# An Integrated Framework for Treatment and Management of Produced Water

TECHNICAL ASSESSMENT OF PRODUCED WATER TREATMENT
TECHNOLOGI ES

1 st EDITION



### RPSEA Project 07122-12

November 2009RPSEA Project 07122-12
TECHNICAL ASSESSMENT OF PRODUCED WATER TREATMENT TECHNOLOGIES

1 st

Edition

1 

### TECHNICAL ASSESSMENT OF PRODUCED WATER TREATMENT
TECHNOLOGIES

This report presents a comprehensive literature review and technical assessment to evaluate existing and emerging technologies that ha ve 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 di scharge (ZLD). This assessment considers pretreatment, desalination, post-treatment, and concentrated waste disposal to meet the required water quality standards for be neficial 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/pro cesses for produced water treatment. This
document can be used to evaluate various treatmen t processes in a generic fashion even if their
vendors are not liste d in the report. The report was developed as part of a co llaborative 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 a nd assessed in the study. The technologies are classified into stand-alone technologi es and com bined treatment processes.

Stand-alone/primary Mult i-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: OPUS TM

o Eco-Sphere: Ozonix TM

o GeoPure Water TechnologiesRPSEA Project 07122-12
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2 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-Proc TM , ROSP, and SEPCON Commercial Treatmen t IX-based processes

o EMIT: Higgins Loop

o Drake: Continuous selective IX process Eco-Tech: Recoflo® compressed-bed IX

process

o Catalyx/RGBL IXRPSEA Project 07122-12
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3 EVALUATION CRITERIA
This review broadly documents state-of-the -art research and development efforts in produced water treatment. The technologies and c onfigurations identified in the review are technically assessed in terms of several im portant criteria, which are summarized in Table 1

. The technologies are evaluated based on water quality bins: (i) feed water quality, and particularly salinity and const ituents of concern for treatm e nt processes (e.g., hydrocarbons, suspended solids, hardness, silica, barium, ir on, manganese, boron); (ii) product water quality and its relation to water quality requirements fo r different produced water discharge regulations and beneficial use applications, including surf ace water discharge, agriculture irrigation, life stock irrigation, and USEPA dri nking water standards. Another key criterion in the technical assessment is production efficiency in terms of pr oduct water recovery, whic h 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, encl osure and footprint, re liability, robustness, costs, O&M considerations, pretreatment and post treatment requirements, and concentrate management options. The applicability of th e 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 ther e may be some factors that limit its
broad utilization for treatment of CBM produced water.

 Excellent – the technology can be used fo r 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 poten tial users with an objective and unbiased
technical assessment. In additi on to the description of the te chnology theory and key technical
and economic considerati ons listed in Table 1, th e report summarizes impor tant findings from field trials, pilot studie s, 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 mate rial, including peer-revie wed 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, manufact urer brochures are the only av ailable source for information.RPSEA Project 07122-12
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4 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 (includi ng supplier names), minimum and maximum plant size Feed water quality bins Applicable TDS range, types of water chemistry makeup, constituents of concerns including: hydrocar bons, 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 me tals, 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 th e process and replacement needs

O&M considerations Levels of monitoring a nd 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 th e 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)RPSEA Project 07122-12
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5 WASTE DISPOSAL COST
Because waste disposal is a common consider ation for all water treatment technologies, the costs of waste disposal are discussed here pr ior to the review of water treatment technologies. Waste disposal costs strongly depe nd on the location of and distance of the disposal facility from the production site, disposal method, the type of wa ste (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 commer cial 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 availa bility 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 radio active material (NORM),

• Oil-based muds and cuttings,

• Produced water,

• Tank bottoms, and

• Water-based muds and cuttings.

