanical cleaning of FO membrane modules has 
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been shown to be a highly efficient method for restoring membrane performance without the 

need for chemicals [72]. However, chemical cleaning and the addition of scale inhibitors may be 

required for both the FO and RO subsystems depending on feed water quality. 

The service life of an FO-RO system is currently unknown, however RO membrane 

elements will likely require replacement within 3 to 7 years of operation [36]. Industrial scale 

FO-RO systems would be highly automated systems, and would require relatively little 

supervisory oversight. The FO subsystem is capable of treating highly variable feed water 

qualities and protects the RO membrane modules from harmful membrane foulants. The system 

would require few major maintenance periods; however, the system would need to undergo brief, 

routine backwashing and mechanical cleanings several times each day. Optimization is 

underway. The FO component of an FO-RO system provides excellent pretreatment capabilities, 

while the concentrated brine generated from the RO system is continuously recycled in the 

system. The most significant waste stream that will require either further treatment or disposal is 

the concentrated feed stream. Additionally, the FO draw solution may require infrequent disposal 

and addition of a new draw solution as sparingly soluble solutes and other membrane foulants 

slowly accumulate in the draw solution reconcentration loop [92]. A summary of the technical 

assessment for an FO-RO system is listed in Table 21. 

Table 21. Summary of technical assessment of hybrid FO-RO system. 

Criteria Description/Rationale 

Industrial status One pilot-scale test on secondary effluent from a municipal wastewater 

treatment plant. No previous utilization for CBM produced water 

treatment. 

Feed water quality bins The estimated TDS application range is between 500 mg/L and 35,000 

mg/L. High removals of monovalent and divalent ions, metals, and 

organics is expected. 

Product water quality Treatment process permeate quality is dependent on feed water salinity 

and operating conditions. Pilot-scale studies report greater than 99% 

rejection of TDS in RO permeate. 

Production efficiency 

(recovery) 

Product water recovery is estimated to exceed 96%. 

Infrastructure considerations This treatment process will require a larger footprint that conventional 

RO systems. Chemical storage will be required, in addition to a FO 

membrane bank. 

System mobility is reduced compared to conventional RO systems. 

Energy consumption Energy requirements are estimated between 5.68 to 11.36 kWh/kgal 

(0.24 to 0.48 kWh/bbl) [91]. 

Chemicals Chemical cleaning rates depend on feed water quality. Cleaning will 

typically occur after certain design specifications are exceeded, and 

may require the use of NaOH, Na4EDTA, or HCl. 

Life cycle No data is currently available for hybrid system; however, RO 

elements will likely require replacement between 3 and 7 years of 

operation. 
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Table 21. Summary of technical assessment of hybrid FO-RO system. 

Criteria Description/Rationale 

O&M considerations Monitoring and control required for flow rates, chemical dosing, and 

RO element pressure. 

System may require substantial oversight to ensure proper operation of 

integrated system. 

Level of flexibility: Highly flexible to alterations in feed water quality. 

Level of robustness: TFC membranes have high pH tolerance, but 

cannot be exposed to feed temperatures in excess of 113 °F (45 °C). 

FO membranes are typically composed of cellulose acetate and are 

more resistant to oxidants that TFC membranes, but less resistant to 

low or high pH operation. 

Level of reliability: RO systems operate semi-continuously with 

automated, short duration chemical rinses or osmotic backwashing 

cycles (for RO). FO systems may operate semi-continuously with short 

duration, high flow rate mechanical cleanings. 

Types of energy required: electrical. 

Overall costs Capital costs for FO-RO systems are currently unknown. 

Pre-and post treatment Process may require pretreatment options including antiscalant and 

acid addition. 

Product water may require pH stabilization or remineralization. This 

may be achieved by lime bed contacting or by blending small amounts 

of filtered and sterilized feedwater with permeate. 

The concentrated feed stream may require additional post treatment or 

disposal consideration. 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. Relatively high recovery 

rates exceeding 96% generate very minor amounts of concentrated 

brine. 

Applicability for produced 

water treatment 

Moderate to good – FO provides an excellent pretreatment option for 

the RO stage; however, FO membrane modules are not yet optimized 

for use in CBM produced water treatment. 

Note: 1 barrel = 42 US gallons 

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Dual NF 

In this approach the concentrate from a primary NF process is employed as the feed 

solution for an additional NF stage. The second NF stage produces additional permeate that 

enhances the recovery of the overall process. This technology is currently under consideration 

for municipal brackish water desalination projects, including an ongoing study at the Irvine 

Ranch Water District (IRWD) in California. Recoveries of 92% are achieved in the primary NF 

system of the IRWD dual NF system, however the challenge water contains relatively low levels 

of sparingly soluble salts [36]. Currently, the concentrate from the full-scale primary NF system 

is being sent to a pilot skid comprised of a secondary NF system. Overall recoveries of about 

98% have been obtained [93]. More challenging feed water, such as water with high hardness, 

would likely force the dual NF system to operate with an intermediate chemical precipitation 

stage, such as dual RO with chemical precipitation. This intermediate chemical precipitation 

stage would allow for the removal of sparingly soluble salts that are near their saturation limit, 

and would otherwise lead to severe scaling of the secondary NF. 

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Thermal Technologies 

In distillation processes, energy is used to heat feed water that evaporates and then 

condenses to become purified water. Distillation technologies were traditionally used for large 

seawater desalination plants until the 1980s. In the past few decades the development of 

membrane separation processes such as RO and NF made them the technology of choice for 

most seawater and brackish water desalination; this is largely due to the higher energy 

requirements of conventional thermal desalination processes. Thermal separation processes are 

still employed in places where waste heat is readily available from power plants or other 

industries; this is particularly relevant in the Persian Gulf, where the cost of energy is relatively 

lower. 

Thermal separation technologies that are used for desalination include multi stage flash 

(MSF) distillation, multiple effect distillation (MED), and vapor compression distillation (VCD) 

[94]. In MSF, the feed water is heated, the pressure is lowered, and the water "flashes" into 

steam. This process constitutes one stage of a number of stages in series, each operating a lower 

temperature and pressure [95]. In MED, the feed water passes through a number of evaporators 

in series. Vapor from one series is subsequently used to evaporate water in the next series. The 

VCD process involves evaporation of feed water, compression of the vapor, and then recovering 

the heat of condensation to evaporate more feed water. Some distillation plants are hybrids of 

more than one desalination technology, such as MED-VCD [96]. The waste product from these 

processes is a solution with high salt concentration. By using hybrid thermal technologies, zero 

liquid discharge can be achieved through brine concentrator and crystallizer. 

Membrane systems typically have advantages over thermal processes. These include 

lower energy consumption, lower capital cost, and smaller physical footprint. However, feed 

water to membrane systems requires extensive pretreatment, and the processes are not applicable 

to very high salinity water (e.g., above seawater level of approximately 47,000 mg/L TDS). 

Recent innovations in materials, chemical additives for scale and corrosion control, and process 

engineering make thermal processes more attractive and competitive in certain applications, 

particularly for achieving zero liquid discharge and treating highly contaminated water. Besides 

distillation technologies, new thermal separation technologies such as freeze-thaw and 

dewvaporation have been developed for desalination of water. 

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Multi stage flash 

The multi stage flash (MSF) distillation process is based on the principle of flash 

evaporation in which water is evaporated by reducing the pressure as opposed to raising the 

temperature with additional heat/energy. In MSF the heated feed water flows into a stage with 

lower pressure and immediately boils or flash into steam [94]. The high efficiency of the MSF 

process is achieved by preheating new feed water through capturing of the heat of condensation 

in each flash chamber or stage. 

A simplified schematic of an MSF seawater desalination plant is shown in Figure 18. The 

incoming seawater passes through the heating stage(s) and is preheated in the heat 

recovery/condenser sections of each subsequent stage. After passing through the last heat 

recovery section, and before entering the first stage, the feed water is further heated to the boiling 

temperature of the first stage in the brine heater using externally supplied energy or steam. This 

raises the feed water to its highest temperature, after which it is passed through the stages where 

flashing takes place. The vapor pressure in each of these stages is controlled so that the heated 

brine enters each chamber at the superheated conditions associated with the temperature and 

pressure of each stage (each lower than the preceding stage) to induce instantaneous 

boiling/evaporation [97]. 

The fresh water is produced by condensation of the steam, which is collected at each 

stage. The desalinated water produced by the MSF process contains typically 2–10 mg/L TDS, 

and requires remineralization through post-treatment process [98][99]. 

The range of recoveries for conventional MSF desalting process is limited to 

approximately 10-20% for seawater [94]. 

Figure 18. Simplified schematic of MSF seawater desalination plant (Source: [97]). 

According to the Global Water Intelligence (GWI) report, MSF had a market share of 

more than 60% of the worldwide desalination capacity in 2003 and decreased to 34% by the end 

of 2005 due to the competition of membrane technologies [38]. MSF can be applied to a wide 
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range of feed water quality bins including produced water. MSF often requires centralized design 

and construction of large-scale plants. 

Formation of scale on heat transfer surfaces is a major operating problem in thermal 

desalination processes. It impedes the rate of heat transfer rates on condensing and heat transfer 

surfaces, and will consequently reduce the distiller performance. The majority of MSF plants are 

currently using scale inhibitors such as phosphonates or polycarboxylic and polymaleic acids in 

conjunction with mechanical sponge ball cleaning to control alkaline scale formation [96]. Acid 

cleaning may be required if scale formation is not controlled by using the scale inhibitors and 

mechanical cleaning. 

Well designed and operated, some MSF distillers have been in service for more than 20 

years, and are expected to exceed 30 years [96]. This increases the cost effectiveness of process. 

A summary of the technical assessment of MSF is listed in Table 22. 

Table 22. Summary of technical assessment of MSF.

Criteria Description/Rationale 

Industrial status Mature and robust technology for seawater and brackish water 

desalination. Can be employed for produced water treatment. 

Feed water quality bins Usually applicable to a high TDS range to 40,000 mg/L, and all types 

of water chemistry makeup. 

Product water quality Product water quality for MSF plants is typically very high (TDS 2-10 

mg/L), with little variation due to feed or concentrate salt content. 

Production efficiency 

(recovery) 

Product water recovery is between 10% and 20% [94]. 

Infrastructure considerations The infrastructure considerations or constraints are large physical plant 

size. 

The technology relies on the availability of low-pressure steam, either 

by dedicated generation or by cogeneration arrangements with adjacent 

power plants. 

The MSF plants have low mobility. 

Energy consumption In addition to the 11 to 21 kWh/kgal (0.45-0.9 kWh/bbl) of energy 

required for electricity, the thermal energy needs for a MSF distillation 

plant is estimated at 0.8 million Btu/kgal (about 80 kWh/kgal or 3.35 

kWh/bbl) [95]. Consequently, the total energy needs for MSF are 

between 70 and 112 kWh/kgal (or 3.35-4.70 kWh/bbl) [95] [100]. 

Chemicals Scale inhibitor and acid may be required for process control to prevent 

scaling. Corrosion control is achieved via pH control. Annual cleaning 

is typically conducted using acid, EDTA, or other antiscaling 

chemicals. 

Life cycle Typically 20 years, although most plants built in the 1970’s and 1980’s 

are still in operation with expected life of over 30 years. 
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Table 22. Summary of technical assessment of MSF.

Criteria Description/Rationale 

O&M considerations Levels of monitoring and control required for feed pH, flow rates as 

well as steam and vessel pressures. 

High level of skilled labor required, however lower than equivalent 

membrane plants. 

Level of flexibility: easy to adapt to highly varying water quality; not 

flexible for varying water flow. 

Level of robustness: high ability of the equipment to withstand harsh 

conditions. 

Level of reliable: typical plants operate continuously, with shutdown 

only for planned maintenance once per year (6-8 weeks) [97]. 

Types of energy required: thermal and electricity. 

Overall costs Capital costs vary from $6–8.6/gpd (or $250-360 per bpd), depending 

on various factors including size, materials of construction and site 

location [98]. As a non-modular form of construction, the economy of 

scale can reduce the cost for larger plants, assuming ready site access 

for marine transportation. Operating costs are approximately $3/kgal 

(or $0.12/bbl), and total unit costs are $4.4/kgal (or $0.19/bbl) [98]. 

Significant reductions in energy costs can be realized from 

cogeneration arrangements where cheap, low-pressure steam is 

available. 

Pre-and post treatment One of the advantages of MSF compared to membrane technologies is 

that the general operation requires less rigorous pretreatment and feed 

conditioning. Feed water requires screens and rough filtration to 

remove large suspended solids. Since the elevated process 

temperatures will automatically sterilize the water, there is no need to 

add biocides once the water enters the MSF units. 

Product water needs stabilization because of the low TDS level. This 

may be achieved by lime bed contacting or by blending small amounts 

of filtered and sterilized feedwater with the distillate. 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. Due to the typically low 

recovery rates of 25 to 30%, large amounts of concentrate are 

generated. 

Applicability in produced water 

treatment 

Good for high TDS produced water treatment. MSF often requires 

centralized design and construction of large-scale plants. 

Note: 1 barrel = 42 US gallons 

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Multi effect distillation 

The basic principle of a multi effect distillation (MED) system is to apply sufficient 

energy to bring the feed water to its boiling temperature and then to deliver the additional energy 

needed for the heat of vaporization to transform a portion of the saline water to steam. The final 

step is to condense the process steam as pure water. 

A “single stage” operation is very energy intensive. Multiple vessels can be used to make 

the process more efficient by operating the vessels (or effects) at successively reduced pressures 

to promote boiling at lower temperatures, and thus achieving multiple boiling and evaporation 

cycles, without the addition of more heat. Typically, 8 to 16 effects may be used in MED to 

minimize the energy consumption. A schematic of a conventional MED system using steam as a 

heat source, with four effects is illustrated in Figure 19. The feed water is distributed on the 

outside of the evaporator tubes in a thin film to promote rapid boiling and evaporation. Steam is 

condensed on the colder inside surface. The vapor produced in each effect is used to heat the 

feed water in the next effect. The following are the energy consuming components of an MED 

process: 

 Steam of sufficient pressure to drive evaporation in the first stage. 

 Energy for vacuum systems to reduce the boiling pressure in the downstream effects 

(if operated at low temperatures). 

 Energy to pump the feed through the heat exchangers to the evaporator(s), to recirculate the brine within each evaporator stage and to pump the condensate and 

brine through the heat recovery for exiting the system. 

 Cooling water to condense the steam from the final stage. 

Figure 19. Schematic of a conventional MED system using steam as a heat source 

(Source: [101]). 

Energy efficiencies may be gained through combination of the evaporator systems with 

available low-pressure or waste steam/heat sources and by the addition of efficiency 

enhancement devices to a conventional MED system. 

Although the MED is an older technology than the MSF, it has not been extensively 

utilized for water production as MSF because of scaling problems associated with old designs. 

Recently, considerable improvements in MED systems have been introduced to reduce the 

undesirable characteristics (e.g., low heat transfer rate and high rates of scale formation) of the 
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old MED submerged tube evaporators. Falling film evaporators such as vertical tube evaporator 

(VTE) and the horizontal tube evaporator (HTE) of new MED plants have a number of distinct 

advantages [96]. They provide higher overall heat transfer coefficients and low specific heat 

transfer surface area compared to MSF desalination systems. They do not employ recycling; thus 

they are based on the once through principle and have low requirements for pumping energy. 

MED process has recently made substantial progress for small thermal desalination plants. 

According to the GWI report, MED had a market share of 6.9% of the worldwide desalination 

capacity by 2005 [38]. The largest MED unit was commissioned in Layyah desalination plant in 

Sharjah (UAE) in 2001. It consists of two MED units each with a capacity of 6 MGD (143,000 

bbl per day) [96]. 

Like MSF, MED can be applied to a wide range of feedwater quality, including produced 

water. MED also offers the possibility of reducing plant size and footprint. The range of 

recoveries for conventional MED desalting process is limited to 20-35% for seawater, and 67% 

for stacked vertical tube design [94]. A summary of the technical assessment of MSF is listed in 

Table 23. 

Table 23. Summary of technical assessment of MED. 

Criteria Description/Rationale 

Industrial status Mature and robust technology for seawater and brackish water desalination. 

Can be employed for produced water treatment. 

Feed water quality bins Applicable to a wide TDS range, and all types of water chemistry makeup. 

Product water quality Product water quality for MED plants is typically very high, with little 

variation due to feed or concentrate salt content. 

Production efficiency 

(recovery) 

Product water recovery is between 20% and 35% for horizontal and vertical 

tube design, and 67% for stacked vertical tube design [94]. 

Infrastructure 

considerations 

Infrastructure considerations are similar to MSF, and MED units are of 

smaller capacity. 

Energy consumption The power consumption of an MED plant is significantly lower than that of 

an MSF plant, and the performance ratio of the MED plant is higher than 

MSF plant. The electrical consumption is 11 kWh/kgal (0.48 kWh/bbl) [98]. 

The power energy consumption of MED is in the range of 31-45 kWh/kgal 

(1.3-1.9 kWh/bbl) [100]. 

Chemicals Scale inhibitor and acid may be required for process control to prevent 

scaling. Corrosion control is achieved via pH control. Annual cleaning is 

typically conducted using acid, EDTA, or other antiscaling chemicals. 

Life cycle Typically 20 years. Operational experience of the MED plants operating 

since 1970’s and 1980’s in Middle East revealed that the specified 

performance has been consistently satisfied and no major problems have 

been experienced [96]. 
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Table 23. Summary of technical assessment of MED. 

Criteria Description/Rationale 

O&M considerations Levels of monitoring and control required for feed pH, flow rates as well as 

steam and vessel pressures. 

High level of skilled labor required, however lower than equivalent 

membrane plants. 

Level of flexibility: easy to adapt to highly varying water quality; not 

flexible for varying water flow. 

Level of robustness: high ability of the equipment to withstand harsh 

conditions. 

Level of reliable: typical plants operate continuously, with shutdown only 

for planned maintenance once per year. 

Types of energy required: thermal and electricity. 

Overall costs Because energy consumption of MED is lower than MSF, the overall cost is 

less than MSF. 

Capital costs vary from $6–8/gpd (or $250-330 per bpd), depending on 

various factors including size, materials of construction and site location 

[98]. As a non-modular form of construction, the economy of scale can 

reduce the cost for larger plants, assuming ready site access for marine 

transportation. Operating costs are approximately $2.6/kgal (or $0.11/bbl), 

and total unit costs are $3.8/kgal (or $0.16/bbl) [98]. 

Pre-and post treatment Similar to MSF, MED requires less rigorous pretreatment and feed 

conditioning as compared to membrane treatment. Product water needs 

stabilization because of the low TDS level. This may be achieved by lime 

bed contacting or by blending small amounts of filtered and sterilized 

feedwater with the distillate. 

Concentrate management 

or waste disposal 

No special concentrate treatment is required. Due to the typically low 

recovery rates of 20-35%, large amounts of concentrate (65-80%) are 

generated. 

Applicability in produced 

water treatment 

Good for high TDS produced water treatment. MED often requires 

centralized design and construction of larger plants. 

Note: 1 barrel = 42 US gallons 

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Vapor Compression Distillation 

In vapor compression distillation (VCD) systems, mechanical (mechanical vapor 

compression or MVC) or thermal (thermo vapor compression or TVC) compression of the vapor 

provides the heat for evaporation. The process compresses the vapor generated within the unit 

itself. The mechanical compressor is usually electrically or diesel driven. Thermal compression 

uses high-pressure steam. Compression raises the pressure and temperature of the vapor so that it 

can be returned to the evaporator and used as a heat source. 

A schematic of a VC system using steam as a heat source, with four effects stages is 

illustrated in Figure 20. Water vapor is drawn from the evaporation chamber by a compressor 

and except for the first stage the vapor is condensed on the outsides of tubes in the same 

chambers. The heat of condensation is used to evaporate a film of saline water applied to the 

insides of the tubes within the evaporation chambers. The low temperature VCD is a simple, 

reliable, and efficient process. Having a high capacity compressor allows operation at 

temperatures below 70°C, which reduces the potential for scale formation and corrosion [99]. 

The VCD process is generally used for small-scale desalination units; ranging from 0.026 

to 0.79 MGD (1,100 - 18,000 bbl per day). The power consumption of larger units is 

approximately 30 kWh/kgal of product water (1.3 kWh/bbl) [99]. The VCD process is well 

established and is used for seawater desalination as well as treating produced water and RO 

concentrate (i.e., brine concentrator application) in a near-zero liquid discharge (ZLD) 

application. VCD units are often used for resorts, industries, and drilling sites where fresh water 

is not readily available. 

 Vapor compression allows higher water recovery compared to conventional MSF and 

MED; the range of recoveries for conventional VCD is 40% for seawater [94]. To achieve ZLD, 

VCD can work as a crystallizer and the energy demand for concentrate evaporation and 

crystallization is 100-250 kWh/kgal (4.2 to 10.5 kWh/bbl) [102]. A summary of the technical 

assessment of VC is listed in Table 24. 

Figure 20. Simplified schematic of a VCD unit (Source: [94]). 
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Table 24. Summary of technical assessment of VCD. 

Criteria Description/Rationale 

Industrial status Mature and robust technology for seawater and brackish water desalination. 

Various enhanced VC technologies have been employed for produced water 

treatment. 

Feed water quality bins Applicable to high TDS water > 40,000 mg/L, and all types of water 

chemistry makeup. 

Product water quality Product water quality for VC plants is typically very high, with little 

variation due to feed or concentrate salt content. 

Production efficiency 

(recovery) 

Product water recovery is approximately 40% for desalination; for ZLD, 

VC works as a crystallizer and achieve high recovery. 