The different waste management or dis posal 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 brie fly 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]. Th is implies that the disposal co sts of more concentrated or solidified wastes after produced water treatment mi ght be more costly th an 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, an d a landfill facility in Louisian a. The lowest costs are charged by one cavern operator in Texas as well as several injection facilities in Oklahoma. By far, theRPSEA Project 07122-12
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6 most common commercial disposal method fo r produced water is in jection, 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 signifi cant 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 in jection. Costs range be tween $5/bbl and $10.50/bbl. Today, evaporation of produced water is most widely practiced in Wyoming (seven companies), followed by Colorado (four companie s), Utah (four companies), and New Mexico (three companies). Except in one case, the di sposal costs range betw een $0.40/bbl and $3.95/bbl. One company in Colorado charges $84/bbl. Burial in landfills is available for pr oduced water across the nation. However, solidification, which is genera lly required, drives up the cost s. 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 hi gher ranges of up to $128/ton and $250/ton, respectively. Burial of produced water in co mmercial pits is not widely reported. Three companies, in Oklahoma, Utah, and Wyomi ng, 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 NPDE S permit was reported by three companies in Pennsylvania and one company in Wyo ming. The costs range between $0.045/gal and $0.055/gal ($2.25/bbl and $2.75/bbl) in Pennsylvania, and betw een $2.50/bbl and $3.50/bbl in Wyoming. All four companies apply treatment prio r to discharge. Two f acilities in Pennsylvania discharge produced water to a POTW for a di sposal fee of between $0.015/gal and $0.050/gal ($0.75/bbl to $2.50/bbl). Land application of produced water is offere d 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 Californi a charges $5/bbl. Another company in Oklahoma indicates a cost of $25/load. Th ermal treatment of produced water is offered by Clean Harbors
Environmental Services at its Deer Park fa cility. Costs range be tween $0.02/lb and $0.20/lb ($40/ton to $400/ton, or $10.5/bbl to $105/bbl).RPSEA Project 07122-12
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7 REVIEW AND ASSESSMENT OF WATER TREATMENT TECHNOLOGIES
The following section presents a descrip tive write-up corresponding to each technology,
based on the list of cr iteria included in Table 1 . A detailed tabular summ ary, or synopsis, of th e 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 f ilters, intermittent filt ers, 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 tr eated flows downward over the media and over time generates a microbial film on the surface of the media ( Figure 1 ). The media facilitates biochemical oxi dation/rem oval of organic constituents. This is an aerobic process and aerobic conditi ons are maintained by pumps and fans in the system. The thickness of the microbial layer c ontinues 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 effl uent [4]. Media should have high surface area per unit volume, be durable , and inexpensive. The t ype 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 a nd will not clog when sloughing occurs [5].

Figure 1. Schematic drawing of a biological aerated filter.

BAF can remove oil, suspende d solids, ammonia, and nitr ogen, chemical oxygen demand (COD), biological oxygen demand (BOD), iron, manganese, heavy metals, soluble organics, trace organics, and hydrogen sulfide. Iron and ma nganese removal in BAFs is mainly due to chemical oxidation rather, no t a biological process. Since BAFs do not remove dissolved constituents, however, high concentrations of sa lts can decrease the e ffectiveness 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 le vels 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.RPSEA Project 07122-12
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8 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 treatm ent [7]. Informal versions of BAFs require minimal equipment, can be made by flowing wate r 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 ra te 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 of f 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 upstr eam 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 remova l. 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 aer ation, and distribution nozzles. The estimated energy demand for BAFs is 1 to 4 kWh/day. No chemicals are nece ssary [5]. A summary of the BAF assessment is provided in Table 2

.

Table 2. Biologica l 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 concentra tions 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 upstrea m and downstream sedimentation, therefore, they have a large footprint and are not very mobile or modularRPSEA Project 07122-12
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9 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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10 Hydrocyclone
Hydrocyclones are used to separate solids from liquids based on the density of the

m aterials 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
determ ines the performance and separating capab ility of the hydrocyclone. Hydrocyclones can be made from metal, plastic, or ceramic a nd have no moving parts. The hydrocyclone has two exits, one at the bottom, called the underflow or re ject for the more dense fraction and one, called the overflow or product at the top for the less dense fraction of the or iginal 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 particul ates 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 solubl e 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 Ba rnett Shale play [15]. In this rese arch study, hydrocyclone s 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 on ly piece of equipment necessary. There are no energy requirements unless the plant setup requir es a forwarding pump to deliver water to the hydrocyclone. Depending on the size and configur ation of the hydrocycl one, a large pressure drop can occur across the hydrocyclone. The waste generated from a hydroc yclone is slurry of concen trated solids. This is the only residual that requires dispos al. A summary of the hydrocycl one assessment is provided in

Table 3

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11 Table 3. Hydrocyclone Assessment

Criteria Description/Rationale

Industrial Status Hydrocyclones have been widely u sed for produced water. They are mainly used for oil/water separa tion and can also be used for particulate removal. Feed water quality bins Applicable to all TDS bi ns, independent of salt t ype and concentration. High organic concentrations. High oil and grease or high particulate concentrations. Product water quality Can reduce oil a nd 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 inle t 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 othe r constituents from feed water. Concentrate management or waste disposal Disposal required for slurry.

Note: 1 barrel = 42 US gallons

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12 Flotation
Flotation is a process in whic h fine gas bubbles are used to separate small, suspended particles that are difficult to sepa rate by settling or sedimentation ( Figure 3 ). Gas is injected into
the wate r to be treated and partic ulates 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 pr oduced water [16-18]. Gas flotation technology is subdivided into dissolved gas flota tion (DGF) and induced gas flotation (IGF). The two tec hnologies differ by the method used to generate gas bubbles and
the resultant bubble sizes. In DGF un its, 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. IG F technology uses mechanical shear or propellers
to create bubbles that are intr oduced into the bottom of the flot ation chamber [14]. Coagulation can be used as a pretreatment to flotation. The efficiency of the flotation process depe nds 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]. Flotati on cannot removal soluble oil constituents from water. Treatment costs are estimated to be $0.60/m 3 [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 presen t, 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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13 Table 4. Flotation Assessment.

Criteria Description/Rationale

Industrial Status Widely used for produced water tr eatment, 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 H 2 S [21] Production efficiency (recovery) High recovery, nearly 100%

Infrastructure considerations Dissolved air flotation requires an external pressurized tank Energy consumption Energy is required to pr essurize the system to di ssolve 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 require d for the sludge generated from
flotation. Note: 1 barrel = 42 US gallons

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14 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 back washed to remove large particulates trapped
between the voids in the media. Typically, these proce sses can be gravity fe d and do not require an energy supply, except during backwash. Adsorbents are capable of removing ir on, manganese, total organic carbon, BTEX compounds, heavy metals, and oil from produced wate r. Adsorption is generally utilized as a unit process in a treatment train rather than as a st and-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 operati onal costs for adsorptive processes. When all active site of the adsorptive material have b een consumed, the material must either be regenerated or disposed of. Rege nerating the materials will result in a liquid waste for disposal. Solid waste disposal is necessary when the materi al needs to be replaced entirely. A summary of the adsorption assessment is provided in Table 5

.

Table 5. Adsorption Assessmen t

Criteria Description/Rationale

Industrial status Adsorption is commonly used for treatment of produced water

Feed water quality bins Applicable to all TDS bi ns, independent of salt t ype and concentration. Can remove iron, manganese, TOC, BTEX, and oil.
Zeolites can also be used to exch ange 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 replaceme nt 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 n ecessary 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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15 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, therefor e filtration can be used for all TDS bins regardless of salt type. Filtration can be used to remove oil and gr ease and TOC from produced water. Removal efficiencies can be improved by employing coagul ation 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 extensiv ely for produced water treatment. Multiple vendors available that market filtration technologies specifically for produced water treatment. Feed water quality bins Applicable to all TDS bi ns, independent of salt t ype and concentration. Product water quality > 90% oil and grease removal Production efficiency (recovery) Nearly 100% water recovery is achie ved with filtration; some filtrate may be used for backwashes. Energy consumption Minimal energy is require d 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 replaceme nt 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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16 Oxidation