Infrastructure 

considerations 

Infrastructure considerations are similar to MSF and MED units, but VCD 

units are of small scale. 

Energy consumption The power consumption of a VCD plant is significantly lower than that of 

MSF and MED plants. For desalination, the power energy consumption of 

large VC plant is approximately 30 kWh/kgal (1.3 kWh/bbl) of product 

water [99]. The electricity consumption is 26.5 kWh/kgal (1.1 kWh/bbl) for 

MVC [98]. To achieve zero-liquid discharge, the energy demand for 

concentrate evaporation and crystallization is about 100 to 250 kWh/kgal 

(4.2 to 10.5 kWh/bbl) [102]. 

Chemicals Scale inhibitor and acid may be required for process control to prevent 

scaling. Corrosion control is achieved via pH control. Annual cleaning is 

typically conducted using acid, EDTA, or other antiscaling chemicals. 

Life cycle Typically 20 years, although longer life may be expected with the selection 

of better materials of construction, that is, alloys with high corrosion 

resistance. 

O&M considerations Levels of monitoring and control required for feed pH, flow rates as well as 

steam and vessel pressures. 

High level of skilled labor required. VCD, especially MVC is a more 

complex system and adds to the O&M skill level required. 

Level of flexibility: easy to adapt to highly varying water quality; not 

flexible for varying water flow. 

Level of robustness: high ability of the equipment to withstand harsh 

conditions. 

Level of reliable: typical plants operate continuously, with shutdown only 

for planned maintenance once per year. 

Types of energy required: thermal and electricity. 

Overall costs The capital costs depend on various factors including size, materials of 

construction and site location. The operating costs depend on the purpose of 

plant; the costs to achieve ZLD are significantly higher than desalination 

because of energy costs. Significant reductions in energy costs can be 

realized from cogeneration arrangements where low pressure steam is 

available. 

Capital costs of MVC for seawater desalination vary from $3.3–6/gpd (or 

$140-250 per bpd), depending on various factors including size, materials 

of construction and site location [98]. Operating costs are approximately 

$1.8/kgal (or $0.075/bbl), and total unit costs are $1.9/kgal (or $0.08/bbl) 

for seawater desalination [98]. 
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Table 24. Summary of technical assessment of VCD. 

Criteria Description/Rationale 

Pre-and post treatment VC requires less rigorous pretreatment and feed conditioning as compared 

to membrane treatment. Product water needs stabilization because of the 

low TDS level. This may be achieved by lime bed contacting or by blending 

small amounts of filtered and sterilized feedwater with the distillate. 

Concentrate management 

or waste disposal 

No special concentrate treatment is required. For ZLD, generated mixed 

solids need waste disposal. 

Applicability in produced 

water treatment 

Excellent for high TDS produced water treatment and ZLD. 

Note: 1 barrel = 42 US gallons 

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Multi Effect Distillation – Vapor Compression Hybrid 

Both multiple-effect distillation (MED) and vapor compression evaporation (VCD) are 

state of the art technologies that have been employed for many years in desalination of seawater 

and brackish waters. More recently, hybrid MED-VCD has been employed to treat produced 

water (see more detailed discussion in commercial thermal technology processes). The 

combination of the two techniques to enhance the desalination process is frequently mentioned 

as a means of enhancing thermal desalination by reducing both capital and operating costs. This 

technology is favorable for replacing some of the older MSF plants. There is not much 

innovation in the design of such hybrids, but there are some complexities associated with the 

integration of the two processes. The advantages gained from combining the processes include: 

 Increased production 

 Expansion of capacity of existing MED units 

 Enhanced energy efficiency 

For desalination, power consumption of MED-TVC plants is approximately 7.57 

kWh/kgal (0.32 kWh/bbl) and there are no requirements to recirculate large quantities of brine 

[96]. The combination of high performance ratio and low power consumption results in lower 

overall energy costs. 

In the 1982, six MED-TVC distillers were operated in different remote sites of Abu 

Dhabi (UAE); each had a rated production capacity of 1.2 MGD [96]. Veolia Water Systems 

(France) installed an 11.1 MGD MED-VC system in Layyah (Sharjah, U.A.E.), which is claimed 

to have an energy efficiency of 50% over conventional systems. A barge mounted MED-MVC 

hybrid was built in Germany and shipped to Saudi Arabia. The advantage of such a system 

design and delivery method is that it minimizes local construction costs and shortens the interval 

between purchase and startup. A summary of the technical assessment of MED-VCD is listed in 

Table 25. 

Table 25. Summary of technical assessment of MED-VCD. 

Criteria Description/Rationale 

Industrial status Mature and robust technology for seawater and brackish water desalination. Has 

been employed for produced water treatment. 

Feed water quality 

bins 

Applicable to high TDS range, and all types of water chemistry makeup. 

Product water quality Product water quality for MED-VCD plants is typically very high. 

Production efficiency 

(recovery) 

Product water recovery is between 30% and 45% for seawater desalination. GE 

brine concentrator and crystallizer can increase water recovery to 75-85% [103]. 

Infrastructure 

considerations 

The infrastructure considerations or constraints are similar to that of MSF. 

Sufficient land must be available to accommodate the large plant footprint. The 

availability of low-pressure steam, either by dedicated generation or by 

cogeneration arrangements with adjacent power plants is essential. If using 

MVC, the system’s high the electrical demand must be considered. 

Energy consumption For desalination, power consumption of MED-TVC plants is only around 7.57 

kWh/kgal (0.32 kWh/bbl) [96]. To achieve zero-liquid discharge, the energy 

demand for concentrate evaporation and crystallization is about 100 to 250 

kWh/kgal (4.2 to 10.5 kWh/bbl) [102]. 
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Table 25. Summary of technical assessment of MED-VCD. 

Criteria Description/Rationale 

Chemicals Scale inhibitor and acid may be required for process control to prevent scaling. 

Corrosion control is achieved via pH control. Annual cleaning is typically 

conducted using acid, EDTA, or other antiscaling chemicals. 

Life cycle Typically 20 years, although longer life may be expected with the selection of 

better materials of construction, that is, alloys with high corrosion resistance. 

O&M considerations Levels of monitoring and control required for feed pH, flow rates as well as 

steam and vessel pressures. 

High level of skilled labor required. VCD, especially MVC is a more complex 

system and adds to the O&M skill level required. Hybrid designs of the two 

different technologies further add to the O&M complexity compared to the 

individual processes. 

Level of flexibility: easy to adapt to highly varying water quality; not flexible for 

varying water flow. 

Level of robustness: high ability of the equipment to withstand harsh conditions. 

Level of reliable: typical plants operate continuously, with shutdown only for 

planned maintenance once per year. 

Types of energy required – thermal and electricity. 

Overall costs Capital cost of MED-TVC is approximately $6/gpd ($250 per bbl per day) [98]. 

The costs may vary depending on various factors including size, materials of 

construction and site location. Operating costs are dependent upon energy 

consumption. Significant reductions in energy costs can be realized from 

cogeneration arrangements where low pressure steam is available. 

Pre-and post 

treatment 

MED-VC requires less rigorous pretreatment and feed conditioning as compared 

to membrane treatment. Product water needs stabilization because of the low 

TDS level. This may be achieved by lime bed contacting or by blending small 

amounts of filtered and sterilized feedwater with the distillate. 

Concentrate 

management or waste 

disposal 

No special concentrate treatment is required. For ZLD, generated mixed solids 

need waste disposal. 

Applicability in 

produced water 

treatment 

Excellent for high TDS produced water treatment and ZLD. Maybe economical 

to large flow rate and not applicable to point source of produced water wells. 

Note: 1 barrel = 42 US gallons 

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Freeze/Thaw Evaporation (FTE®) 

The freeze/thaw evaporation is a water treatment process that combines freezing and 

thawing cycle with conventional evaporation technology [104]. A schematic diagram of FTE® is 

shown in Figure 21. When the ambient air temperature is below 32 °F (0 °C), the saline water 

(feed water) is sprayed or dripped onto a freezing pad to create an ice pile. Relatively pure ice 

crystals form and an unfrozen solution (brine) containing elevated concentrations of the 

dissolved constituents drains from the ice. The runoff can be diverted to a brine storage facility 

or back to the feed water storage facility for recycling. When the temperatures rise, the ice melts 

and the runoff from the freezing pad is highly purified water that can be diverted to a treated 

water storage facility for beneficial uses or surface discharge. 

During warm months, the FTE system is operated as a conventional evaporation facility. 

During months with subfreezing (<32 °F) temperatures, a large ice pile is created by spraying the 

water to be treated in a shallow pit, and the natural freeze–thaw process takes over. FTE® allows 

water treatment and disposal on a continuous basis. 

Figure 21. Schematic of Freeze/Thaw Evaporation (FTE®) (Source: [104]). 

FTE® processes were developed by the Energy & Environment Research Center (EERC) 

and B.C. Technologies, Ltd. (BCT), in 1992 [105]. Field-scale FTE testing of CBM produced 

water treatment started in 1995. Between 1995 and 2001, three commercial-scale FTE® plants 

were deployed to simultaneously remove salts, organics, and heavy metals from wastewaters 

generated in natural gas production fields in New Mexico and Wyoming [105]. Industrial 

partners in these operations included Amoco Production Company, McMurry Oil Company, 

Crystal Solutions, and Gas Research Institute. Results from these field tests confirm both the 

process economic viability and its potential to produce usable, quality treated water from oil and 

natural gas produced water. As of 2003, two FTE plants continued to operate commercially in 

Wyoming: one in the Jonah gas field south of Pinedale and the other in the Red Desert near 

Wamsutter (Figure 22). The treatment capacity of those plants is more than 40,000 gallons a day 

(950 bbl/day) [105]. 
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Figure 22. Photo of FTE® Field Performance in Wamsutter, Wyoming (Source: [104]). 

The FTE® facility in the Great Divide Basin of WY was originally constructed and 

operated by Crystal Solutions (CS) (1999-2003) and is now owned by Samson Resources 

Company and operated by CS. The initial nominal plant capacity (1999-2002) was 500 bbl/day, 

and current plant capacity (2003 to present) is 1,000 bbl/day. Approximately 1.8 million bbl of 

produced water have been treated at the facility to date [104]. 

The FTE® process has been proven in commercial operations to be capable of treating a 

broad variety of wastewater, and of removing over 90% of produced water constituents [104], 

including total suspended solids (TSS), total dissolve solids (TDS), total recoverable petroleum 

hydrocarbons (TRPH), volatile organic compounds (VOC), semi-volatile organic compounds, 

and heavy metals. However, the FTE® process is not capable of treating wastewater having more 

than 5% methanol. The FTE® operation performance during wintertime is shown in Table 26. A 

technical assessment of FTE® process is summarized in Table 27. 

Table 26. FTE® operation in the Great Divide Basin of Wyoming in winter 2001-2002. 

(Source: [104]) 

Volume (bbl) TDS (mg/L) TPH (mg/L) 

Feed 102,440 9,790 39.1 

Brine 38,119 44,900 63.2 

Treated Water 52,356 1,000 3.1 

Sub. + Evap. 11,965 

Table 27. Summary of technical assessment of FTE®. 

Criteria Description/Rationale 

Industrial status Mature and robust technology for produced water treatment and disposal. 

Feed water quality bins As an evaporation process, the applicable feedwater TDS could be >40,000 

mg/L. Produced water with high methanol concentration cannot be treated. 

Product water quality Product water quality is moderate with TDS in the range of 1000 mg/L [104]. 

The FTE® process can remove over 90% of the following types of produced 

water constituents: TSS, TDS, TRPH, volatile and semi-volatile organic 

compounds, heavy metals. 

Production efficiency 

(recovery) 

Product water recovery is approximately 50% during wintertime. No water can 

be recovered during other seasons as the process works as a conventional 

evaporation pond. 
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Table 27. Summary of technical assessment of FTE®. 

Criteria Description/Rationale 

Infrastructure 

considerations 

The FTE® process does not require infrastructure or supplies that limit its use. 

However, the FTE® process has several inherent features that severely limit it 

application ([104]): 

 The FTE® process requires a climate with a substantial number of days 

with temperatures below freezing. 

 The FTE® process requires a significant amount of land – 35 acres for a 

1,000 bbl facility. 

 The FTE® process requires proper hydro-geologic setting including 

favorable soil conditions, locations of legal waters and characteristics of 

near surface aquifers. 

Energy consumption Not available. 

Chemicals No chemicals 

Life cycle Expected 20 years. 

O&M considerations Low level of monitoring and control. 

Low level of skilled labor required. 

High level of flexibility: easy to adapt to highly varying water quality and 

quantity. 

High level of robustness. 

High level of reliability. 

Types of energy required – electricity. 

Overall costs The FTE® process economics are strongly application and location specific. In 

most of Wyoming, a 42,000 gal/day (1,000 bbl/day) facility will require total 

installed capital costs of $1.75 to 2.0 million for a turnkey operation and 

annual operating expenses range from $0.031 to 0.042/kgal ($0.75 to 

$1.00/bbl). Thus, using the FTE® process in most of Wyoming, produced water 

total amortized produced water treatment costs range from $0.062 to 

0.079/kgal ($1.50/bbl to $1.87/bbl): with amortized capital costs range from 

$0.75/bbl to $0.87/bbl assuming 15% rate of return on capital and 20 year plant 

life [104]. 

Pre-and post treatment The FTE process requires minimal pre-treatment of produced water. For 

example the pretreatment at the Samson Resources facility in the Great Divide 

Basin of WY is limited to removal of product oil and tank bottoms using two 

400 bbl gun-barrel oil-water separators. In CBM applications, pretreatment 

would not be necessary if product oil is not present in the water. 

Post-treatment will depend on the product water quality and beneficial use 

applications or discharge standards. 

Concentrate 

management or waste 

disposal 

The FTE® process generates waste streams: oil from the oil water separators (if 

present), and concentrated brine. Currently, the brine is allowed to passively 

evaporate in evaporation ponds. Long-term plans are to allow the concentrate 

to evaporate to a solid at the end of the facility operation and dispose of the 

material in a permitted landfill. 

Applicability in 

produced water 

treatment 

Excellent for ZLD of produced water, may be limited by land availability and 

climate conditions. 

Note: 1 barrel = 42 US gallons 

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Dewvaporation – AltelaRainSM Process 

Dewvaporation is a process that involves humidification-dehumidification desalination. It 

reduces the energy costs by using counter-current heat exchange technology. Feedwater is 

evaporated by heated air, which condenses as fresh water on the opposite side of a heat transfer 

wall. The energy needed for evaporation is partially supplied by the energy released during 

condensation. Heat sources can be combustible fuel, solar, or low-grade heat from various 

resources. The tower unit is built of thin plastic films to avoid corrosion and to minimize 

equipment costs. Towers are relatively inexpensive because they operate at atmospheric pressure. 

Altela, Inc. has designed, manufactured, and tested several AltelaRainSM prototype 

systems based on the dewvaporation process. A schematic of the AltelaRainSM process is shown 

in Figure 23. Three full-scale AltelaRainSM ARS-4000 systems have been deployed at natural 

gas wells in the San Juan Basin near Farmington, NM [106]. The ARS-4000 system can process 

approximately 4,000 gallons per day (100 bbl/day) of produced water with salt concentrations in 

excess of 60,000 mg/LTDS. 

Figure 23. Schematic of AltelaRainTM process (Source: [107]). 

AltelaRainSM System can reduce effluent disposal volumes by as much as 90%. Because 

the treated water stream is distilled water, the AltelaRainSM produces very high quality water. In 

one test the TDS concentration of produced water was reduced from 41,700 mg/L to 106 mg/L 

and chloride concentration was reduced from 25,300 mg/L to 59 mg/L [108]. Similarly, benzene 

concentration was reduced from 450 g/L to non-detectable following AltelaRainSM treatment 

[108]. 

The AltelaRainSM technology requires no special infrastructure, supplies, or consumables 

for its unattended operation. It requires only regular 110V electricity (from either a generator or 

solar panels), making it a water treatment alternative at remote wells where no high power grid is 

available. Dewvaporation operates primarily from low-grade heat source that generates steam at 

atmospheric pressure. It can come from a variety of sources, such as industrial waste heat, or 

well-site gas. At locations where either waste heat or waste gas is not readily available, steam 

can be generated using a small natural gas-fired boiler. Altela currently operates three systems in 
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such remote locations that both the electricity and heating needs are satisfied by using natural gas 

from the well that produces the water [106]. 

Like other evaporative processes, the energy consumption of the dewvaporation system is 

high. In a report published by the U.S. Bureau of Reclamation [109], the authors provided the 

following estimate of energy consumption and cost for a dewvaporation system: 

 Electrical cost for pumps and fans: $0.05 per 1,000 gallons (0.5 kWh per 1,000 gallons 

at ¢10 cents per kWh) [109]. 

 Other energy cost: using the average multiple effect value of 3.2, the heat needed for 

1,000 gallons of distillate production would be 2.6 million BTUs (764 kWh heat). At a 

natural gas cost of ¢80 per therm, the operating cost would be $20.85 per 1,000 gallons. 

If waste heat or solar heat were available, the operating cost would reduce to the 

electrical cost of pumps and fans [109]. 

A technical assessment of the AltelaRainSM process is summarized in Table 28. 

Table 28. Summary of technical assessment of AltelaRainSM process. 

Criteria Description/Rationale 

Industrial status Full-scale application for produced water treatment. 

Feed water quality bins Applicable to TDS up to 40,000 - 60,000 mg/L, and a broad variety of water 

chemistry makeup. 

Product water quality Product water quality is very high with TDS in the range of 20-100 mg/L 

[106, 108]. The process also has high removal rate of heavy metals, organics, 

and radionuclides. 

Production efficiency 

(recovery) 

Product water recovery is approximately 90%. 

Infrastructure 

considerations 

No special infrastructure, supplies, or consumables for its unattended 

operation. 

Energy requirements include 110V electricity (from either a small generator 

or solar panels), and thermal (either from industrial waste heat, well-site flash 

gas, or using a small natural gas-fired boiler). 

Energy consumption Altela, Inc. claims that electricity requirement is low because the system 

operates at ambient pressures and low temperature [106, 108]. The AltelaRain 

system yields energy costs that are approximately only 30% of comparable 

ambient pressure distillation/evaporation processes. The ‘Multiple-effect’ 

energy savings are comparable to that achieved by pressure distillation 

methods such as MVC. 

Chemicals No chemicals. 

Life cycle No data available. 

O&M considerations Low level of monitoring and control. 

Low level of skilled labor required. 

High level of flexibility: easy to adapt to highly varying water quality and 

quantity. 

High level of robustness. 

High level of reliability. 

Types of energy required –electricity and thermal. 

Overall costs Not available. The Altela reported the cost structure associated with building, 

installing, maintaining, and servicing the system is lower than the escalating 

costs associated with traditional produced water hauling and reinjection. 
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Table 28. Summary of technical assessment of AltelaRainSM process. 

Criteria Description/Rationale 

Pre-and post treatment Require no pre-treatment. Screens (>300 micron) are required if debris 

present in produced water to protect the pumps and valves in the incoming 

lines. 

Product water needs remineralization because of the low TDS level. This may 

be achieved by lime bed contacting or by blending small amounts of filtered 

and sterilized feedwater with the distillate. 

Concentrate 

management or waste 

disposal 

The current 10% brine stream is transported off the well site and then either 

injected into a disposal well or evaporated/stored in large ponds. 

Applicability in 

produced water 

treatment 

Excellent for produced water application. Like other evaporative processes, 

high energy-consumption might be a limiting factor for its applicability if no 

waste heat or cheap energy sources are available. 

Note: 1 barrel = 42 US gallons 

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Alternative Technologies 

Ion exchange process 

In ion exchange (IX), removal of specific ions or compounds from a stream is facilitated 

by the exchange of a pre-saturated ion with the target ions on an IX resin. Contaminant cationic 

solutes such as calcium, magnesium, barium, strontium, and radium are removed by cation 

exchange resins, and anionic solutes such as fluoride, nitrate, fulvates, humates, arsenate, 

selenate, chromate, and anionic complexes of uranium may be removed by anion exchange 

resins [110]. Recent research also suggests that IX may be employed to remove boron from RO

permeate [111]. IX is a well-developed process and is commonly applied to drinking water 

treatment for hardness removal, but is increasingly being studied for the removal of 

radionuclides and nitrates [110, 112]. 

IX resins are typically composed of synthetic resins or activated alumina. These resins 

are characterized as either strong or weak and may be acidic or basic in nature. Acidic ion 

exchange resins are utilized to remove unwanted cations from solution. Examples of frequent 

chemical reactions for IX in strong and weak acid resins and in basic IX resin are shown below: 

2(R  SO3H)  Ca2  (R  SO3)2Ca  2H (strong acid resin) 

2(R COOH)  Ca2  2HCO3

  (R COO)2Ca  H2O  CO2 (weak acid resin) 

(R  NH3OH)  HCl  (R  NH3Cl)  H2O (basic resin) 

IX resins are typically manufactured to have readily reversible reactions, which allows 

for the IX resin to be regenerated once its adsorptive capacity is exhausted. The IX resin’s 

adsorptive capacity is exhausted when the target ion reaches a prescribed breakthrough 

concentration in the IX product water. To achieve high purity water quality, many conventional 

IX processes are operated with mixed beds to achieve removal of both cations and anions. 

Regeneration occurs by flooding the IX resin with a solution that is highly concentrated with the 

pre-saturated ion. During standard operation an IX bed may treat between 300 to 300,000 bed 

volumes (BV) before requiring regeneration, depending on the adsorptive capacity of the resin 

and the feed water quality [110]. Regeneration typically requires 2 to 20 BV of rinse water 

(generally less than 2% of the product water) to restore the adsorptive capacity of the IX resin 

[110]. 