Chemical oxidation treatment can be used to remove iron, manganese, sulfur, color, tastes, odor, and synthetic orga nic chemicals. Chemical oxida tion relies on oxidation/reduction reactions, which consist of two half-reactions: th e 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 occu r together since free el ectrons cannot exist in
solution and electrons must be conserved [23]. Oxidants comm only used in water treatment applications include chlorine, chlorine di oxide, permanganate, oxygen, and ozone. The appropriate oxidant for a given application depends on many fact ors including raw water quality, specific contaminants present in the water, and local chemical and power costs [23]. Chemical oxidation is well established, reliable, and requi res minimal equipment [24]. Oxidation can be employed to remove organics and some inorga nic compounds like iron and manganese from produced water. The removal or oxidation rate may be controll ed by applied chemical dose and
contact time between oxidants and water. No pretreatment is required for oxidati on. Solid separation post- treatm ent 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 a ssessment is provided in Table 7.

Table 7. Ox idation 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 a ll TDS bins, independent of salt type and
concentration. Product water quality Depends on type of oxidant used Production efficiency (recovery) 100% recovery.

Infrastructure considerations Chemic al 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 meteri ng 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 n ear 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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17 Settling
Settling can be achieved using a pond or a basin. In this process, particulates are removed by gravity settling. Settling ponds require a larg e footprint and environmental mitigation to protect wildlife. Settling ponds w ill most likely be used in combination with other treatment processes. There are no chemical requirement s but chemicals can be used to enhance
sedimentation. Infrastructure re quirements include liners. Sett ling ponds are used to remove large particulates from water sources. The degr ee 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. Th e volume required depends on the hydraulic residence time required for the desired level of
contaminant removal. Energy consumption None, unless pumping is re quired 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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18 Ultraviolet Disinfection
UV radiation disinfection is a popul ar form of primary disinfec tion because of its ease of use, no need of chemicals, and no formation of disinfection byproduct (D BP). Water is pumped through a UV reactor, which is e quipped with an array of UV lamps providing disinfection dosages of 30-50 mJ/cm 2 . As pathogens path through the reactor they are inactivated. They are exposed to the UV light for a predetermined pe riod 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 treatmen t. 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 insi de of quartz lamp sleev es 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 microorgani sms from the UV by suspended solids. This phenomenon is called “shadow eff ect”. UV disinfection does not provi de a disinfectant residual. Therefore, addition of chlorine or chloramine as a secondary disi nfectant might be required [24]. Disinfection is typically the last treatment st ep in most water trea tment 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 TD S bins. May not be suitable for highly turbid

water. Product water quality Inactivation of microbi al 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 invol vement, approximately 5 hours per month. Periodic cleaning and lamp replacement is required.

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19 Table 9. Ultraviolet Disinfection.

Criteria Description/Rationale Pre-and post treatment Will require pretreat ment 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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20 Microfiltration/Ultrafiltration
Microfiltration (MF) has the largest pore size (0.1-3  m) of the wide variety of membrane filtration systems. Ultrafiltrati on (UF) pore sizes range from 0.01 to 0.1  m. In terms of pore size, MF fills in the gap between ultrafiltr ation and granular media filtration. In terms of characteristic particle size, MF range covers the lower portion of the co nventional 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, nanofiltrati on, 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 concentrat e flow. There are also two pump configurations, either pressure driven or vacuum-type system s. 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/ft 2 (gfd) depending on the application. Backwash is usually used to clean the
membranes and it is carried out for short durations (3 to 180 s econds) in relatively frequent intervals (5 min to several-hou r) [23]. The frequency and durat ion of backwash depend on the specific application. A clean in pl ace (CIP) can also be performed as a periodic major cleaning technique. Typical cleaning ag ents 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]).RPSEA Project 07122-12
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21 F actors affecting membrane selection are:

 Cost

 Percent recovery

 Percent rejection

 Raw water characteristics

 Pretreatment

F actors 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 ra w water quality, a coagulant may be added to form pin-sized floc and he lp improve rejection [24].

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22 Ceramic MF/UF membrane

Ceramic ultrafiltration and microfiltration memb ranes 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 ar e mechanically strong, chemically and thermally stable, and can achieve high flux ra tes. Typically, a tubular configur ation is used with an insideout flow path, where the feed water flows insi de the membrane channels and permeates through the support structure to the outside of the modu le. These membranes are typically comprised of at least two layers, a porous suppor t layer and a separating layer, see Figure 5 [28].

Figure 5. SEM m icrographs 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 pa rticulates, organic matter, oil and grease,
and metal oxides. Ceramic membranes alone ca nnot remove dissolved ions and dissolved organics. Pre-coagulation, injection of a chem ical coagulant upstream from the membrane, improves removal efficiencies of dissolved orga nic carbon and smaller particulates. As with
conventional ultrafiltration and mi crofiltration, a strainer or car tridge filter is necessary as pretreatment for ceramic membranes.
Numerous research studies have been c onducted 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 polym eric membranes on oil-containing waters. Ceramic membranes have also been employed co mmercially 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 cera mic 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 back wash and cleaning systems. Ceramic membranes have a higher capital co st than polymeric membranes. The use of ceramic membranes is increasing as more res earch 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 freque nt backwashes; backwash waste will require disposal. If ceramic membranes ar e 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)RPSEA Project 07122-12
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23 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 se ll ceramic membrane products in a variety of sizes, materials of construction, and geometric configurations. Feed water quality bins Applicable to all TDS bi ns, independent of salt t ype 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 pum p, 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 co agulants 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 believe d 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 ar e available at this time for ceramic
membranes. Contact vendor for more information. Pre-and post treatment Straining or cartridge f iltration 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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24 Polymeric MF/UF membrane
Polymeric MF/UF membranes are made from materials like polyacrylonitrile (PAN) and polyvinylidene (PVDF). Because there is a large ma rket for polymeric ultrafiltration membranes, there are many vendors and suppliers for these memb ranes. They are also relatively inexpensive. Typically, package systems are purch ased 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 te st, pressurized air is appl ied 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 perfor mance is necessary to ensure the membrane system is operating at the most effective load ing rate and backwash regime. Membrane life is typically estimated at 7+ years with manufact urer 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 surf ace waters are typically processed for turbidity removal through settling ponds or other treatment sy stems. CIP waste is neutralized and usually
combined with the rest of the waste. A summ ary 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 exte nsively in the municipal water treatment industry. Feed water quality bins Applicable to all TDS bi ns, independent of salt t ype 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 wa ter quality and mode of operation (dead-end vs. crossflow).

Infrastructure considerations A feed tank, feed pum p, 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 co agulants 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).RPSEA Project 07122-12
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25 Table 11. Polymeric MF/UF Membrane Assessment

Criteria Description/Rationale Pre-and post treatment Straining or cartridge f iltration 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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26 REVIEW AND ASSESSMENT OF DE SALINAITON TECHNOLOGIES

Pressure Driven Membrane Technologies

Pressure driven m embrane processes utiliz e hydraulic pressure to overcome the osmotic pressure of the feed solution and force pure wate r (called permeate) to diffuse through a dense, non-porous membrane [35]. The residual feed stream (sometimes called retent ate, concentrate, or reject) is concentrated during the process and ty pically requires disposal. An illustration of the process is shown in Figure 6 . Additional treatment technologies may be employed to further
concentrate the concentrate s tream towards zero liquid discharge ( ZLD). Solutions of higher total dissolved solids (TDS) concentratio ns have greater osmotic pressures, and therefore require more hydraulic pressure to produce permeate. Practi cal limits are imposed on the process by pump energy and component manufactur ing costs associated with operating at hydraulic pressures exceeding 1,000 psig. For this reason, pressure driv en membrane processes are typically utilized
for treatment of saline streams with TDS co ncentrations ranging fr om 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 em ployed in spiral-wound configurations ( Figure 7 ) with membrane materials composed of an asymm etric polyamide or polypiperazine amid active laye r and a polysulfone micro-por ous support in a thin film composite (TFC) structure ( Figure 7 ). Mesh spacers are installed in both th e feed channel and perm eate collection
channels of the membrane module. Feed spacers are required to enhance hydrodynamic turbulences in the channel, which diminish es concentration polarization. Concentration polarization is a phenomenon where the feed solu tion becomes more concen trated at the feedmembrane interface, which results from the pr eferential diffusion of pure water through the membrane. A permeate spacer is required to pr ovide mechanical support to the permeate
collection channel. Reverse osmosis (RO) and nanofiltration (N F) 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]. Globa lly, RO seawater desalination technologies dominate global seawat er desalination with a 58% share of the market and growing [38]. FEED PERMEATE

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27 Figure 7. RO membrane construction. (a) A ty pical spiral wound high pressure membrane element and (b) SEM cross section view of an asymmetric RO membrane.