IX systems are typically installed in fluidized, packed bed configurations. IX is an 

established water treatment technology that is utilized for municipal drinking water treatment, 

wastewater treatment, and CBM produced water treatment (especially in the Powder River 

Basin) [110, 113]. The operational footprint for most IX processes includes packed resin beds 

(sometimes referred to as columns) and onsite regenerant and cleaning chemical storage. The 

type of regenerant chemicals depends on the characteristics of the IX resin employed and may be 

include solution of H2SO4, HCl, NaOH, Na2CO3, or NaCl. 

Typically, IX processes operate with minimal energy demand and may require only 

electricity for pumping fluids under low hydraulic pressure. Operation and management 

considerations for IX include occasional disinfection of IX resin with NaOCl or H2O2. Careful 

management of the feed stream is also necessary to ensure that fouling agents such as suspended 
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solids, scale forming materials (e.g., CaSO4), and oxidized metal are not present in the feed 

water. Additionally, many IX resins are sensitive to free chlorine oxidation. IX processes must 

also be carefully managed to reduce osmotic shock and mechanical abrasion of IX resin, which 

will lead to physical loss of the resin [114]. 

Operating costs for standard IX processes vary greatly with feed water quality and 

loading rate. An economic feasibility analysis conducted by DowEX (Dow Chemical Company, 

Midland, MI) estimated that IX, after a conventional pretreatment (e.g., coagulation, 

flocculation, and sedimentation), could be used to treat surface water to a quality of less than 1 

μS/cm in conductivity. The costs for IX vary between $1.9-2.6/kgal ($0.08-0.11/bbl) at 220 gpm 

(5 bbl per minute) and $1.0-1.7/kgals ($0.04-0.07/bbl) at 880 gpm (21 bbl per minute). At the 

lower flow rate, operating costs account for ~70% of the total cost with regenerants, raw water, 

labor and maintenance making the most significant contributions. At 880 gpm, operating costs 

increase to ~80% [115]. 

 Waste disposal needs of IX processes include the need to neutralize and dispose of spent 

IX regenerant solution. These solutions typically represent a very low volume of wastewater, but 

may be highly saline and require additional treatment to limit disposal costs. Product water from 

IX processes may require SAR adjustment [19]. A summary of the technical assessment for 

general IX processes is shown in Table 29. 

Table 29. Summary of technical assessment of IX processes.

Criteria Description/Rationale 

Industrial status Large industrial operations including utilization for CBM produced 

water treatment in the Powder River Basin. 

Feed water quality bins The average TDS application range is between 500 mg/L and 7,000 

mg/L. Depending on selection of IX resin, high removals of 

monovalent and/or divalent ions and possibly metals is expected. 

Product water quality Treatment process permeate quality is dependent on feed water salinity 

and operating conditions. >93% rejection of target ions is achievable. 

Production efficiency 

(recovery) 

Product water recovery is dependent on IX resin regeneration needs, 

but recovery typically exceeds 98%. 

Infrastructure considerations This treatment process has a highly variable operational footprint, and 

may be sized for single-family point-of-use systems up to large 

municipal drinking and wastewater treatment plants. Regenerant 

storage will be required, in addition to other cleaning chemicals. 

Systems may be highly mobile, however certain systems may require 

the use of heavy machinery to relocate. 

Energy consumption Energy requirements are minimal and may only include pumping 

costs. This makes IX one of the least energy intensive processes with 

an energy demand that may be as low as 1.5 kWh/kgal(0.07 kWh/bbl) 

assuming a 200 gpm flow rate, 5 m pumping head, an 80% efficient 

pump. 
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Table 29. Summary of technical assessment of IX processes.

Criteria Description/Rationale 

Chemicals Chemical cleaning rates depend on feed water quality and IX resin 

adsorptive capacity. Resin regeneration will typically occur after 

certain product water quality specifications are exceeded. Regenerant 

solutions may require the use of HCl, H2SO4, NaOH, Na2CO3, or 

NaCl. Additional chemical disinfection may be required to mitigate 

biofouling and will typically consist of H2O2 or NaOCl cleaning 

solutions. 

Life cycle The average lifespan for anion exchange resins is about 4 to 8 years, 

while cation exchange resins may perform for 10 to 15 years [114]. 

O&M considerations Monitoring and control required for flow rates, product water quality 

and resin regeneration. 

System will likely require minimal supervisory oversight. 

Level of flexibility: Low to moderate flexibility depending on resin 

type. 

Level of robustness: IX processes are highly sensitive to fouling from 

organic materials and suspended solids. Care should be exercised to 

limit exposure of IX resin to oxidized metals and sparingly soluble 

mineral salts. Acid cation resins should not be exposed to feed 

temperatures in excess of 120 °C, while base anion resins are limited 

to 100 °C or lower. 

Level of reliability: IX systems may operate semi-continuously with 

automated, short duration resin regeneration cycles. Other IX systems 

may operate continuously for 10-20 hours and require several hours of 

downtime during regeneration. 

Types of energy required: electrical. 

Overall costs The costs for IX vary between $1.9-2.6/kgal ($0.08-0.11/bbl) at 220 

gpm (5 bbl per minute) and $1.0-1.7/kgals ($0.04-0.07/bbl) at 880 gpm 

(21 bbl per minute). At the lower flow rate, operating costs account for 

~70% of the total cost with regenerants, raw water, labor and 

maintenance making the most significant contributions. At 880 gpm, 

operating costs increase to ~80% [115]. 

Pre-and post treatment Process will require pretreatment options including suspended solids, 

oxidized metals, and scaling mineral removal. 

Product water may require pH stabilization or remineralization. This 

may be achieved by lime bed contacting or by blending small amounts 

of filtered and sterilized feed water with product water. 

Concentrate management or 

waste disposal 

The spent resin regeneration solution will require neutralization. 

Relatively high recovery rates exceeding 98% generate very minor 

amounts of concentrated brine. 

Applicability for produced 

water treatment 

Excellent – Treatment well suited for specific applications. 

Note: 1 barrel = 42 US gallons 

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Capacitive deionization (CDI) & Electronic Water Purifier (EWP) 

Capacitive deionization (CDI) is an emerging desalination technology. The Lawrence 

Livermore National Laboratory (LLNL) started studying CDI in the late 1980s. In CDI, ions are 

adsorbed onto the surface of porous electrodes by applying a low voltage electric field, 

producing deionized water (Figure 24). Liquid is flowing between the high surface electrode 

pairs having a potential difference of 1.0-1.6 Volt DC. The negative electrodes attract positively 

charged ions such as calcium, magnesium, and sodium, and the positive electrodes attract 

negatively charged ions such as chloride, nitrate, and silica. The major mechanisms related to the 

removal of charged constituents during water treatment are physisorption, chemisorption, 

electrodeposition, and/or electrophoresis. Unlike ion exchange, no additional chemicals are 

required for regeneration of the electrosorbent in this process. Adsorbed ions are desorbed from 

the surface of the electrodes by eliminating the electric field, resulting in the regeneration of the 

electrodes. The efficiency of CDI strongly depends on the surface property of electrodes such as 

their surface area and adsorption properties [116]. 

There are a variety of electrode materials and configurations to enhance the CDI 

performance. The LLNL developed and optimized carbon aerogel materials, which are ideal 

electrode materials because of their high electrical conductivity, high specific surface area, and 

controllable pore size distribution [117]. Shiue et al. improved the CDI efficiency by using spiral 

wound electrodes (activated carbon coated on titanium foil) cartridge [118]. Atlas developed the 

Electronic Water Purifier (EWP), which is a hybrid CDI and electrodeionization (CDI-EDI) 

technology using activated carbon electrodes that has a coating and a conductive material [119]. 

++++++++++++++++

----------------

Positive electrode

Negative electrode

Salty 

water

Pure 

water

DC 

power 

supply

Neutral electrode

Neutral electrode

Regeneration 

water

Concentrate

Figure 24. Schematic of Capacitive Deionization (CDI). 

Previous studies have shown that CDI technology is cost competitive to RO at low TDS 

range (<3,000 mg/L) due to the high cost of CDI modules with increased feed water TDS level 

[116, 119, 120]. Xu et al. (2008) conducted a pilot-scale testing of produced water treatment at a 

sandstone gas production field in Montana using two industrial capacitive deionization 

technology (CDTTM) aquacells developed by CDT, Inc., Dallas, TX. For the development of 
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cost-effective CDI system, the capacitance of carbon aerogel have to be improved while 

production cost should be reduced. Long regeneration time and carry-over of ions following 

regeneration limit the efficiency of treatment of highly saline water and decrease the production 

recovery [116]. The laboratory and field-testing during treatment of sandstone produced water 

indicated that CDI exhibited much less fouling/scaling propensity compared to RO/NF [116]. 

CDI required a simple cartridge filtration as pretreatment, and no electrode deterioration was 

observed during both laboratory and field-testing of produced water. 

Atlas tested the Electronic Water Purifier (CDI-EDI) for CBM produced water treatment 

in the Atlantic Rim (Washakie Basin), Carbon County, Wyoming [119]. A picture of the EWP 

unit is shown in Figure 25. The system is mounted in a 6’x8’x8’ (WxLxH) container, and can be 

transported easily to different sites. The test was conducted with feed flows of 5 gpm (1000 

bbl/day) and with two 5-gpm systems in series. Solids were filtered using a 30-micron filter. The 

field testing results are summarized in Table 30. The technical assessment of the EWP produced 

water treatment technology is summarized in Table 31. 

Table 30. Field testing results of treating CBM produced water (Source: [119]) 

Feed Conductivity 2,500 mg/L 

Purified Effluent 270 mg/L 

Estimated Feed SAR 24 

Estimated Product SAR 3 

Purification average 90% 

Recovery 85% 

Power Consumption 4.0 kWh/kgal (0.17 kWh/bbl) 

Figure 25. Electronic Water Purifier Pilot Test--250 BPD (Source: [119]). 
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Table 31. Summary of technical assessment of EWP process. 

Criteria Description/Rationale 

Industrial status Emerging technology. Have been pilot tested in Atlantic Rim for CBM 

produced water treatment 10, 000 gal/day (250 bbl/day). 

Feed water quality bins Cost competitive for water with TDS <3,000 mg/L. Has been applied to 

medium TDS range (<6,000 mg/L). CDI is applicable to all types of water 

chemistry makeup. 

Product water quality Product water quality depends on treatment time. EWP can achieve 90% 

TDS removal. CDI has poor removal of uncharged substances such as 

boron and organics. 

Production efficiency 

(recovery) 

Product water recovery is approximately 80%. 

Infrastructure 

considerations 

Very low infrastructure requirement. Small footprint and mobile. 

Energy consumption The power consumption of CDI depends on the amount of salt removed. 

For example, to achieve 88-89% removal, the energy consumption of EWP 

is 4 kWh/kgal (0.17 kWh/bbl) for 2,500 mg/L TDS feed water, and 18 

kWh/kgal (0.76 kWh/bbl) for 6,000 mg/L TDS water [119]. 

Chemicals No chemicals required. 

Life cycle Expected 10 years. 

O&M considerations Low levels of monitoring and control. 

Low level of skilled labor required. 

High level of flexibility. 

High level of robustness. 

High level of reliability. 

Types of energy required: electricity or gas. Can be run by 3 kW diesel, 

propane generator also available. 

Overall costs Over a 10-year span the total cost of capital and operations is estimated 

$0.05 per barrel of water processed [119]. 

Pre-and post treatment Minimal pretreatment such as cartridge filter. 

Concentrate management 

or waste disposal 

20% brine needs deep well injection or crystallizer for ZLD, and generated 

solid solids need waste disposal. 

Applicability in produced 

water treatment 

Good for treatment of produced water with TDS<3,000 mg/L. 

Note: 1 barrel = 42 US gallons 

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Gas Hydrates 

 Gas hydrates are crystalline water-based solids that physically resemble ice. However, 

instead of the closed crystalline lattice structure of ice, gas hydrates have open lattice structure 

with a cavity that traps non-polar molecules (typically gases). A photograph of a gas hydrate is 

shown in Figure 26. The hydrogen bonded water molecules essentially form a cage structure that 

traps gases including CH3, H2S, and CO2. An illustration of a gas hydrate is also shown in Figure 

26. As with the freeze-thaw technology, when water crystallizes, it tends to exclude impurities 

(such as dissolved salts and suspended solids) from the crystalline matrix. Stable gas hydrates are 

naturally formed at moderately high pressures (10-13 MPa) and relatively low temperatures (0-

10 °C) at natural gas seeps within marine sediments [121]. The formation and subsequent 

processing of gas hydrates produce three streams: a pure water stream, natural gas, and 

concentrated brine. 

Figure 26: The physical and chemical appearance of gas hydrates. Methane liberated from a solid 

gas hydrate (left) (Source: [122]). Open crystalline ‘cage’ structure of a gas hydrate with a green 

polar molecule ‘trapped’ inside (right) (Source: [123]). 

 A collaborative research initiative conducted by BC Technologies in conjunction with 

Oak Ridge National Laboratory (ORNL) and the International Petroleum and Environmental 

Consortium seeks to evaluate the effectiveness of forming gas hydrates in-situ at the well head 

for produced water treatment and management. The study is in its last year and is currently 

undergoing field demonstrations of an unspecified scale. Prior to the field demonstration, pilotscale experiments were performed with flowrates of 1,050 to 2,100 gpd (25 to 50 bpd) on feed 

water with similar chemistry to that identified in the Greater Green River Basin [124]. These 

experiments demonstrated that the pilot system could recover 50-60% of the hydrates in a single 

pass; yet, of the hydrates recovered, only 23-29% of the feed water volume is converted to pure 

water. The feed water is reported to be composed of a TDS concentration that is greater than 

10,000 mg/L, but is not likely to be greater than 35,000 g/L. No further data is currently 

available to assess the technical merits and limitations of this technology. 

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Evaporation 

Evaporation ponds use the natural water cycle driven by solar energy to evaporate water. 

Depending on the produced water quality, the ponds may be lined to prevent concurrent 

subsurface infiltration of the water. In other geologic settings, the ponds may be placed on 

natural confining layers such as bentonite rich clay soils, or exposed shales that prevent the 

downward migration of the groundwater [19]. If the evaporation pond is constructed solely for 

evaporative loss (no infiltration), the ponds are generally designed to be broad shallow pools that 

maximize the surface area allowing for increased evaporation rates. Once the water has 

evaporated, the salt sludge is either left in place or removed and hauled offsite for disposal. This 

disposal method can be expensive due to the large surface area required and the associated land 

and impermeable liner costs [125]. Regulatory requirements, ecological impacts, and possible 

concentration of trace elements to toxic levels may determine the design, construction, and 

operation of evaporation ponds. 

Evaporation ponds can be a viable option in relatively warm, dry climates with high 

evaporation rates, level terrain, and low land costs. They are typically economical and employed 

only for smaller concentrate flows. Evaporation rates can be enhanced by spraying the water 

through nozzles. However, this practice can lead to salt damage to soil and vegetation due to 

drifting. Therefore, misting towers are not currently recommended as a management practice 

[11]. Produced water can be managed at small onsite evaporation ponds or can be sent offsite to 

commercial facilities that employ large evaporation basins. Examples of commercial evaporation 

facilities can be found in Colorado, New Mexico, Utah, and Wyoming [1]. 

Solar energy ponds are special type of evaporation alternatives that focus on capturing 

solar energy with the goal to use it beneficially. The approach uses salinity gradients to trap 

energy in the lower, higher density layer of the concentrate in the pond. The solar energy 

penetrates the upper, less concentrated layers. The lower, heated layer does not rise due to the 

higher concentration and density and the absence of convection, and thus reaches significantly 

high temperatures. The energy trapped in this layer is extracted and can be used to generate 

electricity. Solar ponds have some concentrate volume-reducing properties but they are not a 

concentrate management process [126]. 

ALL Consulting investigated the potential of using evaporation ponds in some of the 

areas of interest for CBM development [19]. For example, the Powder River Basin (PRB) of 

Montana and Wyoming and the San Juan Basin of Colorado, evaporation rates between 28 and 

40 in/yr have been historically recorded, while areas in Utah have evaporation rates between 40 

and 52 in/yr. The Gulf Coast region of Louisiana and Texas has average evaporation rates 

between 48 and 70 in/yr. Thus in the areas where future CBM development is expected to occur, 

the potential exists for evaporation to result in a significant amount of managed water loss. 

Although some portions of these states have considerable annual evaporation, seasonal variations 

should be taken into account. 

The contaminants in produced water such as selenium, oil, and other hydrocarbons may 

pose potential problems to migratory waterfowl. Covering ponds with netting helps to avoid this 

problem [57]. The technical assessment of evaporation ponds for produced water disposal is 

summarized in Table 32. 
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Table 32. Summary of technical assessment of evaporation ponds. 

Criteria Description/Rationale 

Industrial status Industrialized technology. Have been used for produced water management. 

Feed water quality bins From low TDS range 2,000 mg/L to high TDS >40,000 mg/L. 

Product water quality Not applicable. 

Production efficiency 

(recovery) 

Concentrate management technology. All water is evaporated and hence 

“lost” to atmosphere 

Infrastructure 

considerations 

Large land area requirements. Landscape and topography are important in 

siting the location of an evaporation pond. Clay or synthetic liners are 

required. Monitoring wells or boreholes are required. 

Siting, designing, and constructing the ponds should consider minimizing 

the volume of water that is able to enter the pond from natural runoff or 

flooding. 

Energy consumption Only energy requirement is pumping of concentrate to the pond. 

Chemicals No chemicals required. 

Life cycle Depending on the projected oil/gas development 

O&M considerations Minimal; only mechanical equipment used is pumps. Other items may 

include liner repairs and monitoring. 

Overall costs Capital costs are highly variable and dependent on location. There is little 

economy of scale, and method is most competitive for small flows. 

Pre-and post treatment None except sludge disposal if pond has been designed for periodic sludge 

removal (hazardous sludge would require proper handling, treatment, and 

disposal). 

Concentrate management 

or waste disposal 

Pond may be designed for either sludge accumulation throughout life of 

ponds with capping at the end of useful life, or for periodic sludge removal 

and disposal. 

Applicability in produced 

water treatment 

Excellent for disposal of produced water, more economical and competitive 

to small flows. 

Note: 1 barrel = 42 US gallons 

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Wind Aided Intensified Evaporation (WAIV) 

The WAIV is a relatively new technology that was developed to be used in conjunction 

with evaporation ponds. It uses wind to promote evaporation and to reduce the overall surface 

area of the ponds. The concentrate is sprayed over vertical transport surfaces to reduce the pond 

footprint. The hydrophilized evaporation surfaces can consist of woven nettings, or non-woven 

geo-textiles, or tuff (vocanic rock) arranged in trays. Studies indicate that the WAIV method 

intensifies the evaporation process to about 10 times that of regular evaporation ponds [127]. The 

footprint of the WAIV ponds can be much smaller than a typical evaporation pond. The approach 

is illustrated in Figure 27. 

This technology was tested in Israel, and it is likely that it can be used in similar 

conditions of low humidity and high temperatures in CBM development areas. The US Bureau 

of Reclamation tested this technology and identified that the dripping nozzles would salt up and 

clog. This required cleaning of the nozzles on a regular basis [126]. 

Lesico CleanTech manufactures the WAIV evaporation technology [128]. The technical 

assessment of the WAIV for produced water disposal is summarized in Table 33. 

Figure 27. Schematic of Wind Aided Intensified Evaporation (WAIV) Process (Source: [93]). 
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Table 33. Summary of technical assessment of WAIV evaporation ponds. 

Criteria Description/Rationale 

Industrial status Emerging technology, pilot tested in Israel. Have not been used for 

produced water management. 

Feed water quality bins Applicable to high TDS water >20,000 mg/L. 

Product water quality Not applicable. 

Production efficiency 

(recovery) 

Concentrate management technology. All water is evaporated and hence 

“lost” to atmosphere. 

Infrastructure 

considerations 

Compact and modular system. Due to enhanced evaporation using vertically 

stacked surfaces, the area requirements are significantly reduced compared 

to evaporation pond. Area reported to be reduced about 10 times. 

Energy consumption No data available. Overall, energy consumption would be higher than for 

evaporation pond since additional pumping energy would be required. 

Chemicals Acid for cleaning of the evaporation surfaces. 

Life cycle No data available, expected to depend on the projected oil/gas development. 

O&M considerations No data available. Expected to be greater than for evaporation pond since 

more pumping, mechanical frames, and evaporation surfaces are used. 

Overall costs No cost information is reported. In general, O&M costs are expected to be 

higher as compared to evaporation pond, though comparison of capital costs 

is unknown, except that, aside from the wind parameter, capital costs for 

WAIV would be location independent while pond costs are highly variable 

and dependent on location. 

Pre-and post treatment None except sludge disposal if pond has been designed for periodic sludge 

removal (hazardous sludge would require proper handling, treatment, and 

disposal). 

Concentrate management 

or waste disposal 

Pond may be designed for either sludge accumulation throughout life of 

ponds with capping at the end of useful life, or for periodic sludge removal 

and disposal. 

Applicability in produced 

water treatment 

Good candidate for disposal of produced water. More economical and 

competitive for small flows. 