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28 Seawater Reverse Osmosis
Seawater RO (SW RO) membrane systems are most applicable for feed streams up to 47,000 mg/L TDS, i.e., seawater le vel % [37]. SWRO typically em ploys 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 mu ltivalent ions and molecules, and metals. SWRO membranes are designed to achie ve 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 rejecti ons (<20%) depending on the organic compound’s chemical structure and feed solution physicoche mical 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 th e membranes. Constituents of primary concern for all pressure driven membrane processes include organi c acids, metal oxides, and sparingly soluble salts (e.g. CaSO 4 , CaF 2 , and BaSO 4 ). 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 modera tely robust technology that consistently delivers permeate water devoid of most i norganic constituents. RO memb rane systems may be deployed on a trailer-mounted skid, as shown in Figure 8 , which is highly mobile and modular. SW RO technology has one of the smallest footprints of all the technologi es considered in this report. Depend ing on the chemical composition of the RO feed water, system failu re may occur with changing feed water quality.
Low recoveries associated with SWRO generate relatively large vol umes of concentrated reject water. Residual management costs may be substantial. RO systems have been previously empl oyed for various types of produced water treatment. Early pilot studies were conducted w ithout consideration for adequate pretreatment; subsequently the RO membranes were irreversib ly damaged by foulants [42, 43]. Later, systems with rigorous pretreatment trai ns were employed with RO as a final desalination stage. One study was conducted at an oil fiel d produced water facility in Ba kersfield, 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 membra ne 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 Placer ita Canyon Oil Field, CA in 2000; however, little detail is available on the specifics of testing conditions and system configuration [45]. Recently, num erous 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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29 Figure 8. Trailer mounted membrane testing sk id used at AQWATEC, CSM (Source: [46]).

Table 12. Summary of techni cal 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 la rgely 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, SO 4 ), 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 recove ry 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,

Na 4 EDTA, HCl, Na 2 S 2 O 4 , or H 3 PO 4 Expected lifetime of critical
components Depending on operating conditions, SWRO membranes will require replacement within 3 to 7 years

Infrastructure considerations SWRO requires mini mal operational footprints compared to thermal desalination technologies, and can be highly automated SWRO skids are highly mobile.RPSEA Project 07122-12
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30 Table 12. Summary of techni cal 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 system s 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 fr om $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-pressu re 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 re quire pH stabilization or remineralization. This may be achieved by lime bed contactin g 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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31 Brackish Water Reverse Osmosis
BWRO membranes are designed to achieve moderately high rej ection of dissolved constituents (>94% NaCl), and are most efficient when employed for the tr eatment 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 me tals and divalent ions to a high degree, and have similar limitations as SW RO 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 co mpared 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 r ecovery of BW RO over SWRO reduces concentrated brine generation and disposal costs. Available scientific literature suggests th at 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 pe rformed other experiments to determine the fouling potential and effective cl eaning protocols for BWRO and NF membranes. Seven different membranes (four BWRO membranes, and three NF membranes) were investigated in the study. Feed water was obtai ned from a natural gas production facility in
Eastern Montana and was characterized as br ackish groundwater (5,200 mg/L TDS) dominated by NaCl. A second bench-scale study [49] was conducte d with both CBM produced water (sourced from Walsenburg, Colorado) and oil produced wa ter (sourced from Wellington, Colorado). The purpose of this study was to dete rmine the relative effectivene ss of BWRO and NF membranes for treatment of produced water. Three membrane s were tested in the investigation, one BWRO, and two NF membranes. The CBM produced wate r had 650 mg/L TDS a nd was dominated by sodium (no anion composition was given). A summa ry of the technical assessment for BWRO is
listed in Table 13.