Note: 1 barrel = 42 US gallons 

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Commercial Thermal Processes 

GE: Evaporative produced water treatment and steam generation using MVC evaporators 

Steam injection is becoming a common method to enhance oil recovery during oil 

production. Thermal technologies have been used to treat produced water while generating steam 

for extracting heavy oil. Conventional produced water treatment and steam generation system 

often includes a warm or hot lime softener followed by a filtration system to reduce silica, 

calcium, and magnesium concentration in de-oiled produced water (Figure 28). The hardness 

and iron are further removed through a weak acid cation (WAC) IX process to ensure the sound 

operation of the steam generator. Once-Through Steam Generators (OTSGs), driven by natural 

gas, have been used to produce approximately 80% quality steam (80% vapor, 20% liquid) for 

injection into a well to fluidize the heavy oil [129]. In most cases, the OTSG blowdown is 

disposed by deep well injection. This stream can also be further concentrated with a ZLD brine 

concentrator and crystallizer, producing a dry solid for disposal. Some of the OTSG blowdown 

can be recycled to the softener system, but as the solids are cycled up in the system, the OTSG’s 

maintenance needs are increased. 

Figure 28. Conventional produced water treatment and steam generation system (Source: [129]). 

The more recent Steam-Assisted Gravity Drainage (SAGD) method requires 100% 

quality steam for injection. The use of OTSG for SAGD applications requires a series of vaporliquid separators to produce the requisite steam quality. As an alternative to traditional produced 

water treatment and steam generation system, GE developed an evaporative produced water 

treatment process using mechanical vapor compression (MVC) evaporators for supplying high 

quality steams to SAGD. The heat transfer coefficient for the vertical-tube, falling-film MVC 

evaporators is higher than for traditional evaporators, offering improved evaporation efficiency 

and energy savings. This arrangement, in conjunction with a proprietary brine distribution 

system, allows evaporation to occur with reduced fouling by keeping surfaces perpetually wetted 

(Figure 29). By using the MVC system, produced water treatment system is much simplified as 

shown in Figure 30. 
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Figure 29. A schematic of a vertical-tube, falling-film MVC evaporator (Source: [129]). 

Figure 30. The vertical-tube, falling-film MVC evaporation system for produced water treatment 

and steam production (Source: [129]). 

De-oiled produced water enters a feed tank where the pH is adjusted. The wastewater is 

pumped to a heat exchanger that raises its temperature to a boiling point. Hot, de-aerated feed 

enters the evaporator sump, where it combines with the recirculating brine slurry. The slurry is 

pumped to the top of a bundle of heat transfer tubes. As the brine flows down the tubes, a small 

portion evaporates and the rest falls into the sump to be recirculated (Figure 29). The vapor 

travels down the tubes with the brine and is drawn up through specially designed mist 

eliminators on its way to the vapor compressor. Compressed vapor flows to the outside of the 

heat transfer tubes, where its latent heat is given up to the cooler brine slurry falling inside. As 

the vapor loses heat, it condenses as distilled water. The distillate is pumped back through the 

heat exchanger, where it gives up sensible heat to the incoming wastewater. A small amount of 

the brine slurry is continuously blowdown from the evaporator to control density [129]. 
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The OTSG or drum boiler blowdown can be recycled to the evaporator feed, eliminating 

the need to dispose of this waste stream without affecting recovered water quality. The 

evaporator blowdown is disposed via deep well injection or treated further by a crystallizer to 

eliminate all liquid waste. The crystallizer produces a dry cake material for disposal ([129]). 

Evaporative produced water treatment was tested in 1999, and was initially used by Japan 

Canada Oilsands and PetroCanada, respectively. The blowdown from the OTSG steam 

separators was effectively processed by an evaporator and crystallizer combination in a ZLD 

system. Today, there are about 16 produced water evaporators operating or under construction in 

nine plants in Alberta, Canada and other regions ([129]). 

As compared to the conventional oil produced water treatment, the evaporative produced 

water treatment exhibits a number of advantages [130]. These include: 

 Evaporators de-couple the produced water system from the boiler feed system, 

increasing boiler reliability 

 Lower capital, operating, and lifecycle costs compared to traditional method 

 Eliminates traditional produced water treatment systems (WLS or HLS, WAC, etc.) 

 Minimizes softener sludge and other waste streams requiring disposal 

 Minimizes chemical use, cost, storage, and handling 

 May reduce amount of de-oiling equipment 

 Reduces maintenance materials and labor 

 Reduces ZLD system size by 80% (if ZLD is required) 

Although fouling severity and frequency have been minimal in operating produced water 

evaporators, there is a risk that severe fouling could limit steam production. The traditional 

approach eliminates this risk [129]. Due to the high energy-consumption and economical scale of 

treatment plant, the thermal technologies are more competitive for high TDS water and 

centralized treatment systems. The technical assessment of the evaporative produced water 

treatment technology is summarized in Table 34. 

Table 34. Summary of technical assessment of GE – evaporative produced water 

treatment using MVC evaporators. 

Criteria Description/Rationale 

Industrial status Mature and robust technology. Have been used for oil produced water 

treatment and steam generation. 

Feed water quality bins Applicable to a wide TDS range (<100,000 mg/L TDS), and all types of 

water chemistry makeup. 

Product water quality Product water quality for MVC is high, with little variation due to feed 

or concentrate salt content [129]. 

Production efficiency 

(recovery) 

Product water recovery is approximately 98%. 2% blowdown can be 

disposed via deep well injection or treated by a crystallizer to ZLD. 

Infrastructure 

considerations 

Infrastructure considerations are similar to MSF and MED units. 
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Table 34. Summary of technical assessment of GE – evaporative produced water 

treatment using MVC evaporators. 

Criteria Description/Rationale 

Energy consumption The power consumption of MVC evaporator is 70 kWh/kgal of 

distillate produced (2.94 kWh/bbl) [129]. A typical produced water 

evaporator will consume 60-65 kWh/kgal of distillate. The higher 

consumption of the GE MVC evaporator is that the system was 

designed to have a crystallization device downstream and, therefore, the 

cycles of concentration are higher than would otherwise be required. 

The higher cycles of concentration increase the vapor compressor 

electrical consumption to overcome the associated increase in boiling 

point of the brine within the evaporator. Electrical consumption of less 

than 60 kWh/k gal can be achieved by modifying the evaporator 

configuration [129]. 

Chemicals Scale inhibitor and acid may be required for process control to prevent 

scaling. Corrosion control is achieved via pH control. Annual cleaning 

is typically conducted using acid, EDTA, or other antiscalant. 

Life cycle Expected 30 years. 

O&M considerations Levels of monitoring and control: required for feed pH, flow rates as 

well as steam and vessel pressures. 

High level of skilled labor required. MVC is a complex system and 

adds to the O&M skill level required. 

Level of flexibility: easy to adapt to highly varying water quality but 

not flexible for varying water flows. 

Level of robustness: high ability of the equipment to withstand harsh 

conditions. 

Level of reliable: typical plants operate continuously, with 99% onstream availability. 

Types of energy required – electricity and gas. 

Overall costs Economic comparisons of produced water treatment approaches are site 

specific and detailed conclusions will vary. However, there is a 

consensus in the industry that the majority of new SAGD facilities will 

use evaporative treatment methods, with a minority continuing to 

utilize traditional methods. 

Pre-and post treatment MVC requires minimal pretreatment such as de-oiling, pH adjustment, 

and deaeration. 

Concentrate management 

or waste disposal 

2% brine needs deep well injection or crystallizer for ZLD, and 

generated solid solids need waste disposal. 

Applicability in produced 

water treatment 

Excellent technology for produced water with high TDS and near ZLD 

disposal, more applicable to centralized system and large flow rate. 

Note: 1 barrel = 42 US gallons 

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Aquatech: Mechanical Vapor Compression (MVC) Technology 

Aquatech International Corporation develops membrane/thermal technologies to address 

the needs of diverse industries, including power, oil and gas, mining, and metals. Aquatech 

offers diverse products that encompass various water and wastewater treatment technologies 

under the WATERTRAKTM umbrella. It includes RO, RECOMAXTM, HEROTM and UF (both 

tubular and hollow fiber), IX, electrodeionization, media filters, and activated carbon filters. 

Aquatech uses MVC technology to provide high recoveries to minimize the requirement for 

fresh water such as for the Canadian Tar Sands by allowing efficient reuse of oilfield produced 

water (Source: www.aquatech.com). 

No enough data allow a technical assessment for Aquatech MVC technology. However, it 

is expected to be similar to the GE MVC technology as shown in Table 34. 

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Aqua-Pure - Mechanical Vapor Recompression (MVR) Evaporation 

 The NOMAD systems are designed and built by Aqua-Pure Ventures Inc., based in 

Calgary, Alberta, Canada, and operated by Granbury-based Fountain Quail Water Management. 

This MVR evaporation NOMAD system is an energy efficient process that uses a very compact 

welded cassette heat exchanger with a plate-and-frame construction and a rising-film design. 

With this design, boiling occurs on a wet surface, minimizing scale deposition that occurs in 

conventional thermal technologies. 

For frac flowback water treatment, feedwater is first dosed with flocculants to 

coagulate/flocculate the suspended solids and organic matters. The wastewater is then passed 

through an inclined plant mechanical separator to remove formed flocs. The effluent from the 

separator is pumped to the Aqua-Pure MVR evaporator unit to remove dissolved solids (Figure 

31). A compressor is used to add the energy required to boil water. The feed water passes 

through two preheat exchangers where heat is absorbed from the distillate and concentrate 

products leaving the system. The feed then passes into a recirculation loop where concentrate 

circulates through an evaporator exchanger and a vapor / liquid separator. A portion of the 

concentrate is boiled to steam in the evaporator exchanger and separated from the liquid in the 

separator vessel. 

The manufacturer claims that the MVR evaporation can recycle up to 85% of frac 

flowback water into distilled water. With a lower contamination level in the feed water, the 

system could achieve a 90% to 95% recovery of distilled water [131]. The treated water is stored 

in tanks for future reuse. 

The system is skid mounted. The footprint of the MVR system NOMAD 2000 is similar 

to that of a traditional MVR evaporator—about 2,500 square feet for a daily output of 84 kgal 

(2,000 barrels) of distilled water and 21 kgal (500 barrels) of concentrated brine. The system 

consists of three modules, each 11.5 feet wide and 12.5 feet high [131]: 

• A pre-treatment module 40 feet long, weighing 25,000 pounds. 

• An evaporator module 37 feet long, weighing 42,000 pounds. 

• A compressor module 30 feet long, weighing 96,000 pounds. 

The system also includes interconnecting pipes and electrical connections, and a 50-kW 

generator. It needs no external source of electric power. It draws natural gas directly from the 

well to run the compressor and to drive the generator, which produces electricity to power the 

pumps, instruments, and controls. Figure 32 shows a close view of the Aqua-Pure unit operating 

by Devon Energy Corporation near Decatur, Texas. 

A summary of the technical assessment of Aqua-Pure MVR Evaporation process based 

on the information provided in the manufacturer’s website is listed in Table 35. 
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Figure 31. Schematic of the Aqua-Pure MVR Evaporator (Source: [131]). 

Figure 32. Closer view of the Aqua-Pure unit (Source: J. Veil, Argonne National Laboratory). 

Table 35. Summary of technical assessment of Aqua-Pure MVR Evaporation process. 

Criteria Description/Rationale 

Industrial status Pilot-scale field-testing for frac water treatment. 

Feed water quality bins Applicable to TDS <80,000 mg/L, and a broad variety of water chemistry 

makeup. 

Product water quality Product water quality is very high with TDS in the range of 10 mg/L [132]. 

Trace amounts of volatile hydrocarbons may present. 

Production efficiency 

(recovery) 

Product water recovery is between 60 and 90%, depending on feed water 

quality (Source: NOMAD 2000 Factsheet). 
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Table 35. Summary of technical assessment of Aqua-Pure MVR Evaporation process. 

Criteria Description/Rationale 

Infrastructure 

considerations 

No special infrastructural requirement as the unit is skid-mounted. The 

footprint of NOMAD 2000 is 2,500 square feet. Require gas or electricity as 

power. 

Energy consumption The energy consumption should be comparable to the pressure distillation 

methods such as MVC, about 30 kWh/kgal (1.3 kWh/bbl) of product water. 

Operational energy use is 466 KW for the NOMAD 2000 unit. 

Chemicals Flocculants for coagulation and flocculation. Similar to other thermal 

technologies, scale inhibitor and acid may be required for process control to 

prevent scaling. Corrosion control is achieved via pH control. Annual cleaning 

is typically conducted using acid, EDTA, or other antiscaling chemicals. 

Life cycle Typically expected 20 years, although longer life may be expected with the 

selection of better materials of construction, that is, alloys with high corrosion 

resistance [93]. 

O&M considerations Low level of monitoring and control required for feed pH, flow rates as well as 

steam and vessel pressures. 

High level of skilled labor required to operate MVR evaporators. 

High level of flexibility: easy to adapt to highly varying water quality and 

quantity. 

High level of robustness: high ability of the equipment to withstand harsh 

conditions. 

High level of reliability: scale removal requires a two-man crew in one or two 

work shifts, less than with a traditional MVR evaporator. 

Types of energy required – Gas or electricity. 

Overall costs According to Devons, the cost to treat frac water is $79.6/kgal ($3.35/bbl), 

about 68% more than the $47.6/kgal ($2/bbl) cost if post-fracing water is 

simply disposed of [133]. Devon has continued to study the Aqua-Pure process 

for its potential payoffs in the future, both in the Barnett Shale region and 

elsewhere. They are gaining valuable experience with the technology and can 

work on improving its efficiency and lowering the cost (Source: John Veil, 

Argonne National Lab). 

In the Barnett Shale region, natural gas is plentiful, and can be readily obtained 

as a fuel source to operate the technology. In other applications, such as 

treating produced water from oil wells, natural gas may not be an affordable 

energy source (Source: John Veil, Argonne National Lab). 

Pre-and post treatment Require pre-treatment to remove suspended solids and organic matter. Product 

water needs remineralization because of the low TDS level. This may be 

achieved by lime bed contacting or by blending small amounts of filtered and 

sterilized feedwater with the distillate. Post-treatment may also include carbon 

adsorption or oxidation if organic substances are present in product water. 

Concentrate 

management or waste 

disposal 

Solids collected in the separator need a filter press for dewatering and disposal. 

The brine stream needs transported off the well site and then injected into a 

disposal well or evaporated/stored in large ponds.

Applicability in 

produced water 

treatment 

Good candidate technology for produced water with high TDS and near ZLD 

disposal, more applicable to centralized system and large flow rate. 

Note: 1 barrel = 42 US gallons 

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212 Resources - Mechanical Vapor Recompression (MVR) Evaporation 

 Similar to Aqua-Pure MVR evaporation process, 212 Resources developed and operates 

transportable, skid-mounted "pods" that deployed at drill site to process frac flowback water for 

reuse (www.212resources.com). The treatment train consists of a number of process elements 

(Figure 33), including: 

 Collection and gravity settling of solids 

 Course filtration and material management 

 Heated oil/water separation to recover immiscible hydrocarbons 

 Vapor compression, turbulent flow, high velocity flash evaporation to recover brine 

and distilled water 

 Steam distillation integrated with the evaporator for recovery of methanol and other 

miscible hydrocarbons with advanced UV and carbon filtration polishing 

 The units are powered by natural gas from the local site or from external electrical 

hook-ups 

Its core technology is a patented VACOM technology (http://www.vacomllc.com/) that 

combines mechanical vapor recompression with turbulent flow heat exchange technology. The 

Vacom vapor compression, flash evaporation system is applicable for high TSD waters from 

deep-well, hydraulic fracing, natural gas wells, deep coalbed methane wells, and other oil and 

gas produced waters. 212 Resources’ system is able to recover oil, methanol, total dissolved 

solids, minerals, and metals from water that are associated with drilling and production. 

212 Resources has a contract to build a large plant in Wyoming for treatment of frac 

flowback water and produced water from natural gas fields [134]. In May 2008, 212 Resources 

announced that the company had signed a contract with Denver-based Delta Petroleum 

Corporation for managing its flowback and produced water in the Colorado Vega field. This ten 

year service contract involves multiple 212 Resources “pods” and is similar to the work being 

done in Wyoming, except that the treated water will be discharged off-site (the Wyoming project 

water is reused for drilling) [135]. 212 Resources has also been planning testing in the Barnett 

Shale [133, 136]. 

There are similarities in the Aqua-Pure (or Fountain Quail) and 212 Resources systems: 

both can be powered by on-site natural gas and both use evaporation and distillation 

technologies. The 212 Resources system uses a different method of heat transfer, allowing the 

machines to handle higher TDS (110,000 mg/L) than the Aqua-Pure (TDS 80,000 mg/L). 

Although 212 Resources’ pods are transportable, they resemble a miniature recycling plant in an 

enclosed building when assembled. The size of a pod is 40’x60’. The Aqua-Pure’s NOMAD 

system serves as a transportable and modular technology with a 20’x60’ footprint. A summary of 

the technical assessment of the 212 Resources’ process is listed in Table 36. 
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Figure 33. Schematic of the 212 Resources water treatment system (Source: [137]). 

Table 36. Summary of technical assessment of the 212 Resources water treatment system.

Criteria Description/Rationale 

Industrial status Full-scale application for frac water treatment in Wyoming and Colorado. 

Feed water quality bins Applicable to TDS <110,000 mg/L, and a broad variety of water chemistry 

makeup. 

Product water quality Similar to other MVR technology, product water quality is expected high with 

TDS in the range of 10-100 mg/L. Trace amounts of volatile hydrocarbons 

present in desalted water can be removed by carbon filtration. 

Production efficiency 

(recovery) 

Product water recovery is between 90 and 95%, depending on feed water 

quality. 

Infrastructure 

considerations 

No special infrastructural requirement as the unit is skid-mounted. The 

footprint of pods is 40’x60’. Require gas or electricity as power. 

Energy consumption The energy consumption is expected to be comparable to the pressure 

distillation methods such as MVC, about 30 kWh/kgal (1.3 kWh/bbl) of 

product water. 

Chemicals Similar to other thermal technologies, scale inhibitor and acid may be required 

for process control to prevent scaling. Corrosion control is achieved via pH 

control. Annual cleaning is typically conducted using acid, EDTA, or other 

antiscaling chemicals. 

Life cycle Typically expected 20 years, although longer life may be expected with the 

selection of better materials of construction, that is, alloys with high corrosion 

resistance [93]. 

O&M considerations High level of monitoring and control required for feed pH, flow rates as well as 

steam and vessel pressures. 

High level of skilled labor required to operate MVR evaporators. 

High level of flexibility: easy to adapt to highly varying water quality and 

quantity. 

High level of robustness: high ability of the equipment to withstand harsh 

conditions. 

High level of reliability. 

Types of energy required: Gas or electricity. 
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Table 36. Summary of technical assessment of the 212 Resources water treatment system.

Criteria Description/Rationale 

Overall costs The cost of treating the frac flowback water is not reported. However the costs 

persuaded the industry to employ the technology to treat the frac water. It is 

assumed that the cost of 212 Resources technology is competitive to the AquaPure process. Besides, the recovered oil and methanol can bring additional 

profits. 

Pre-and post treatment Pre-treatment includes settling and filtration to remove suspended solids and 

organic matter. 

Product water includes UV and carbon filtration to remove miscible 

hydrocarbons. Remineralization or blending may be required depending the 

application of product water. 

Concentrate 

management or waste 

disposal 

The solids collected in the separator need a filter press for dewatering, and then 

disposal. 

The brine stream needs transported off the well site and then injected into a 

disposal well or evaporated/stored in large ponds. 

Applicability in 

produced water 

treatment 

Excellent technology for produced water with high TDS and near ZLD 

disposal, more applicable to centralized system and large flow rate. 

Note: 1 barrel = 42 US gallons 

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AGV Technologies: Wiped Film Rotating Disk (WFRD) 

AGV Technologies, Inc. (AGV) developed a new Wiped Film Rotating Disk (WFRD) 

system for produced water treatment. The WFRD is a vapor-compression distillation technology 

that can also operate in the MED mode if thermal energy is available [138]. The WFRD system 

uses rotating disks as heat transfer surfaces. A thin microfilm layer of input water (produced 

water) is applied to the outside surface of the rotating disk. Superheated vapor in the cavity of a 

disk condenses on the inside surface. A slight temperature difference across this disk allows heat 

to flow from the condensing liquid to the evaporating fluid, driving evaporation and recycling of 

the latent heat of evaporation. This evaporated vapor moves to the next disk assembly (effect) 

and is condensed, providing the energy to evaporate more feed water [138]. A schematic for a 

five-effect WFRD unit operating in the vapor compression mode is illustrated in Figure 34. 

Figure 34. Schematic flow diagram for a five-effect WFRD unit operating in the vapor 

compression mode with each slanted line representing the rotor in each of the five effects [138]. 

AGV Technologies claims that the WFRD is designed to improve heat transfer efficiency 

and reduce scaling and fouling [138]. Resistance to heat flow in distillation is determined by the 

thickness of the liquid layer on the evaporation and condensation surfaces. The WFRD design 

minimizes this thickness; resulting in very thin condensate and feed films on the heat transfer 

surfaces. The WFRD technology achieves a heat transfer coefficient of 25 kW m-2 °C-1. 

In 2004, the WFRD technology was tested using CBM production water collected from 

two sources – the Powder River Basin (Northeast Wyoming / Southeast Montana, with TDS 

1,068 mg/L) and the San Juan Basin (New Mexico, with TDS 23,000 mg/L). Produced water 

from each source was treated using a prototype WFRD test unit; a single effect system with two 

24-inch disk sets. It was configured to operate at an 8 to 1 brine recycle ratio and an evaporator 

temperature of 122 °F. The system is capable of producing a maximum of 2.6 gal per hour. Each 

run processed 5 gallons of produced water with recovery rate of 90%. The AGV technology 

removed 99% of the TDS from both raw produced waters without any adjustments, pretreatment, 

or additional equipment. TOC was reduced by 86% for the San Juan samples and 70% for the 

Powder River samples. While the percentage reduction for some inorganic constituents and TOC 
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resulting from WFRD processing was less in the Powder River samples, the levels measured in 

Powder River recovered water were very low [138]. 