Table 13. Summary of techni cal assessmen t of BWRO

Criteria Description/Rationale Status of technology Mature and robust technology fo r 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 fo r TDS ranging from 500 to 25,000 mg/L, and water containing monovalent (Na, Cl), divalent (Mg, Ca, Ba, SO 4 ), multivalent electrolytes (Fe, Mn), a nd 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 recove ry 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 3kWh/kgal (0.02-0.13 kWh/bbl) of energy to power the system’s highpressure pumps.RPSEA Project 07122-12
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32 Table 13. Summary of techni cal 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,

Na 4 EDTA, HCl, Na 2 S 2 O 4 , or H 3 PO 4

. Expected lifetime of critical
components Depending on operating conditions, BWRO membranes will require replacement within 3 to 7 years.

Infrastructure considerations BWRO requires an e quivalent 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 system s 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 includi ng 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-pressu re 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 re quire pH stabilization or remineralization. This may be achieved by lime bed contactin g 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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33 Nanofiltration

NF m embranes 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 me mbranes are designed to reject contaminants as small as 0.001 μm. This a llows NF to achieve high rejection of divalent ions, metals (>99% of MgSO 4 ), 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 applic ation of scale inhibitors or extensive pretreatment dependi ng on feed water quality. The energy required for NF membranes to perf orm 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 bot h pilot- and bench-sc ale for treatment of produced water [44, 48, 49]. The pilot-scal e 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 tec hnical assessmen t of NF

Criteria Description/Rationale Status of technology Mature and robust technology for wa ter 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, SO 4 ) electrolytes, multivalent metals (Fe, Mn), and radionuclides. Also applicable for specific classes of organic compounds. Product water quality NF permea te 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 recove ry 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,

Na 4 EDTA, HCl, Na 2 S 2 O 4 , or H 2 O 2

. Expected lifetime of critical
components Depending on operating conditions, NF membranes will require replacement within 3 to 7 years.RPSEA Project 07122-12
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34 Table 14. Summary of tec hnical 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 includi ng 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-pressu re 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, a nd 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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35 Electrochemical Charge Driven Membrane Process

Electrodialysis / Electrodialysis Reversal
Electrodialy sis (ED) and elec trodialysis reversal (EDR) are electrochemical charge driven separation processes in which dissolved ions are se parated from water through ion permeable membranes under the influence of an electrical potential gr adient. 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 me mbranes (CEM) arranged in an alternating mode between anode and cathode ( Figure 9 ). The positively charged cations

m igrate toward the cathode, pass the cation-ex change membrane, and rejected by the anionexchange membrane. The opposite occurs when th e 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 allowi ng 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 + Cl

Cl

Cl

Cl

Na + 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 typi cally used in desalina tion of brackish water (up to about 8,000 mg/L TDS for EDR) and not s eawater. 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 seve ral 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 so luble inorganic salts (e.g., CaSO 4 , CaCO 3 ) 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 pretreatme nt of the feedwater with processes such as filtration for suspended solids, softening or pH lowering, and addition of antiscalant into the
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36 Depending on feedwater chemistry, water reco very in ED and EDR can be between 70
and 90%. ED membranes are not as susceptible to degradation by chlorine; ther efore, dosing a
small amount of chlorine to the feed water ca n control biological growth in the system. These
features enable ED and EDR to treat surface and wastewaters having hi gh concentrations of organic materials and microorgani sms 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-charge d 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 r eclaimed water [55, 56]. Laboratory experiments have been conducted to investigate th e 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 pr ototype to treat CBM produced wate rs collected from the Powder River basin production field near Sherida n, 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 soli ds was achieved [57]. At a scale of treatment exceeding 0.336 MGD (8,000 bbl/day) produced water, total costs were estim ated 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 stab ilization 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. Synt hetic water was used to simulate produced water qualities in CO, TX, and WY (TDS in the ra nge 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 treatm ent 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 treatme nt 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 pa rticulate 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 HEED TM 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 requ ired. A summary of the technical assessment of ED and EDR is
listed in Table 15

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37 Table 15. Summary of technica l assessment of ED and EDR