Currently, AGV Technologies, Inc. is developing the PW-600 – the first commercial 

AGV product. It will be available for installation in oil and gas production and produced water 

disposal facilities. The PW-600 system is designed to process 25 kgal (600 barrels) of produced 

water per day. Initial PW-600 units are electrically powered. Waste heat, cogeneration, and 

renewable energy powered models will be available. 

The WFRD system has been proved promising through the short-term laboratory testing. 

Long-term testing would be required to demonstrate its performance and efficiency in production 

field. The assessment summarized in Table 37 is based on test operation of the prototype system 

and results presented in the 2004 Final Report “Improving Produced Water Quality for Coal Bed 

Methane. Prepared by AGV Technologies, Inc. for RPSEA” [138]. 

Table 37. Summary of technical assessment of the WFRD distillation system.

Criteria Description/Rationale 

Industrial status Emerging technology in produced water treatment. Has been previously 

employed for CBM produced water treatment at bench-scale (capacity 2.6 

gallons per hour). Currently the vendor, AGV Technologies, Inc. is 

developing a commercial unit treating 600 bpd of produced water. 

Feed water quality bins Applicable to TDS range from 1000 to 23, 000 mg/L. 

Product water quality TDS rejection 99%; TOC rejection 70- 86%; ammonia rejection low. 

Production efficiency 

(recovery) 

Product water recovery is approximately 90%. 

Infrastructure 

considerations 

No special infrastructural requirement as the unit is skid-mounted. The 

system requires housing or shed. Energy sources could be gas, electricity, 

thermal, and renewable energies. 

Energy consumption Not available. 

Chemicals It is expected that scale inhibitor and acid may be required for process 

control to prevent scaling. Corrosion control is achieved via pH control. 

Annual cleaning is typically conducted using acid, EDTA, or other 

antiscaling chemicals. 

Life cycle Not available. 

O&M considerations High level of monitoring and control required for feed pH, flow rates as 

well as steam and vessel pressures. 

High level of skilled labor required to operate distillation system. 

High level of flexibility: easy to adapt to highly varying water quality and 

quantity. 

High level of robustness: high ability of the equipment to withstand harsh 

conditions. 

High level of reliability. 

Overall costs Not available. AGC Technology estimates that the operational cost of 

processing produced water with the WFRD will be approximately 30% of 

that for the distillation systems ($0.67/bbl). If powered with thermal energy 

from a methane-fired boiler, the operating cost would be reduced 45% 

compared with the electrically powered WFRD. A cogeneration 

configuration results in a 67% cost reduction compared with electrically 

powered WFRD configuration. 
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Table 37. Summary of technical assessment of the WFRD distillation system.

Criteria Description/Rationale 

Pre-and post treatment Pre-treatment might includes settling and filtration to remove suspended 

solids and organic matter. 

Product water includes UV and carbon filtration to remove miscible 

hydrocarbons. Remineralization or blending may be required depending the 

application of product water. 

Concentrate management 

or waste disposal 

The 10% brine stream needs disposal, such as deep well injection or using 

solar ponds. 

Applicability in produced 

water treatment 

Similar to other thermal technologies, the WFRD is a good candidate to 

treat high salinity produced water. 

Note: 42 gallons in a barrel. 

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Intevras Technologies, LLC: Evaporative Reduction and Solidification (EVRAS) units 

Intevras Technologies, LLC, a Texas privately held company, has developed a thermal 

method for brine treatment called EVRAS (Evaporative Reduction and Solidification). The 

EVRASTM system is a patented technology that utilizes low-grade waste heat to concentrate 

and/or crystallize large volume wastewater streams. 

The EVRAS technology employs an evaporative process similar to a cooling tower that 

relies on water temperature, surface area, and airflow. Produced water evaporates during the 

process into the atmosphere. The EVRASTM "crystallizers" allow total evaporation, resulting in 

precipitated solids. The solid waste residue is then removed for disposal, re-cycling, or resale 

(salts) in other markets. 

The EVRAS system overcomes the scaling problems on heat exchangers through the use 

of (i) flexible films as the surface media for the air and brine contacting process, and (ii) two step 

heat transfer process employing an intermediary heat transfer liquid. A schematic of the EVRAS 

process is illustrated in Figure 35. 

Figure 35. Schematic of EVRAS process for brine treatment (Source: [139]). 

The EVRAS system is being tested in produced water field for brine volume 

minimization. For example, as part of a joint pilot project with the City of Fort Worth, 

Chesapeake Energy is studying the EVRAS system as a potential way to reduce the amount of 

produced water being injected into saltwater disposal wells in the Barnett Shale. A picture of the 

EVRAS system is shown in Figure 36. Using the heat generated by natural gas compressor 

stations (an energy source that would typically being wasted), the system filters and then 

evaporates a portion of the produced water into atmosphere. Early estimates indicate that 

approximately 50 kgal (1,200 barrels) of fresh water can be evaporated out of 126 kgal (3,000 

barrels) of concentrated saltwater, resulting in smaller volume to be injected [140]. 
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According to the technical information provided in the website of Intevras Technologies, the 

advantages of the EVRAS system include: 

 Use of low temperature waste heat 

 TDS insensitive 

 Corrosion resistant and minimal scaling problems 

 Simplicity in operation and minimal maintenance: operating at atmospheric pressure 

 No blow-down or discharge 

The EVRAS process is an evaporative system and no fresh water is recovered from 

produced water. The EVRAS fits with compression stations to use the waste heat. Without waste 

heat available onsite, the process is energy intensive and may not be feasible for CBM produced 

water treatment. The EVRAS system does not have multiple effects; therefore, the energy 

consumption is intense. Also, the vendor claim that the EVRAS system is suitable to treat large 

volume of waste streams and it may not be feasible to treat point source of CBM produced water 

with varying flow rates. The assessment summarized in Table 38 is based on the information 

provided in the website of Intevras Technologies, LLC (www.intevras.com). 

Figure 36. Picture of an EVRAS system to evaporate a portion of produced water from natural 

gas drilling in Barnett Shale [140]. 

Table 38. Summary of technical assessment of the EVRAS evaporative system. 

Criteria Description/Rationale 

Industrial status Proven technology in various industries. For example, the technology has 

been employed in California for waste disposal of brines generated with the 

production of oil and gas. It is also being tested for reducing the produced 

water volume during natural gas drilling in the Barnett Shale (field testing, 

capacity unknown). Intevras Technologies, LLC, owns the patent of the 

technology. 

Feed water quality bins The technology is not sensitive to the level and type of brine. The process 

has been employed with saturated feed waters at TDS level of 310,000 

mg/L [141]. 

Product water quality No product water. 
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Table 38. Summary of technical assessment of the EVRAS evaporative system. 

Criteria Description/Rationale 

Production efficiency 

(recovery) 

Not applicable. 

Infrastructure 

considerations 

No special infrastructural requirement. The system requires no housing or 

shed. Energy can be waste heat. Waste heat sources of 85 oF or higher are 

generally recommended. 

Energy consumption Not available. 

Chemicals The use of chemicals is expected to be minimal because of low scaling and 

fouling potential on heat exchangers. 

Life cycle Not available. 

O&M considerations Low level of monitoring and control. 

Low level of skilled labor required to operate the system. 

High level of flexibility: easy to adapt to highly varying water quality. 

High level of robustness: high ability of the equipment to withstand harsh 

conditions. 

High level of reliability. 

Overall costs Not available. 

Pre-and post treatment Minimal pre-treatment, might includes settling and filtration to remove 

suspended solids and organic matter. 

Concentrate management 

or waste disposal 

The concentrated brine stream, or solids needs disposal. The salts may be 

used for industrial applications. 

Applicability in produced 

water treatment 

The technology may be a candidate for ZLD of high salinity produced 

water. May not be cost effective to low water flow. 

Note: 1 barrel = 42 US gallons 

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Total Separation Solutions: SPR – Pyros 

Total Separation Solutions, LLC (TSS) developed a new PYROSTM system for heating 

and evaporation of produced water. Fluid is pumped into the PYROSTM system, heated to 

evaporation temperatures, and concentrated. The byproduct of the process is clean steam that is 

condensed into fresh water by heating the incoming fluid. A methodology the TSS proposed for 

produced water treatment is shown in Figure 37. 

The PYROSTM system includes cross-flow filtration modules to remove suspended solids 

from produced water and frac flowback waters. Cross-flow filtration using sintered metal tubes 

allows the continuous operation without replacing filters. The PRROSTM is part of a modular 

system. TSS, LLC claims that the complete PYROSTM system does not require any additional 

services. The modular skid design and small size allows it to be installed at the point of source of 

produced water to eliminate excessive trucking costs [142]. 

The core technology of the PYROSTM system is ShockWave PowerTM reactor (SPRTM). 

Fluid is delivered into a SPRTM reactor, where it is passed over the generator's spinning cylinder. 

The specific geometry of the holes in the cylinder, clearance between the cylinder, and the 

housing and rotational speed create pressure differences within the liquid where cavitation 

bubbles form and collapse. These collapsing microscopic bubbles generate shock waves that are 

used to heat, concentrate, and mix the fluid. The result is the conversion of mechanical energy 

into heat energy. In the SPRTM reactor, there are no heat transfer surfaces; therefore, scaling is 

not a problem. Additionally, there is an ultrasonic cleaning effect that occurs on the metal 

surfaces inside the SPRTM as the shockwaves are generated within narrow clearances. This 

cleaning effect, in conjunction with a negative temperature difference between metal and liquid, 

results in scale-free heating. 

Figure 37. Schematic of PYROS system for produced water treatment (Source: [142]). 

TSS technology has been used to process more than 10,000 bbl of frac water per day for 

an operator in the Haynesville Shale. The assessment summarized in Table 39 is based on the 

information provided on the website of TSS. 
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Table 39. Summary of technical assessment of the PYROS evaporative system.

Criteria Description/Rationale 

Industrial status SPR is a proven technology in heating fluid. It is a new technology for 

produced water treatment. It has been employed to treat frac water in 

Haynesville Shale, 10,000 bpd. TSS owns the patent of the technology in oil 

and gas field. 

Feed water quality bins The technology is not sensitive to the level and type of brine. It is expected 

to treat high TDS water. 

Product water quality High product water quality, volatile compounds can present in product 

water (steam). 

Production efficiency 

(recovery) 

The PYROS 4 system evaporates up to 5000 bbl of water, and generates 

5000 pounds of steam per hour, that is 6.8% water recovery (through 

steam), and 93.2% as concentrate. 

Infrastructure 

considerations 

Modular skid, SPR skid 8.5 x 14 feet. 

Energy consumption The system consumes 33 gallons of diesel per hour. 

Chemicals The use of chemicals is highly dependent upon the water quality. The 

chemical consumption of SPR reactor is expected to be minimal because of 

low scaling and fouling potential on heat exchangers. 

Life cycle Not available. 

O&M considerations Low level of skilled labor required to operate the system. 

High level of flexibility: easy to adapt to highly varying water quality. 

Overall costs Not available. 

Pre-and post treatment Pre-treatment might include chemical precipitation, settling, and filtration to 

remove iron and manganese, suspended solids and organic matter. 

Concentrate management 

or waste disposal 

The concentrated brine stream needs disposal or reuse. 

Applicability in produced 

water treatment 

The technology may be a candidate for treatment of high salinity produced 

water. 

Note: 1 barrel = 42 US gallons 

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Commercial IX Processes 

EMIT: Higgins Loop 

EMIT Higgins Loop technology is the most widely utilized IX process for CBM 

produced water treatment. EMIT currently has 18 operating treatment units in Wyoming, 

Montana, and Colorado. 17 of the operating treatment units are located in the Powder River 

Basin, while one system is located in the southern most area of the Greater Green River Basin 

[143]. These treatment units have a reported treatment capacity of 336,000 to 1,176,000 gpd 

(8,000-28,000 bpd) [144]. 

The Higgins Loop operates as a continuous countercurrent ion exchange contactor for 

liquid phase separations of ionic components, primarily sodium. The unique aspect of the 

Higgins Loop is that it performs resin regeneration continuously during the process, with 

minimal need for system downtime during regeneration. The IX contactor consists of a vertical 

cylindrical loop that contains a packed bed of resin separated into four operating zones by 

butterfly or "loop" valves. These operating zones are illustrated in Figure 38, and include pulsing 

(‘A’), regeneration (‘B’), adsorption (‘C’), and backwashing zone (‘D’). Each zone functions as 

a separate vessel. 

Figure 38. Schematic of the EMIT Higgins Loop IX contactor. Process diagram shows flow 

during normal operation (ion exchange service) and during resin regeneration (resin pulsing). 

Produced water containing high concentration of sodium is fed into the adsorption zone 

of the Higgins Loop. There, it contacts strong acid cation resin, which accepts Na and other 

cations in exchange for hydrogen ions. Data from field trials indicates sodium removal of 97% 

[45]. In the lower section of the Higgins Loop, resin saturated with sodium is regenerated with a 

4.11 M HCl solution (representing 1-10% of the treated volume) [143, 144]. This generates a 

small to moderate concentrated NaCl brine stream, which is typically disposed of by Class I or II 

deep injection wells. Regenerated resin is rinsed with water prior to reentry into the adsorption 

zone to remove acid from its pores. As resin in the upper layer of the adsorption zone becomes 
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loaded with sodium, the flows to the Higgins Loop are momentarily interrupted. This allows 

advancement of the resin bed (pulsing) through the loop in the opposite direction of liquid flow. 

Liquid flows are restarted after resin pulsing is complete [143, 144]. 

Higgins Loop technology is best suited for feed water containing 3,500 mg/L TDS and 

dominated by NaHCO3 [143]. Emit Higgins Loop model 3012 is built on two skids with a total 

footprint of 220 ft2

, while the more popular model 6024 ships on three skids and has a total 

footprint of 450 ft2

 [145].System setup requires a large crane (shown in Figure 39), but is 

otherwise relatively mobile. 

Figure 39. Installation of EMIT Higgins Loop system in the Powder River Basin (Source: [145]). 

Electric power consumption is estimated between 4.96 to 12.4 kWh/kgal (0.21 to 0.52 

kWh/bbl) [144]. Public data concerning operational costs is unavailable at this time, however 

this costs will likely be similar to conventional IX processes as described in Table 29. System 

life cycle and IX resin life are also not reported, however EMIT claims that the system is able to 

operate with greater than 98% runtime [143]. Field testing data shows that the Higgins Loop is 

able to achieve 98% reduction SAR values, but may not treat TDS to an acceptably low level for 

discharge of product water with current NPDES regulations [45, 143]. Further post-treatment 

may be necessary. A summary of the technical assessment for the EMIT Higgins Loop IX 

process is shown in Table 40. 

Table 40. Summary of technical assessment of EMIT Higgins Loop IX process.

Criteria Description/Rationale 

Industrial status 18 installations currently treating CBM produced water in the Powder 

River Basin and Greater Green River Basin. EMIT systems are capable 

of treating 336,000 to 1,176,000 gpd (8,000 to 28,000 bpd). 

Feed water quality bins The reported optimal feed water quality for the process is a NaHCO3

dominated feed with 3,500 mg/L TDS. 

Product water quality Treatment process permeate quality is dependent on feed water salinity 

and operating conditions. >97% rejection of Na is achievable, with 

additional removal of Mg, Ba, and HCO3. 

Production efficiency 

(recovery) 

Product water recovery is dependent on IX resin regeneration needs, 

but recovery typically exceeds 99%. 
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Table 40. Summary of technical assessment of EMIT Higgins Loop IX process.

Criteria Description/Rationale 

Infrastructure considerations This treatment process has operational footprint that varies from 220 

ft2 to 450 ft2

. 

System is reported to be skid based, and highly mobile. 

Energy consumption Energy requirements are estimated at 4.96 to 12.4 kWh/kgal(0.21 to 

0.52 kWh/bbl). 

Chemicals Chemical cleaning rates depend on feed water quality and IX resin 

adsorptive capacity. Resin regeneration will typically occur after 

certain product water quality specifications are exceeded. The 

regenerant solution is composed of 4.11 M HCl. Additional chemical 

disinfection may be required to mitigate biofouling and will typically 

consist of H2O2 or NaOCl cleaning solutions. 

Life cycle Strong acid cation exchange resins may perform for 10 to 15 years 

[114]. 

O&M considerations Monitoring and control required for flow rates, product water quality 

and resin regeneration. 

System will likely require minimal supervisory oversight. 

Level of flexibility: Low flexibility for treating feed water with 

alternative dominant feed solute or high organic loading. 

Level of robustness: IX processes are highly sensitive to fouling from 

organic materials and suspended solids. Care should be exercised to 

limit exposure of IX resin to oxidized metals and sparingly soluble 

mineral salts. Acid cation resins should not be exposed to feed 

temperatures in excess of 120 °C. 

Level of reliability: The Higgins Loop operates with an automated, 

short duration resin pulsing cycle to maintain IX resin productivity. 

Types of energy required: electrical. 

Overall costs Capital costs are unknown. Operations cost are most influenced by the 

market cost of HCl acid. 

Pre-and post treatment Process will require pretreatment options including suspended solids, 

oxidized metals, and scaling mineral removal. 

Product water may require pH stabilization or remineralization. This 

may be achieved by lime bed contacting or by blending small amounts 

of filtered and sterilized feedwater with product water. 

The concentrated feed stream may require additional post treatment or 

disposal consideration. Current practice is disposal by Class I or II 

injection wells. 

Concentrate management or 

waste disposal 

The spent resin regeneration solution will require neutralization. 

Relatively high recovery rates exceeding 99% generate very minor 

amounts of concentrated brine. 

Applicability for produced 

water treatment 

Excellent – Treatment well suited for specific feed water constituents 

(primarily NaHCO3), and widely utilized in the Powder River Basin. 

Process requires substantial chemical input in the form of IX resin 

regenerant, and is best suited for centralized treatment in areas with 

good transportation infrastructure. 

Note: 1 barrel = 42 US gallons 

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Drake: continuous selective IX process 

Drake Water Technologies, LLC is a Montana based company that has developed a 

patented IX process with minimal waste production [146]. The Drake system is designed to 

perform targeted removal of monovalent cations, especially sodium for SAR reduction, and is 

designed as a three-phase, continuous fluidized bed system. Though it is not recorded explicitly, 

it is likely that the Drake system utilizes a strong acid cation exchange resin. A system schematic 

is shown in Figure 40. System design includes a continuous circuit for dosing (22), loading (42 – 

fluidized bed rector), separating (16), and regenerating (14) the ion exchange media. The 

system’s primary patent claim is that it moderates resin and feed solution contact time by rotary 

valves (18 and 20) to reduce exchange of divalent ions. 

Figure 40. Drake: continuous selective IX process. Schematic taken from US patent [146]. 

 

The Drake system is in its third stage of pilot testing at a Willow Creek installation near 

Gillette, Wyoming in the Powder River Basin [147]. The third-generation Drake IX system is 

designed to treat 361,000 gpd (8,600 bpd) [144]. Pilot testing was conducted on a feed water 

with approximately 1,000 mg/L TDS; however, the process may be capable of treating water 

with marginally higher salinity. Recent pilot testing results indicate a sodium removal of 93%. 

System recovery is reported to be greater than 97% [147]. System reject is composed of highly 

concentrated Na2SO4, which may be dried and further concentrated in evaporation ponds to 

produce a commercial grade Na2SO4. 

 A Drake IX system is estimated to require two acres of surface area, which includes a one 

acre Na2SO4 collection impoundment [144]. The system may be deployed as small, modular shed 

that is capable of being towed on a trailer. In addition to a standard IX system, this process also 
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requires two 16,800 gal (400 bbl) water tanks and a 4,400 gal (105 bbl) H2SO4 regenerant tank 

[147]. Pre-treatment technologies may be required to remove resin foulants from the raw water 

supply. Energy requirements are not explicitly stated, but are likely to be slightly less than that 

required for the EMIT Higgins Loop system. Additional operation and management 

considerations may be inferred from the overall operation of IX processes. A technical 

assessment for the Drake IX process is summarized in Table 41. 

Table 41. Summary of technical assessment of the Drake IX process.

Criteria Description/Rationale 

Industrial status Pilot scale operations for CBM produced water treatment in the 

Powder River Basin. The current Drake system is designed to treat 

361,000 gpd (8,600 bpd). 

Feed water quality bins The system has been tested with 1,000 mg/L TDS feed water 

dominated by NaHCO3. 

Product water quality Treatment process permeate quality is dependent on feed water salinity 

and operating conditions. 93% rejection of Na ions is reported. 

Production efficiency 

(recovery) 

Product water recovery is dependent on feed water quality and IX resin 

regeneration needs, but recovery with ideal feed water is reported as 

97%. 

Infrastructure considerations This treatment process is reported to require a surface area of 

approximately 2 acres (87,000 ft2

). 

Individual systems may be highly mobile, however further 

construction may be necessary to provide increased protection from 

the elements. 

Energy consumption Energy requirements are minimal for most IX processes. No values are 

reported for the Drake system, but they may be inferred to be less than 

that required by the Higgins Loop. 

Chemicals Chemical cleaning rates depend on feed water quality and IX resin 

adsorptive capacity. H2SO4 regenerant is required to restore the IX 

resin’s adsorptive capacity. Additional chemical disinfection may be 

required to mitigate biofouling and will typically consist of H2O2 or 

NaOCl cleaning solutions. 

Life cycle Cation exchange resins may perform for 10 to 15 years [114]. 

O&M considerations Monitoring and control required for flow rates, product water quality 

and resin regeneration. 

System will likely require minimal supervisory oversight. 

Level of flexibility: System is optimized to remove Na ions, but will 

achieve moderate removal of divalent cations and metals. 

Level of robustness: IX processes are highly sensitive to fouling from 

organic materials and suspended solids. Care should be exercised to 

limit exposure of IX resin to oxidized metals and sparingly soluble 

mineral salts. Acid cation resins should not be exposed to feed 

temperatures in excess of 120 °C. 

Level of reliability: No information is provided on system up time. 

Types of energy required: electrical. 

Overall costs No data provided. 
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Table 41. Summary of technical assessment of the Drake IX process.

Criteria Description/Rationale 

Pre-and post treatment Process will require pretreatment options including suspended solids, 

oxidized metals, and scaling mineral removal. 

Product water is not likely to require remineralization. It may be 

necessary to blend small amounts of filtered and sterilized feedwater 

with product water. 

Concentrate management or 

waste disposal 

Relatively high recovery rates exceeding 97% generate very minor 

amounts of concentrated brine. The concentrated Na2SO4 regenerant 

stream may be further concentrated to produce a commercial grade 

salt. 

Applicability for produced 

water treatment 

Excellent – Treatment well suited for specific applications, specifically 

feed water dominated by NaHCO3. Process may require substantial 

chemical input in the form of IX resin regenerant, and may be best 

suited for centralized treatment in areas with good transportation 

infrastructure.

Note: 1 barrel = 42 US gallons 

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Eco-Tec: Recoflo® compressed-bed IX process 

A Canadian based company, Eco-Tec Inc. has developed two compressed bed IX systems 

that offer lower operational footprint, faster regeneration, and increased throughput compared to 

conventional IX processes. The compressed bed systems are an extension of conventional 

packed bed IX processes. The Eco-Tec systems are differentiated by one system that has two 

separate compressed-bed columns for anion and cation removal, and a second system with three 

separate compressed-bed columns that contain a primary cation bed and anion bed followed by a 

polishing cation bed. The ion exchange resin employed by the Recoflo® process is composed of 

fine mesh resins that are reported to increase exchange kinetics [148, 149]. A photograph of the 

two-bed system is shown in Figure 41. 

Figure 41. Eco-Tec Recoflo® compressed bed IX system. Of the two cylindrical beds pictured, 

one is loaded with cation exchange resin and the other with anion exchange resin. Each column 

houses 3 to 6 inches of ion exchange resin [148]. 

Eco-Tec Recoflo® systems have been employed to treat copper electrolyte solutions, 

recover nickel salts, recover metals from process solutions, and purify alternative fuels [150]. 

Recently, Eco-Tec was awarded a service contract for a Marathon installation in the Powder 

River Basin (WY) [151]. The system is designed to treat 1.5 MGD (36,000 bpd) produced water. 

The Recoflo® system is designed to operate with a short duration run time of 30 minutes 

followed by a seven minute regeneration period. Eco-Tec claims that operating the system in this 

manner increases the access to most exchange sites on the resin, which increases exchange rates 

for both the IX and regeneration process [149]. The system requires both H2SO4 and NaOH to 

regenerate the cation and anion IX resins, respectively. Recoflo® compressed beds are more 

mobile than conventional IX processes and the Higgins Loop. A schematic of a full treatment 

train with two, skid-mounted three-bed systems operating in parallel is shown in Figure 42. A 

summary of the technical assessment for the Eco-Tec Recoflo® compressed-bed IX process is 

shown in Table 42. 
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Figure 42. System schematic with two three-bed Eco-Tec Recoflo® process operating in parallel. 

Note that pretreatment is required to remove resin foulants from the feed stream [148]. 

Table 42. Summary of technical assessment of the Eco-Tec Recoflo® compressed-bed IX 

process.

Criteria Description/Rationale 

Industrial status Pilot scale operations for CBM produced water treatment in the 

Powder River Basin. The current Eco-Tec system is designed to treat 

1.5 Mgd (36,000 bpd). 

Feed water quality bins Current installations of the Eco-Tec system have been in the 

microelectronics industry. The system is utilized primarily as a 

polishing step for water that is already of high purity. No data is 

currently available on the CBM produced water that the system is 

operating with in the PRB. 

Product water quality Treatment process permeate quality is dependent on feed water salinity 

and operating conditions. >90% rejection of Na, Mg, Ca, and SO4 ions 

is expected, in addition to significant metals removal. 

Production efficiency 

(recovery) 

No data is provided regarding overall process production efficiency. 

Infrastructure considerations Eco-Tec’s Recoflo® system is designed to utilize a smaller operational 

footprint that conventional IX processes, however no data is available 

to specify the exact footprint of the system. 

Individual systems may be highly mobile; however, further 

construction may be necessary to provide increased protection from 

the elements. 

Energy consumption Energy requirements are minimal for most IX processes. No values are 

reported for the Eco-Tec system, but they may be inferred to be less 

than that required by the Higgins Loop. 
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Table 42. Summary of technical assessment of the Eco-Tec Recoflo® compressed-bed IX 

process.

Criteria Description/Rationale 

Chemicals Chemical cleaning rates depend on feed water quality and IX resin 

adsorptive capacity. H2SO4 and NaOH regenerant solutions are 

required to restore the IX resin’s adsorptive capacity. Additional 

chemical disinfection may be required to mitigate biofouling and will 

typically consist of H2O2 or NaOCl cleaning solutions. 

Life cycle Cation exchange resins may perform for 10 to 15 years, while anion 

exchange resins may last for only 4 to 8 years [114].

O&M considerations Monitoring and control required for flow rates, product water quality 

and resin regeneration. 

System will likely require minimal supervisory oversight. 

Level of flexibility: Specifics on the treatment process’ capabilities is 

unknown, however the system may require considerable IX resin 

regeneration for feed water with higher TDS. 

Level of robustness: IX processes are highly sensitive to fouling from 

organic materials and suspended solids. Care should be exercised to 

limit exposure of IX resin to oxidized metals and sparingly soluble 

mineral salts. 

Level of reliability: System is marketed with the stipulation of 30 

minute on-stream followed by 7 minutes of regeneration. 

Types of energy required: electrical. 

Overall costs No data provided. 

Pre-and post treatment Process will require pretreatment options including suspended solids, 

oxidized metals, and scaling mineral removal. 

Product water is may require remineralization. It may be necessary to 

blend small amounts of filtered and sterilized feedwater with product 

water. 

Concentrate management or 

waste disposal 

IX processes tend to have high recovery, however the Eco-Tec system 

may have lower recovery due to its IX resin regeneration needs. 

Applicability for produced 

water treatment 

Excellent – Treatment well suited for specific applications, may 

provide exceptional post-treatment capabilities for selective ion 

removal (e.g., boron or radionuclides).

Note: 1 barrel = 42 US gallons 

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Catalyx Fluid Solutions/RGBL IX Process 

RGBL acquired the rights to an IX process developed by Catalyx Fluid Solutions. The 

Catalyx system is a patented IX process that was designed to minimize waste during resin 

regeneration (wasting only 25-50% for each regeneration cycle) and rinse water according to 

manufacturer information [152]. The Catalyx system was designed for the removal of sodium 

(by ion exchange) and bicarbonate (through off gassing of CO2), with the ion exchange chemical 

reaction: 

Na  HCO3

  R

H   RNa   H2O  CO2 

Waste minimization is facilitated by the use of three tanks that are responsible for 

shuffling regenerant and rinse waters of various qualities during IX resin regeneration cycles. 

During the onset of a regeneration cycle, acidic regenerant utilized from the previous 

regeneration cycle is first processed through the packed bed of resin in a counter-current 

direction and wasted. A second tank containing acidified rinse water from the previous 

regeneration cycle is then processed through the packed bed and recollected in the first tank. The 

third tank contains rinse (product) water, which is employed to flush any remaining regenerate 

out of the packed bed. Once the rinse water is processed through the IX bed it is collected in the 

second tank. The third tank is refilled with product water during normal operation of the system 

[152]. 

Only trivial technical literature, and no field piloting results are available to discuss the 

broader merits and limitations of this technology. 

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Commercial Membrane Processes 

CDM Produced Water Technology 

CDM has developed a process for treating produced water containing TDS levels up to 

20,000 mg/L. The technology is not specific for coal bed methane (CBM) produced water and 

has been pilot tested with tight sands produced water in the Piceance Basin and with CBM 

produced water in the Powder Rive Basin. CDM is also marketing the technology for treating 

flow-back water from subsurface hydraulic fracturing. 

The treatment process is comprised of a train of different technologies in series to meet 

site-specific treatment goals (Figure 43). The specific processes included in the treatment train 

are dictated by the feed water quality and the desired product water quality. Some of the 

technologies that may be utilized include: advanced filtration, weak acid cation IX softener, UV

disinfection, low pressure RO, antiscalant addition, seawater/high pressure RO, evaporation, and 

crystallization. The feed stream is kept anoxic to minimize oxidation of iron and other metals, 

and to reduce the fouling potential of the water. Depending on the feed water quality, the process 

can achieve more than 97% recovery. A computer program was developed that assists in 

selecting the required technologies and predicts the performance and scale formation within the 

system based on feed water quality. 

The pretreatment for the process consists of media filers, and polymeric hollow fiber UF

membranes to remove particulates, silt, oil, grease, coal fines, clay, and bacteria. The filtration 

system is backwashed using RO permeate. A weak acid cation (WAC) IX softener is used to 

reduce hardness and other metals. The resin is regenerated using hydrochloric acid. The water is 

then disinfected using UV. The calcium and magnesium-rich WAC regeneration solution is 

combined with the filter backwash and is either treated separately or combined with the product 

streams from the membrane processes and discharged, depending on the scenario and the feed 

water quality. 

After pretreatment, low-pressure reverse osmosis (capable of achieving 85% recovery) is 

employed. The train size and type of membrane employed is tailored based on the feed water 

quality. An antiscalant (~10 mg/L) is added to the concentrate stream to stabilize the silica and to 

prevent scale formation in the next high-pressure RO stage. The second RO stage consists of 

high-pressure or seawater RO membranes that can achieve 80% water recovery. The RO 

permeate is combined with the low-pressure RO permeate for discharge or beneficial use. The 

concentrate, approximately 2 to 3% of the initial feed volume, is either disposed of as a waste, or 

can be treated for ZLD. 

Because many produced waters contain high levels of sodium and low levels of divalent 

ions, the sodium adsorption ratio (SAR) may be too high even after treatment for the water to be 

put to beneficial use. In these cases, a limestone bed is used to add calcium to the water and 

lower the SAR. 

Some produced water applications may require ZLD because brine disposal is not 

feasible or is too expensive. For ZLD applications, the concentrate from the second stage RO is 

fed to an evaporator. Evaporators are very energy intensive and therefore the energy for the 

evaporator can be obtained from natural gas waste heat from a compressor at the well field. The 

distillate from the evaporator is combined with the RO permeate streams for discharge or for 

other beneficial uses. The residuals from the evaporator can be either concentrated brine or 

solids. Depending on feed water quality and discharge permits, filter backwash stream and WAC 
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regeneration brine can be blended with the product water streams (low and high pressure RO and 

evaporation) before discharge. 

The CDM process has been pilot tested with CBM produced water feed from the Powder 

River Basin and with tight sands gas produced water from the Piceance Basin. The CBM 

produced water contained emulsified oil and grease, particulates, and silt. Sodium bicarbonate 

was the dominant salt. The tight sands gas produced water contained 438 mg/L oil and grease, 

and 119 mg/L silica. No operational data was available for either test site. 

The following cost estimates were presented based on the pilot testing experience in the 

Powder River Basin: $0.14/bbl or $3.33/1000 gal (not including energy or brine disposal), 

$0.08/bbl or $1.90/1000 gal for brine disposal. Cost estimates were not provided for the pilot test 

on tight sands produced water. 

The following water quality issues affecting pretreatment were identified: silt, suspended 

solids, oil coated particles, and coal fines. Water quality issues affecting the RO processes 

include: calcium harness, iron, barium, silica, and microbial fouling. CDM found that for CBM 

produced water, sodium bicarbonate solubility is the limiting factor for further increasing the 

system recovery. In order to accommodate changing water volumes, modular systems can be 

designed to treat volumes from 5,000 bbl/day (200,000 gpd or 145.8 gpm) to 20,000 bbl/day 

(840,000 gpd or 583 gpm) with additional units added or removed, as necessary. A technical 

assessment of the CDM process is summarized in Table 43. 

Figure 43. CDM produced water treatment technology: process diagram. 

(http://ipec.utulsa.edu/Conf2008/Manuscripts%20&%20presentations%20received/Kimball_24.pdf). 
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Table 43. CDM Process Assessment. 

Criteria Description/Rationale 

Status of technology This process has been tested on a coal bed methane application in the 

Powder River Basin. It has also been tested on a tight sands water 

applications in the Piceance Basin. No commercial installations exist at 

the time of publication of this document. 

Feed water quality bins ≤ 40,000 mg/L TDS. 

Product water quality The system can be tailored by adding and removing unit processes to 

meet different product water criteria. 

Recovery Depends on feed water quality and unit processes used. Water 

recovery may range from 50% to greater than 90%. 

Energy use Highly dependent on the number and type of unit processes used. No 

information available. 

Chemicals use Highly dependent on the number and type of unit processes used. No 

information available. 

Expected lifetime of critical 

components 

Membrane replacement will be necessary every 5 to 10 years 

depending on the applications. Other system components will have a 

life expectancy of 10 to 20 years. 

Infrastructure considerations The CDM process comes as a package solution. Site preparation is 

required. 

O&M considerations This process will most likely require large amounts of energy and 

chemicals. 

Capital and O&M costs None available. Contact manufacturer. 

Pretreatment of feed water The CDM process is designed to be a standalone technology that 

includes all necessary pretreatment technologies. 

Post treatment of product water The CDM process is designed to be a standalone technology that 

includes all necessary post treatment technologies. 

Concentrate management or 

waste disposal 

See fact sheets for individual processes. Waste depends on specific 

system components used. 

Note: 1 barrel = 42 US gallons 

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Veolia Water Solutions and Technologies: OPUSTM – optimized pretreatment and separation 

technology 

 N.A. Water Systems, a Veolia Water Solutions and Technology company, designed the 

OPUSTM system. OPUSTM is a proprietary optimized pretreatment and unique separation process 

for desalination of water with high concentrations of sparingly soluble solutes (e.g., SiO2, 

CaSO4, and Mg(OH)2), organics, and boron. The system is able to achieve high recovery with 

high purity product water through the use of extensive pretreatment processes prior to water 

contacting both IX and RO sub-systems. A system schematic is shown in Figure 44. 

Figure 44. Process schematic of Veolia Water Solutions and Technologies: OPUSTM CBM 

produced water treatment system (Source: [153]). 

The process first performs acidification and degasification of the raw feed water. This is 

followed by an aggressive, conventional coagulation, flocculation, and high-rate plate settler 

sedimentation process, which is termed MultifloTM chemical softening in the OPUSTM literature 

[153]. After this step, the feed stream should be devoid of nearly all high-molecular-weight 

organic molecules and oxidized metals (particularly iron and manganese). Additionally, colloidal 

silica is partially removed by co-precipitation. Decant from the sedimentation basin is then 

filtered by a packed-bed media filtration column, which removes any microflocs and most 

suspended solids that did not settle out in the plate settlers. The media filter may also achieve 

additional removal of low to medium molecular weight hydrophobic organic molecules, 

including any remaining oil and grease. 

Filtrate from the media filter is then processed through a mixed, packed-bed IX column 

for further water softening and removal of microorganisms. A cartridge filter is then employed to 

remove any IX resin or any remaining suspended solids prior to contact with the RO membranes. 

The water is then pressurized and treated by BWRO membranes at an elevated pH. Operating the 

RO elements under this condition reduces the fouling propensity of silica and increases the 

rejection of both silica and boron. 

In April of 2008 the OPUSTM system was field tested at a steam-enhanced oil production 

site in San Ardo, CA. The tested OPUSTM system was designed to treat 2.1 MGD (50,000 bpd) 

of water with high boron, silica, and organics concentrations [154]. Water recovery for the 

OPUSTM is described by the manufacturer as high, and may be equivalent to that of other high 

recovery RO systems that operate with elevated pH. OPUSTM product literature indicates 

removals for TDS of 99.6%, TOC of 99%, silica of 99.9%, and boron of 99.4% [154]. Sodium 

removal is not indicated, however it may be considered similar to that for BWRO processes. 
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The product literature makes little mention of system mobility; however, it is possible 

that the entire system could fit in several cargo trailers. No data is provided on the system 

footprint or energy consumption. The MutlifloTM pretreatment component requires significant 

chemical input in the form of acids (possibly HCl or H2SO4), coagulants (potential chemicals 

include Fe2(SO4)3 and Alum), alkali compounds (likely Ca(OH)2), and polymer aids (candidates 

include polyDADMAC or PAC) [110]. Additional chemical demand is created by the IX 

regenerant solution that may require both acid and base regenerants, as well as base chemicals 

required to increase the pH of the RO feed water. 

OPUSTM literature does not present a life cycle assessment of the system; however, 

BWRO membranes are known to have a 3 to 7 year lifespan and IX resin typically requires 

replacement after 5 to 10 years [36, 114]. The OPUSTM system likely requires substantial process 

automation and control. Moderate operator oversight may be required, especially for 

management of the MultifloTM pretreatment system. 

OPUSTM represents a highly flexible and robust treatment process and can operate with 

highly variable feed water quality. With proper management the system likely requires minimal 

down time and maintenance. Cost figures related to capital, and operating costs are not reported. 

The system generates concentrated brine and IX regenerant that require disposal and may require 

chemical stabilization. Sludge is generated during the pretreatment process and requires disposal 

in landfills. A technical assessment of the Veolia Water Solutions and Technologies: OPUSTM – 

optimized pretreatment and separation technology is summarized in Table 44. 

Table 44. Summary of technical assessment for Veolia Water Solutions and Technologies: 

OPUSTM – optimized pretreatment and separation technology.

Criteria Description/Rationale 

Industrial status System has undergone field trials at a steam-enhanced oil production field 

in San Ardo, CA. 

Feed water quality bins The estimated TDS application range is between 500 mg/L and 10,000 

mg/L. High removals of monovalent and divalent ions, metals, and 

organics is expected. System is likely to achieve additional silica and 

boron removal with high pH operation. 

Product water quality Treatment process permeate quality is dependent on feed water salinity and 

operating conditions. Product literature reports >99% rejection of TDS and 

most multivalent solutes. System is likely to achieve >94% removal of Na 

based on typical BWRO performance. 

Production efficiency 

(recovery) 

Product water recovery is estimated to exceed 90%. 

Infrastructure 

considerations 

This treatment process will require a substantially larger footprint that 

conventional RO or IX systems. Substantial chemical storage and sludge 

dewatering facilities will be required. 

System mobility is reduced compared to conventional RO systems. 

MutlifloTM pretreatment process along with chemical storage components 

is the primary factors in limiting mobility. 

Energy consumption Energy requirements are unknown. 
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Table 44. Summary of technical assessment for Veolia Water Solutions and Technologies: 

OPUSTM – optimized pretreatment and separation technology.

Criteria Description/Rationale 

Chemicals MultifloTM pretreatment system will require multiple chemical compounds 

to operate and include acids, bases, hydrolyzing metal coagulants, and 

polymer based coagulants. Examples of these chemicals are provided in 

the main body of this report. 

Chemical cleaning rates depend on feed water quality. Cleaning will 

typically occur after certain design specifications are exceeded, and may 

require the use of NaOH, Na4EDTA, or HCl. IX process will require 

regeneration with strong acid, likely H2SO4 or HCl. 

Life cycle No data is currently available. 

O&M considerations Substantial monitoring and control required for flow rates, chemical 

dosing, IX regeneration, and RO element pressure. 

System may require moderate oversight to ensure proper operation of the 

primary RO stage brine management systems. 

Level of flexibility: Highly flexible system that may readily adapt to 

changes in feed water quality. 

Level of robustness: TFC membranes have high pH tolerance, but cannot 

be exposed to feed temperatures in excess of 113 °F (45 °C). 

Level of reliability: RO and IX systems operate semi-continuously with 

automated, short duration chemical rinses or osmotic backwashing cycles 

(for RO). 

Types of energy required: electrical. 

Overall costs Capital costs are unknown. 

Pre-and post treatment Product water will require pH stabilization or remineralization. This may 

be achieved by lime bed contacting or by blending small amounts of 

filtered and sterilized feed water with permeate. 

Concentrate management or 

waste disposal 

No special concentrate treatment is required. Relatively high recovery rates 

exceeding 90% generate very minor amounts of concentrated brine. 

Sludge from the sedimentation basin will require dewatering and landfill 

application. 

Applicability for produced 

water treatment 

Excellent – Treatment provides robust pretreatment to limit foulant loading 

on high-pressure membranes.

Note: 1 barrel = 42 US gallons 

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New Logic Research: VSEP® - Vibratory Shear Enhanced Membrane Filtration 

The patented VSEP® technique was developed by New Logic International in 

California. The VSEP® membrane filter pack consists of leaf elements arrayed as parallel discs 

and separated by gaskets. The shear waves produced by the membrane vibration cause solids and 

foulants to be lifted off the membrane surface and remixed with the bulk material flowing 

through the membrane stack (Figure 45). This high shear processing exposes the membrane 

pores for maximum throughput that is typically between 3 and 10 times the throughput of 

conventional cross-flow systems [155]. Compared to conventional RO systems, VSEP® is not 

limited by the solubility of minerals or the presence of suspended solids. It can be used in the 

same applications as crystallizers or brine concentrators and is capable of high water recoveries 

of up to 90% [156]. The VSEP® system can be configured to employ either RO or NF

membranes in a single-stage or multiple-stage arrangement. The configuration depends on feed 

water quality, water quality goals of the VSEP® permeate, and targeted water recovery. 

Figure 45. Fouling reduction mechanisms of VSEP® (Source: [155]). 

The manufacturer claims that the VSEP® process has several advantages over 

conventional membrane process [157]. These include: 

 Minimal pretreatment: Because of high shearing energy at the membrane surface and 

near the pores, colloidal fouling and concentration polarization are greatly reduced. 

The use of pretreatment to prevent scale formation is not required. 

 Low fouling and scaling potential: Sinusoidal shear waves from the membrane 

surface help to repel approaching particles and colloids; thus, reduce fouling and 

scaling potential. 

 High permeate flux: The throughput rates of VSEP® are 5-15 times higher. The 

sinusoidal shear waves propagating from the membrane surface act to hold suspended 

particles above the membrane surface allowing free transport of the liquid through the 

membrane. 
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 Low energy consumption: High flux, and minimized membrane scaling and fouling 

make VSEP® very energy efficient (0.27 kWh/kgal filtrate). 

 Small footprint: The VSEP® membrane system has a vertical plate-and-frame 

configuration, where hundreds of membrane leafs are stacked on top of each other. 

This results in a very small horizontal footprint of the unit. As much as 2000 square 

feet (185 m2

) of membrane is contained in one VSEP® module with a footprint of 

4x4 ft. 

The combined advantages make VSEP® an attractive technology for treatment of 

produced water. New Logic has been testing VSEP® for produced water treatment - both 

onshore and offshore. Test were conducted in California, the North Sea, Latin America, and 

Alberta's Oil Sands [158]. Several produced water projects are listed in Table 45. 

Table 45. VSEP® produced water projects.

Produced water type Location MGD bbl/day 

CBM Produced Water Utah 0.72 17143 

Offshore Produced Water Santa Maria, CA 0.86 20571 

Oil Produced Water Santa Maria, CA 0.22 5143 

Oil Produced Water Bakersfield, CA 12.24 291429 

Produced Water Kuwait 1.44 34286 

Offshore Produced Water Peru 0.05 1200 

Note: 1 barrel = 42 US gallons 

In 2006, the first full-scale VSEP® system was selected to create steam quality water 

from oilfield produced brine at a BreitBurn Energy facility in Santa Barbara, California. 

BreitBurn implements steam flooding in the process and is using steam generators in the 

operations to enhance oil production. Re-injection of produced water into the source formations 

was the method of disposal. After on-site trials, BreitBurn determined that the VSEP® system 

provided a cost-effective solution capable of removing the contaminants and providing the 

needed boiler feed water; thus, eliminating the need for expensive pretreatment and chemical 

usage. 

The BreitBurn produced water is high in alkalinity, silica, sodium, carbonate, and TOC. 

The feed to the VSEP® contains 25,900 mg/L TDS and 870 mg/L hardness. The TOC was 

mostly made up of paraffins, waxes, and asphaltenes that are colloidal materials that do not 

readily separate using conventional methods. Asphaltenes tend to adsorb at water-in-crude oil 

interfaced to form a rigid film surrounding the interface. A schematic drawing of the BreitBurn 

treatment process is shown in Figure 46. The treatment employs both NF and RO membranes. 

The final permeate, after two stages of filtration, has a non-detectable concentrations of hardness 

and water quality that is suitable for boiler feed water. The VSEP® process achieved an overall 

recovery of 70% of the oil produced water as clean boiler feed water. 
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Figure 46. Schematic of the BreitBurn treatment process of oil produced water. 

The VSEP® process has proven effective in treating high solids water. The VSEP®

may not be economical for CBM produced water that has less solids and can be treated by 

conventional membrane processes. A technical assessment of the VSEP® treatment process is 

summarized in Table 46. Data is based on the information provided on the website of the 

manufacturer. 
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Table 46. Summary of technical assessment of VSEP® process. 

Criteria Description/Rationale 

Industrial status Full-scale application for produced water treatment (offshore and onshore) 

Feed water quality bins Applicable to TDS <30,000 mg/L, and a broad variety of water chemistry 

makeup. 

Product water quality Similar to other membrane technology, product water quality depends on the 

molecular cut-off of the membrane. High water quality can be expected by 

using RO membranes. 

Production efficiency 

(recovery) 

Product water recovery is between 70 and 90%, depending on feed water 

quality. 

Infrastructure 

considerations 

Require up to 17’ in ceiling clearance. The VSEP® units are vertical and 

compact. The footprint of a 2000 SF of membrane unit is 4’x4’, and can be 

installed into a container with a volume of about 15 Cubic Feet. Require gas or 

electricity as power. 

Energy consumption The energy consumption is low, and reported 0.27 kWh/kgal of product water 

[157]. 

Chemicals No chemical requirement for pretreatment. Chemicals are required for 

membrane cleaning. 

Life cycle As an emerging technology, no life cycle is reported. Due to high sheer force, 

shorter membrane lifetime may be expected as compared to conventional 

membranes. 

O&M considerations High level of monitoring and control required. 

High level of skilled labor required to operate VSEP®

 process. 

High level of flexibility: easy to adapt to highly varying water quality and 

quantity. 

The level of robustness and reliability need to be demonstrated through longterm operation. 

Types of energy required: electricity. 

Overall costs The capital and construction costs of VSEP® are site specific. For produced 

water/bilge water treatment, the VSEP® system power consumption is 

estimated $0.31/kgal (based on 0.05 $/kWh electricity cost); the system 

maintenance & cleaning is about $0.37/kgal [157]. 

Pre-and post treatment No or minimal pre-treatment such as settling, prescreen, or cartridge filtration 

to remove suspended solids and organic matter. 

Depending on product water quality, remineralization or blending may be 

required. 

Concentrate 

management or waste 

disposal 

The brine stream needs transported off the well site and disposal. 

Applicability in 

produced water 

treatment 

Excellent technology for the produced water application, may not be 

economical for CBM water application due to high energy consumption and 

less solids in water. 

Note: 1 barrel = 42 US gallons 

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Eco-Sphere: OzonixTM 

Eco-Sphere has developed a semi-truck trailer-mounted, advanced oxidation system that 

is primarily marketed for the treatment and reuse of frac flow-back water, but may have merit for 

oil and gas produced water treatment. The packaged system first employs settling tanks and a 

large mesh particle filter to screen out particles and large suspended solids, respectively. 

Decanted feed water is then pumped into a reaction vessel and is flash mixed with supersaturated 

ozonated water. The ozone is decomposed into hydroxyl radicals by ultrasonic transducers, 

which readily oxidizes metals, decomposes soluble and insoluble organic compounds and 

microorganisms. Ultrasonic transducers also induce cavitations among the dissolved ozone 

bubbles, which act to induce shearing of larger particles and decreases particle flotation times. 

The reaction vessel also employs two electrodes to facilitate precipitation of hard salts from the 

influent. Aluminum sulfate is then dosed into the solution to facilitate particle coagulation. The 

ozonated, coagulated water is then passed through a centrifuge to remove all oxidized material. 

Activated carbon cartridge filter are then utilized to remove any remaining organic compounds 

or suspended solids from the solution. RO membranes are employed as a final step to remove 

monovalent and divalent inorganic solutes [159, 160]. 

A proof-of-concept pilot study was conducted with the OzonixTM system in the Woodford 

Shale Play in November of 2008 [160]. Newfield Exploration Mid-Continent, Inc. tested the 

process on frac flowback water from a field near Coalgate, OK. The frac flowback water was 

characterized as having an influent TDS of 14,000 mg/L (dominated by chloride, sodium, and 

potassium), TSS constituting of 65 mg/L, TOC of 65 mg/L, total oil and grease of 14 mg/L, 

barium concentration of 35 mg/L, total BTEX of 38 μg/L, and radionuclide counts (reported as 

gross alpha) of 264 pCi/L. The system was housed in a large mobile trailer and was used to treat 

100 bph (4,200 gph) of frac flowback water for 12-14 hours per day for two weeks. A third party 

consultant group was hired to provide quality assurance and quality control for the study. A 220 

kW electrical energy generator was utilized to power the system during field trials. Assuming a 

13-hour workday, this equates to 2,860 kWh of energy consumed to treat 1,300 bbl (54.6 kgal) of 

water. Based on these calculations, the specific energy consumption per bbl of water treated is 

2.2 kWh/bbl (52 kWh/kgal). The manufacturer claims that purified water recovery may exceed 

75%, and only 1% of the initial bulk volume needing disposal. The resulting waste stream is 

likely disposed of in class I or II injection wells. No mention is made of solids disposal issues 

related to the initial solids separation and centrifuge processes. Chemical requirements are 

reported to include aluminum sulfate and antiscalant. The pilot system required three people to 

operate; however, the manufacturer estimates that only two operators would be required with 

further process automation. A technical assessment of the Ozonix treatment process is 

summarized in Table 47. 

Table 47. Summary of technical assessment for Eco-Sphere: OzonixTM process. 

Criteria Description/Rationale 

Industrial status Pilot scale study with frac water flowback in the Woodford Shale Play of 

eastern Oklahoma. System piloted for 2 weeks and treated 4,200 gph (100 

pbd). 

Feed water quality bins System was tested with highly challenging feed water. TDS of 14,000 mg/L, 

presence of dispersed oils, over 1,000 mg/L of total hardness, and presence of 

barium. 

Product water quality Pilot study reports 99.1% TDS rejection, and 97% removal of BTEX 

compounds. 
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Table 47. Summary of technical assessment for Eco-Sphere: OzonixTM process. 

Criteria Description/Rationale 

Production efficiency 

(recovery) 

Pilot study reports purified water recovery approaching 75%. Vendor claims a 

1% waste stream for disposal, with the rest of the solution being retained for 

reuse as frac water. 

Infrastructure 

considerations 

Operational footprint of pilot study system is reported as being ‘roughly’ the 

size of a frac tank. 

Energy consumption The energy consumption is estimated at 52 kWh/kgal (2.2 kWh/bbl) 

Chemicals Chemical requirements include aluminum sulfate for coagulation and scale 

inhibitors for RO subsystem. 

Life cycle Life cycle information is not yet available. 

O&M considerations Commercial system is expected to require two-fulltime operators. 

High level of flexibility: easily adapts to highly varying water quality and 

quantity. 

Highly robust pretreatment process. 

Reliability needs to be demonstrated through long-term operation. 

Types of energy required: electrical. 

Overall costs Operational and capitol costs are not specified by vendor. 

Pre-and post treatment All pretreatment requirements are already integrated into the system. 

Remineralization and water stabilization may be required for RO permeate 

stream. 

Concentrate 

management or waste 

disposal 

Any remaining brine stream will require disposal through injection. 

Applicability for 

produced water 

treatment 

Excellent – Treatment provides robust pretreatment to limit organic and hard 

salt loading on high-pressure membranes. 

Note: 1 barrel = 42 US gallons 

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GeoPure Water Technologies, LLC 

The GeoPure desalination process is a combination of pre-treatment, UF, and RO. These 

three treatment steps are operated in series to treat a wide range of produced water compositions 

and produce clean water that may then be discharged or reused. This technology was specifically 

developed for the desalination of oil and gas produced waters. Pilot scale systems have been 

tested in Texas A&M laboratories and at 12 field locations throughout Texas. The manufacturer 

[161] claims to have purified produced waters containing up to 50,000 mg/L TDS, but does not 

cite any specific studies. Depending on raw water quality, this process employs various 

pretreatment processes to remove dispersed oil, suspended solids, or dissolved hydrocarbons. 

The pretreated water is then further purified with polymeric UF and RO. The UF system 

provides a final barrier to suspended solids (such as colloids) prior to the RO subsystem. 

 GeoPure Water Technologies, LLC performed a field test of its commercial desalination 

unit in the Barnett Shale Play of central Texas in 2006 [162, 163]. In this field trial, frac 

flowback water was treated at a feed rate of 210,000 gpd (5,000 bpd). The feed water from this 

field trial also contained 4,200 mg/L TSS, 170 mg/L Fe, and 940 mg/L Ba. After 

coagulation/flocculation, the water was treated with GeoPure’s UF and RO units. Influent and 

RO permeate TDS concentrations were 15,000 and 190 mg/L, respectively, corresponding to 

98.7% TDS rejection. When including the coagulation/flocculation pretreatment process, total 

treatment costs were estimated to average $0.94 per barrel. 

 A second field trial was conducted at a CBM well field in Western Wyoming [162, 164]. 

The GeoPure treatment process was tested with CBM produced water containing corrosion 

inhibitor, alcohols, and surfactants. Other feed water parameters include a feed TDS of 9,700 

mg/L (dominated by NaCl) and 41 mg/L of dissolved hydrocarbons. 99% rejection of TDS was 

achieved. No electrical or other cost information was provided from this study. 

 GeoPure focuses on optimizing pretreatment technologies to protect its core UF/RO 

treatment processes from membrane foulants (especially dispersed oils). A technical assessment 

of the GeoPure treatment process is summarized in Table 48. 

Table 48. Summary of technical assessment for GeoPure Water Technologies, LLC. 

Criteria Description/Rationale 

Industrial status Oil and natural gas related field trials have reportedly been conducted at 12 

sites. Two summary documents from field trial experiences with frac flowback 

water in Texas and CBM produced water in Wyoming were located. 

Feed water quality bins The vendor reports treating water in excess of 50,000 mg/L TDS. Available 

field trial reports report treating water with TDS ranging from 9,700 to 15,000 

mg/L. Frac flowback water constituted high concentrations of barium, 

dissolved hydrocarbons, and iron. 

Product water quality 98-99% rejection of TDS was reported in available field-testing reports. 

Production efficiency 

(recovery) 

Product water recovery in one field test was reported to be 50%. 60-70% 

recovery is estimated for feed water of 7,000 and 17,000 ppm chlorides, 

respectively. 
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Table 48. Summary of technical assessment for GeoPure Water Technologies, LLC. 

Criteria Description/Rationale 

Infrastructure 

considerations 

Depending on the type of pretreatment needed, foot print size will vary. The 

average footprint will be larger than typical RO system on account of 

pretreatment needs such as chemical storage and settling basin for 

coagulation/flocculation. 

System mobility is reduced compared to conventional RO systems. 

Coagulation/flocculation is a contributing factor to lack of mobility. 

Energy consumption Energy consumption was not report for this system. 

Chemicals Chemical such as Alum or FeCl3 or similar coagulants may be necessary for 

pretreatment. RO system may require scale inhibitor. Also, chemicals 

necessary for membrane cleaning would be similar to those reported previously 

for RO and UF. 

Life cycle No data is currently available 

O&M considerations System employs standard automation for RO and UF systems. 

System may require moderate oversight to ensure proper operation of the 

coagulation/flocculation sludge and RO brine management systems. 

Level of flexibility: Able to adapt to various feed water types on account of 

pretreatment options. 

Level of robustness: 60-day field test of semi-continuous operation showed no 

permanent fouling of the membranes. 

Level of reliability: UF and RO systems operate semi-continuously with 

automated, short duration chemical rinses or osmotic backwashing (for RO). 

Types of energy required: electrical. 

Overall costs Capital costs are unpublished, while operation and management costs for the 

Barnett Shale Trend study seen above were found to be $0.94/bbl. 

Pre-and post treatment pH adjustment and remineralization may be required. 

Concentrate 

management or waste 

disposal 

Concentrate treatment is required on account of relatively low recovery rate. 

Sludge from the sedimentation basin will require dewatering and landfill 

application. 

Applicability for 

produced water 

treatment 

Excellent – Multiple pretreatment options provide system with considerable 

flexibility.

Note: 1 barrel = 42 US gallons 

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Geo-Processors: Sal-ProcTM, ROSP, and SEPCON 

Sal-ProcTM, linked RO – Sal-Proc (ROSP), and Saline Effluent to Products Conversion 

(SEPCON) are all treatment technologies developed by Geo-Processors USA, Inc. The SalProcTM technology is at the heart of both ROSP and SEPCON systems, and is a patented 

technology. The process was designed to facilitate the sequential or selective precipitation and 

extraction of specific dissolved chemical compounds and salts from saline waters. Depending on 

the chemical composition of the saline feed stream, the process combines well established 

chemical reactions and process engineering with evapo-cooling and crystallization steps for 

selective salt recovery. A simplified flow diagram of this process is shown in Figure 47. 

Figure 47: Process flow of Sal-ProcTM system (Source: [165]). 

The final product of the Sal-ProcTM system is a refined chemical salt that may have 

commercial value; depending on feed water quality these salts may include CaSO4, Mg(OH)2, 

NaCl, CaCl2, NaOH, CaCO3, and Na2CO3 [166]. 

When the Sal-Proc technology is integrated with a RO treatment system, the combined 

system is termed ROSP. The combination of these processes enables the conversion of saline 

impaired water into fresh water and useful chemical compounds. ROSP systems may employ 

Sal-ProcTM as a pretreatment process for removal of sparingly soluble salts prior to contact with 

the RO membrane, or as post treatment to reduce brine disposal volume and cost [165]. 

Saline Effluent to Products Conversion (SEPCON) facilities are defined by GeoProcessors USA, Inc. as any installation that utilizes Sal-ProcTM, or by natural extension, ROSP 

subsystems as part of their brine management strategy. A SEPCON demonstration and testing 

facility is currently under construction in California (2009). SEPCON systems are expected to 

have reduced operating costs with increased feed water throughput [165]. The number of 

possible system configurations that could utilize a Sal-ProcTM subsystem is too numerous to list; 

therefore, the remainder of this technology’s technical summary focuses on the stand-alone SalProcTM process. 
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The Sal-ProcTM system has undergone a sustained period of development and 

improvements including field trials, piloting, and public demonstrations. Sal-ProcTM systems 

have been employed at various installations with treatment capacities between 217,151 to 

2,111,000 gpd (5,170 to 50,250 bpd). The Sal-ProcTM system has been tested on TDS 

concentrations ranging from 7,500 to 82,000 mg/L [165]. Silica crystallization and removal is 

not mentioned in any of the literature on the Sal-ProcTM technology, which may indicate that the 

system is not designed to treat silica-saturated water. 

Designed to facilitate zero liquid discharge of concentrated saline brines, the Sal-ProcTM

process has a theoretical recovery of 100%. However, the final 15% of water removed from a 

feed solution are not likely to be captured for beneficial use. Infrastructure requirements for SalProcTM systems may be relatively high, and will likely require significant footprint to 

accommodate chemical reagent storage and product salt storage. The Sal-ProcTM is relatively 

mobile, and may be constructed to operate out of a cargo trailer. Sal-ProcTM is designed to be 

highly modular and readily integrated into other unit processes. 

Energy requirements for the Sal-ProcTM system are unspecified. However, available data 

indicates that the system has a capital cost ranging from $2.3/gpd to $22.1/gpd ($96/bpd to 

$928/bpd), and an operations and management cost of roughly $3.9/kgal to $13.9/kgal ($0.16/bbl 

to $0.58/bbl) [165]. The literature does not provide any indication of serviceable lifetime for the 

process. This proprietary process requires chemical reagents to produce saleable salts, however 

the exact nature of these reagents is not reported with the exception of Ca(OH)2 [167]. The 

process may also require cleaning chemicals, however no reference is made to this affect in the 

literature. Extensive monitoring and operator oversight may be required to optimize reagent 

dosing and recovered salt management. Minimal pretreatment is required to remove organic 

constituents and any micro constituents that may adversely effect the generation of saleable salts 

from the system. A summary of the technical assessment for the Sal-ProcTM process is shown in 

Table 49. 
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Table 49. Summary of technical assessment of Sal-ProcTM process. 

Criteria Description/Rationale 

Industrial status Full-scale application for produced water treatment in Queensland, Australia. 

System produces 21,600 tons of saleable chemicals per year [165]. 

Feed water quality bins Applicable to TDS >7,500 mg/L. 

Product water quality As recovery is pushed towards zero liquid discharge (100%) the product water 

will become difficult to recover for beneficial use and of low quality. 

Production efficiency 

(recovery) 

Theoretical recovery is 100%. 

Infrastructure 

considerations 

Operational footprint may be relatively large to accommodate for chemical 

reagent and product chemical storage, as well as cleaning chemical storage. 

Individual Sal-ProcTM units may require a relatively low footprint equivalent to 

a cargo container. 

Energy consumption The energy consumption is currently unknown. 

Chemicals Chemicals may be required for pretreatment. SARO systems will likely require 

antiscalants. Chemical reagents, particularly Ca(OH)2, required to facilitate 

chemical crystallization create significant chemical demand. 

Life cycle As an emerging technology, life cycle information is not yet available. 

O&M considerations High level of monitoring and control required. 

High level of skilled labor required to operate Sal-ProcTM process. 

High level of flexibility: easy to adapt to highly varying water quality and 

quantity. 

Highly robust process. 

Reliability needs to be demonstrated through long-term operation. 

Types of energy required: electrical. 

Overall costs The capital and construction costs of Sal-ProcTM systems are site specific. Cost 

estimates for capital cost of this process are $2.3/gpd to $22.1/gpd ($96/bpd to 

$928/bpd), and operations and management cost are roughly $3.9/kgal to 

$13.9/kgal ($0.16/bbl to $0.58/bbl). 

Pre-and post treatment No or minimal pre-treatment such as settling, prescreen, or cartridge filtration 

to remove suspended solids and organic matter. Salts may be selectively 

removed from the feed solution to produce water quality suitable for surface 

discharge. 

Concentrate 

management or waste 

disposal 

Any remaining brine stream will require disposal through injection. 

Applicability for 

produced water 

treatment 

Excellent – Capable of near zero liquid discharge operation, and may produce 

a marketable salt from the concentrated brine. Large chemical demand may 

limit application to centralized treatment facilities.

Note: 1 barrel = 42 US gallons 

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Post-treatment and Miscellaneous Treatment 

SAR and Other Nutritious Minerals Adjustment 

Some produced water and/or treated water such as RO product water have high sodium 

and low calcium and magnesium concentrations. High sodium concentrations in waters reduce 

the permeability of clay-bearing soil and adversely affect the soil structure. Water that lack 

secondary macronutrients such as calcium, magnesium, and sulfate can cause deficiency 

symptoms in crops that may need remediation by fertilization. Therefore, the water has to be 

properly treated to prevent adverse effects to distribution systems, soils, and crops. 

Sodium adsorption ratio (SAR), along with pH, characterizes salt-affected soils. It is an 

easily measured property that gives information on the comparative concentrations of sodium 

(Na+

), calcium (Ca2+), and magnesium (Mg2+) in soil solutions. SAR is calculated using the 

following equation: 

2

( )/)(

)/(

2 2 LmeqMgCa

LmeqNa SAR  





 

When the SAR rises above 12 to 15, serious physical soil problems arise and plants have 

difficulty absorbing water. Table 50 and Table 51 provide specific information on tolerance of 

plants and soils to SAR.

Table 50. Plants tolerance to SAR. 

Tolerance SAR of irrigation water Crop 

Very sensitive 2-8 Fruits, nuts, citrus, avocat 

Sensitive 8-18 Beans 

Moderately tolerant 18-46 Clover, oats, rice 

Tolerant 46-102 Wheat, barley, tomatoes, beets, tall wheat grass, 

crested grass 

Source: Extracted from the Australian Water Quality Guidelines for Fresh & Marine Waters (ANZECC) 

Table 51. SAR Hazard of irrigation water 

SAR Notes 

None < 3.0 No restriction on the use of recycled water 

Slight to 

moderate 

3.0 - 9.0 From 3 to 6 care should be taken to sensitive crops. 

From 6 to 8 gypsum should be used. Not sensitive crops. 

Soils should be sampled and tested every 1 or 2 years to determine whether the 

water is causing a sodium increase 

Acute > 9.0 Severe damage. Unsuitable. 

High SAR water can be blended with other source waters for remineralization. There are 

also a variety of treatment methods that can be used to add hardness back to desalinated water 

[102]; these may include addition of lime or contact filtration through limestone (calcite or 

dolomite) filters. The addition of slaked lime (calcium hydroxide) to produced water can provide 

calcium and alkalinity (i.e., hydroxide alkalinity) as well as to adjust product water pH. When 
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adding lime to water, it is important to consider that the solubility of calcium carbonate depends 

on pH, temperature, and ionic strength. Lime may not dissolve easily and may cause residual 

turbidity, which is a disadvantage of this approach. 

It should be noted that adding calcium and magnesium to produced water does not reduce 

sodium, but changes the ratio of sodium to other salts. Although the SAR is decreased by adding 

hardness, the produced water becomes more saline with the sodium salt still dissolved in the 

water. This approach is not likely to work with CBM product water that is sodium bicarbonate 

type. The added hardness (calcium) will combine with carbonate from the CBM water and 

precipitate out as calcium carbonate (lime). 

SAR treatment may require the addition of acid (e.g., H2SO4) to help degassing carbonate 

and dissolve the lime and produce the desired hardness concentration. Warm water however can 

slow down the rate of lime dissolution. This method is commonly used to add hardness and 

alkalinity to water to make it more stable and for corrosion protection. 

Besides SAR adjustment of produced water, land irrigated by high SAR produced water 

can be treated with gypsum and other soil supplements between irrigation cycles (e.g., conducted 

by Williams [3]). The technical assessment of SAR adjustment and addition of other minerals for 

produced water disposal and reuse is summarized in Table 52. 

Table 52. Summary of technical assessment of SAR adjustment and addition of other 

minerals. 

Criteria Description/Rationale 

Industrial status Industrialized technology. Have been used for produced water management.

Feed water quality bins Not applicable. 

Product water quality Not applicable. 

Production efficiency 

(recovery) 

Not applicable. 

Infrastructure 

considerations 

No specific requirement. 

Energy consumption Energy requirement is low. 

Chemicals Chemicals required, such as lime, limestone, acid or other mineral salts, etc. 

Life cycle Same as treatment plant. 

O&M considerations Chemical handling. 

Overall costs Overall cost is low, and depending on the chemical used. 

Pre-and post treatment Not applicable. 

Concentrate management 

or waste disposal 

Not applicable. 

Applicability in produced 

water treatment 

Excellent for produced water treatment. 

Note: 1 barrel = 42 US gallons 

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Constructed Wetlands 

The development of constructed wetlands started approximately 40 years ago to exploit 

the biodegradation ability of plants [19]. Wetland treatment systems utilize natural filtration 

systems to remove suspended matter, organic matter, nutrients, metals, and certain pathogens. 

Constructed wetlands allow vertical and horizontal flow of water through the system. In vertical 

flow system (Figure 48) water flows through layers of soils and gravels. It is an aerobic process 

used primarily to remove organic matter and nutrients by natural bacteria in an aerobic 

environment. 

Figure 48. Vertical flow constructed wetland. 

The horizontal flow constructed wetland system (Figure 49) is a facultative aerobic or 

anaerobic process, depending on the time and frequency of inundation, where water flows from 

one side of the system to the other. This type of constructed system is typically used to remove 

biological organic matter, to disinfect, to filter finely, and remove specifically by precipitation, 

ionic exchange, or adsorption [19]. 

Figure 49. Horizontal flow constructed wetland. 

Constructed wetlands also provide an approach to treat raw produced water or as posttreatment to further clean treated water. Research sponsored by Marathon Oil Company in 2000 

involved construction of an artificial sedge wetland system to treat CBM produced water. The 

purpose of the project was to determine if constituents concentrated in CBM produced water, 

mainly SAR, iron, and barium, could be treated cost-effectively. The flowrate into the wetland 

system in that study was designed to be 30-40 gpm (approximately 1 bpm). Results after one 

year of operation indicated that the wetland system could effectively treat iron and possibly 

barium, but not change SAR. A report by Montana State University further supported these 

results, concluding “clean water is needed to supplement sodicity and saline treatment by 

vegetation and soil (Cited from All Consulting report, [168]). 

Leon et al [169] proposed that for produced water with high chloride content, wetlands 

can be used as a natural evaporating system, in which halophyte plants uptake water and 

evapotranspire it, reducing water volume and the associated costs by effluents reinjection. For 

produced water with organic compounds content, wetlands are proposed to be used as treatment 

systems. Wetlands could be designed for specific desired results, depending on produced water 

quality and prevalent environmental conditions [169]. 
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The advantage of the constructed wetland systems includes low construction and 

operation costs (Cooper, et al., 1996, cited from All consulting report [168]), approximately 1 to 

2 cents/bbl. Kuipers estimated the constructed wetlands costs from 1 to 7 cents per barrel per day 

[170]. Constructed wetland systems are easy to maintain, but they have slow operation rate. The 

long-term use of artificial wetlands for organic removal treatment is 20 years and provides 

excellent wildlife habitat. 

Constructed wetlands have several constraints on their usefulness: 1) Wetlands require a 

large amount of land per unit volume of water; 2) A sufficient supply of water is necessary to 

support the wetland; 3) The source and quality of wastewater may require pretreatment, in some 

agricultural and municipal cases wastewater must be pre-treated before entering a treatment 

wetland (Gopal, 1999, cited from [171]); and 4) Periodic release of captured contaminants during 

high flow periods or periods when vegetation decomposes may occur. 

A limitation of wetlands in cold climates is that primary function may be minimal during 

winter months. A possible solution to this problem would be to spray the inflow water in the air. 

This would cause the fresh water to freeze (some would evaporate as well), and the remaining 

water would be more concentrated in respect to the salts [171]. 

For engineered wetlands, the change in TDS due to significant evapotranspiration is 

important to consider in a hot and dry climate [172]. Desalination process located downstream 

from the engineered wetland may be needed to reduce the TDS concentration to required effluent 

concentrations. 

Various plant types have been studied and identified for salt tolerance and uptake, as well 

as for their quality as forage for livestock. A possible strategy to aid in processing CBM product 

water is to construct a wetland composed of a variety of halophytic plants which have dense 

fibrous root systems, uptake salts and sodium, can be used as forage, have high 

evapotranspiration and water use rates, or a combination of these traits. 

Wetlands may have significant ecological and environmental impact. They provide areas 

that can be utilized by wetland birds and animals and aquatic life. Wetlands can also be utilized 

for livestock and wildlife watering purposes [170]. On the other hand, the contaminants in CBM 

produced water may affect fish and wildlife. For example, the research conducted by the USGS 

has demonstrated acute and chronic sodium bicarbonate toxicity to aquatic species. The CBM 

produced water discharges containing selenium in concentrations above 2 mg/L may cause 

bioaccumulation in sensitive species [173]. In addition, if the wetlands are constructed as part of 

direct discharge, they will change habitat from increased flows and increased erosion. Impacts to 

downstream users due to direct discharges would be higher with increased flows during 

traditional low flow periods and increased sedimentation from erosion. The technical assessment 

of constructed wetlands for produced water disposal is summarized in Table 53. 

Table 53. Summary of technical assessment of constructed wetlands. 

Criteria Description/Rationale 

Industrial status Industrialized technology. Have been used for produced water management.

Feed water quality bins In general < discharge limit if surface discharge applied. Salt concentration 

of water in which halophytic plants are grown ranged from 2 to 6 % 

(corresponding to 20,000 to 60,000 mg/L, EC 30 - 90 dS/m) [171]. 

Product water quality Not applicable. 

Production efficiency 

(recovery) 

Variable, mainly discharge technology. 
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Table 53. Summary of technical assessment of constructed wetlands. 

Criteria Description/Rationale 

Infrastructure 

considerations 

Large land area requirements. Pipeline, monitoring wells or boreholes are 

required. 

Energy consumption Energy requirement is low. Water may need to be pumped to the wetlands. 

Chemicals No chemicals required. 

Life cycle Site specific, may be 20 years for organic matter decomposition. 

O&M considerations Annual operation and maintenance is assumed to consist of repairs to the 

piping and wetlands sediment removal requiring equipment for one week 

and 22.5 days labor [170]. 

Overall costs Capital costs are highly variable and dependent on location. O&M cost is 

estimated $0.01-0.07/bbl [170]. 

Pre-and post treatment May need treatment to remove certain contaminants. 

Concentrate management 

or waste disposal 

Sludge needs disposal if wetland has been designed for periodic sludge 

removal. 

Applicability in produced 

water treatment 

Excellent for produced water treatment and disposal. 

Note: 1 barrel = 42 US gallons 

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Infiltration Ponds 

Infiltration impoundment (aka holding pond, recharge pond) is a common method of 

handling CBM produced water. These impoundments are typically unlined; in some cases, the 

bottom surface of an impoundment area may contain key trench-type excavations or closely 

spaced boreholes to enhance infiltration. Evaporation also may be enhanced by atomizers placed 

on towers situated on floating islands, with spray from these units directed above the water 

surface only [174]. 

Infiltration ponds also have some treatment function to lower TDS by a settling removal 

mechanism or by water infiltration through a pre-fabricated pond liner. Nutrient uptake is also 

possible through various biological processes that could facilitate additional uses [19]. 

In Wyoming, approximately 3,000 infiltration ponds are either currently in use or are in 

the permitting stage [175]. Similar use of infiltration ponds in Montana is expected as CBM 

development expands. Infiltration ponds have several advantages. They are an inexpensive 

means of disposing of produced water, and allow more flexibility in pumping rates for the 

developer/operator. Also, the produced water, which comes from primary aquifers in the area, 

helps recharge the shallow ground-water system [175]. In areas with limited water supplies, this 

technology would be most applicable to increase declining groundwater systems to help 

supplement various water uses. 

The use of recharge ponds to replenish depleted aquifers would be very site specific and 

would require extensive evaluation [19]. The infiltration ponds also have several potential 

disadvantages. The infiltrated water may not move vertically into the original deep aquifers, but 

rather tends to infiltrate to shallow zones or move laterally. As the sodium-bicarbonate water 

moves through the shallow weathered bedrock, a series of chemical reactions may increase the 

salt load in the water and detrimentally impact shallow aquifers or streams. Predicting changes in 

water quality is an integral part of permitting these ponds [175]. 

Researchers at the Montana Bureau of Mines and Geology are developing methods to 

assess proposed CBM infiltration pond sites and to test and calibrate those methods with field 

research. This will determine what criteria will be needed for the appropriate siting of infiltration 

ponds. The technical assessment of infiltration ponds for produced water disposal is summarized 

in Table 54. 
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Table 54. Summary of technical assessment of infiltration ponds. 

Criteria Description/Rationale 

Industrial status Industrialized technology. Have been used for produced water management. 

Feed water quality bins Meeting water recharge standards. 

Product water quality Improved quality through infiltration, including different removal rates of 

organic matter, suspended solids, nutrients and metals. 

Production efficiency 

(recovery) 

Variable and site specific. Water balance studies on existing reservoirs in 

Powder River Basin indicate that rates of infiltration range from 4 feet to 

more than 20 feet per year, depending on the soil type that underlies the 

impoundments [174]. In areas of sandy soil, the rate of infiltration may be 

considerably higher than 20 feet per year. An average rate of infiltration of 

8 feet per year is assumed for the regional modeling analysis. This analysis 

estimated that 15% of the water that is discharged to impoundments would 

resurface and enter the surface drainage system. Of the remaining 85%, 

about 67% would infiltrate to recharge the shallow groundwater system, and 

the remaining 33% would evaporate [174]. 

Infrastructure 

considerations 

Large land area requirements. Pipeline, monitoring wells or boreholes are 

required. 

Energy consumption Energy requirement is low; water may need to be pumped. 

Chemicals No chemicals required. 

Life cycle Depending on well development. 

O&M considerations Annual operation and maintenance is assumed to consist of repairs to the 

piping, pumps and clogged sediment removal. 

Overall costs Capital costs are variable and site specific. Typical cost was estimated 

$0.01-0.02/bbl [170]. 

Pre-and post treatment May need treatment to remove certain contaminants. 

Concentrate management 

or waste disposal 

Removed sludge needs disposal. 

Applicability in produced 

water treatment 

Excellent for produced water disposal. 

Note: 1 barrel = 42 US gallons 

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Big Cat Energy Corporation: Aquifer Recharge Injection Device (ARID) 

 The aquifer recharge injection device (ARID) is a separation technology that allows for 

the production of natural gas from a coal seam without producing any water at the surface. In this 

system the producing well is also able to function as the disposal well for produced water. ARID 

consists of an aluminum mandrel that is installed between a producing coal seam and a 

stratigraphically higher saline aquifer. The cylindrical mandrel has several rubber o-rings that are 

used to seal the mandrel, like a plug in the borehole. The mandrel has four machined ports; these 

four ports are used for water and gas conveyance, a pump cable, and a transducer. A submerged 

pump is attached to the bottom of the mandrel with a pipe. Water is pumped from the bottom of 

the borehole the top of the mandrel plug. Water is then allowed to fill up the top of the plug and 

seep into a previously identified saline aquifer through perforations in the well casing. A 

watertight seal at the wellhead ensures that all of the water pumped from the producing zone is 

forced into the discharge aquifer. During pumping CBM gas accumulates in the headspace 

created between the mandrel and water level of the coal seam. This gas is recovered through the 

mandrel with a pipe that leads to a surface compression station. A schematic drawing of ARID is 

provided in Figure 50. 

Figure 50. Operational diagram of the ARID process (Source: [176]). 

 

The ARID system is being marketed for the Powder River Basin. Big Cat Energy Corp. 

claims that it will circumvent many of the NPDES regulations that make it difficult to produce 

out of the Montana portion of the basin. There are no published or verifiable reports on this 

process; however, the device is expected to undergo field trials in 2009 [177]. 

Beyond the Powder River Basin, this simple technology may be employed as a cost 

effective solution for management and disposal of very high TDS water (Bin 5). The limiting 

criterion is the presence of a stratigraphically higher aquifer that has similar natural water 

chemistry to that of the CBM produced water and the necessary assimilative hydraulic capacity. 

Trivial technical literature combined with the absence of field trial data makes it difficult to 

discuss the broader merits and disadvantages of this technology. 

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Membrane Cleaning 

 Researchers at Texas A&M University have performed numerous experiments to 

elucidate the most effective cleaning chemicals to remove UF membrane foulants from the 

treatment of produced water with moderately high salinity and dissolved oil. The cleaning 

efficacy of nine unique micelle based cleaning solutions was tested on three separate polyvinyl 

diflouride (PVDF) polymeric UF membranes. Each unidentified UF membrane was subjected to 

six different bench-scale fouling scenarios with two different feed water flow rates and three 

different transmembrane pressures. Each of the cleaning solutions was developed with various 

types of alkylpolyglycoside derivatives and solid surfactants (such as alpha-olefin sulfonates) in 

the presence of various salt concentrations to achieve a desired oil and water solubility 

characteristic. The exact composition of the various cleaning solutions is not disclosed [178]. 

Experimental results from the Texas A&M study indicate that certain micelle based 

cleaning solutions may be tailored to provide improved cleaning efficacy over acid and base 

cleaning results from a previous study [179]. Burnett [178] reported a flux recovery 

(Jcleaned/Juncleaned) ranging from 1.15 to 7.53, with an average of 2.73 and a standard deviation of 

2.14 for the nine different cleaning solutions. 

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REFERENCES 

[1] M.G. Puder, and J.A. Veil, Offsite Commercial Disposal of Oil and Gas Exploration and 

Production Waste: Availability, Options, and Costs, ANL/EVS/R-06/5. Prepared by the 

Environmental Science Division, Argonne National Laboratory for the U.S. Department 

of Energy, 2006, http://www.ead.anl.gov/pub/doc/ANL-EVS-R-06-5.pdf

[2] J.A. Veil, Costs for Offsite Disposal of Nonhazardous Oil Field Wastes: Salt Caverns 

versus Other Disposal Methods. Prepared for DOE Office of Fossil Energy (April 1997); 

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[147] Drake Water Technologies, Patented Drake Process, 2008, http://www.drakewater.com/

[148] M. Sheedy, Short bed ion exchange technology produces ultrapure water without using a 

mixed bed., 2006, Eco-Tec, Ontario, Canada. 

[149] L. Hausz, Size Does Matter: Evolution of Counter-Current Ion Exchange for Industrial 

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[150] Eco-Tec, Technical Papers, 2008, http://www.eco-tec.com/Library/tech_papers.php

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[164] GeoPure Water Technologies, LLC, Western Wyoming Case Study, 2007, 

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ACRONYMS 

AEM – Anion Exchange Membranes 

AGMD – Air Gap Membrane Distillation 

ARID – Aquifer Recharge Injection Device 

bbl – Barrel (42 US gallon) 

BOD – Biological Oxygen Demand 

bpd – Barrels per day 

bpm – Barrel per minute 

BTEX – Benzene, Toluene, Ethylbenzene, and Xylene 

BWRO – Brackish Water RO 

CBM – Coalbed Methane 

CDI – Capacitive deionization 

CDT – Capacitive deionization technology 

CEM – Cation Exchange Membranes 

CIP – Clean In Place 

COD – Chemical Oxygen Demand 

DAF – Dissolved Air Flotation 

DBP – Disinfection Byproduct 

DCMD – Direct Contact Membrane Distillation 

DGF – Dissolved Gas Flotation 

DP3ROTM – Double Pass, Preferential Precipitation, Reverse-Osmosis process 

ED – Electrodialysis 

EDI – Electrodeionization 

EDR – Electrodialysis Reversal 

EVRAS – Evaporative Reduction and Solidification 

EWP - Electronic Water Purification 

FO – Forward osmosis 

FTE – Freeze/Thaw Evaporation 

gfd – Gallon per square foot per day 

gpd – Gallon per day 

gpm – Gallon per minute 

HEED – High Efficiency Electrodialysis 

HEROTM – High Efficiency RO 

HTE – Horizontal Tube Evaporator 

IGF – Induced Gas Flotation 

IX – Ion Exchange 

MD – Membrane Distillation 

MED – Multiple Effect Distillation 

MF – Microfiltration 

MGD – Million Gallons per Day 

MSF – Multi Stage Flash Distillation 

MVR – Mechanical Vapor Recompression 

NF – Nanofiltration 

NOM – Natural Organic Matter 

NPDES – National Pollutant Discharge Elimination System 
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OTSG – Once-Through Steam Generators 

POTW – Publicly Owned Treatment Works 

RO – Reverse osmosis 

ROSP – Combined RO – Sal-Proc 

SAGD – Steam-Assisted Gravity Drainage 

SAR – Sodium Adsorption Ratio 

SDI – Silt Density Index 

SEM – Scanning Electron microscope 

SEPCON – Saline Effluent to Products Conversion 

SGMD – Sweeping Gas Membrane Distillation 

SPARRO – Slurry Precipitation and Recycling RO 

SPR – ShockWave PowerTM reactor 

SWRO – Seawater RO 

TDS – Total Dissolved Solids 

TFC – Thin Film Composite (membrane) 

TOC – Total Organic Carbon 

TRPH – Total Recoverable Petroleum Hydrocarbons 

TSS – Total Suspended Solids 

TVC – Thermo Vapor Compression 

UF – Ultrafiltration 

VCD – Vapor Compression Distillation 

VMD - Vacuum Membrane Distillation 

VOC – Volatile Organic Compounds 

VTE – Vertical Tube Evaporator 

WAIV – Wind Aided Intensified Evaporation 

WFRD – Wiped Film Rotating Disk 

ZLD – Zero Liquid Discharge