Criteria Description/Rationale Status of technology Mature and robust technology fo r 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 TD S < 8,000 mg/L, and treat all types of water chemistry makeup. Product water quality Product wa ter quality depends on ED stages, can achieve over 90%.
Poor removal of non-char ged 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 infr astructure 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 flex ible 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 sp ecific 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 remineraliza tion 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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38 Electrodeionization
Electrodeionization (EDI) is a commercial desalination technology that combines ED and
conventional IX technologies. It is us ed for the production of ul tra-pure deionized water, especially in the semiconductor industry. The principle of th e process is illustrated in Figure 10

. A m ixed-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 incr ease 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 i ons in the resins. The final result is completely deionized water as a product. The IX resins are regenerated vi a water splitting under curre nt. 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 me tal hydroxide in EDI stack is a serious problem as a result of metal ions reactin g 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 compar ed to other membrane processes.
No further assessment was conducted on EDI because of the limited information in the literature and its poor potential appli cation in produced water treatment.

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

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39 Thermally Driven Membrane Process

Membrane Distillation

Mem brane distillation (MD) is a novel ther mally 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 tr ansfer is a vapor pre ssure gradient between
a feed solution and the distillate , and is the only membrane pro cess that can maintain process performance (I.e., water flux and solute rejection) almost inde pendently of feed solution TDS concentration. MD is most likely capable of producing ultra-pure water at a lower cost compared to conventionally distillation processes. Memb rane materials commonly employed for MD include polytetrafluorethylene (PTFE), polyp ropylene (PP), and polyvinylidenedifluoride (PVDF). MD membranes may be p ackaged in either flat-sheet or hollow-fiber configurations. MD may be operated in four basic configur ations: 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 aque ous solution flows counter-currently on the opposite side of the membrane. Molecules of wate r evaporate and diffuse through the pores of the membrane. Upon contact with the cold di stillate solution on the product side of the membrane the vapor condenses and is assimilate d into the distillate solution. AGMD works on a similar principle as DCMD; however, instead of a c ooler 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 co ndenses 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 princi ples of MD. A warm f eed stream containing
various non-volatile solu tes 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 th at 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, SiO 2 , B, and heavy metals) is 100%;RPSEA Project 07122-12
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40 however, compounds with higher volatility than water, such as BTEX and other organic compounds, will diffuse preferentially faster th rough the membrane. As a standalone process MD may be capable of achieving similar wa ter 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 por es of the MD membrane and cause pore flooding, which results in a substantial reducti on in membrane solute rejection. Chemical demands for MD processes are similar to that re quired for pressure-driven membrane processes, however foulants and scale laye rs are more easily removed from the membrane because they are not physically compacted onto the membrane su rface. 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 gradie nt may be harvested from low-grade waste heat generated from comp ressors, pumps, etc. and does not represent a significant operational cost. System maintenance is similar to that of pressure driven proce sses, 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 resist ant 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 pre ssure driven system w ith equivalent capacity. MD is an extremely flexible technology for most variations in feed water quality and quantity; however, the introduction of any surfactan t into the feed soluti on will adversely affect the process. As with many memb rane technologies, MD modules can be readily integrated on mobile platforms and are highly modular. A summa ry of the technical assessment for MD is
listed in Table 16.

Table 16. Summary of tec hnical assessmen t 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].RPSEA Project 07122-12
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41 Table 16. Summary of tec hnical assessment of MD

Criteria Description/Rationale Energy use MD is a thermally driven pr ocess 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,

Na 4 EDTA, 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 requi red 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 ope rate 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 es timated 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 c onstituents 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 re quire remineralization and pH stabilization. This may be achieved by lime bed contactin g 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 pret reatment 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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42 Osmotically Driven Membrane Processes

Forward Osmosis
Forward osmosis (FO) is an osm otically dr iven membrane process. During FO, water diffuses spontaneously from a stream of low osmotic pressure (the feed so lution) to a hypertonic (draw) solution having a very high osmotic pressure. Unlike RO and NF , FO systems operate without the need for appl ying hydraulic pressure ( Figure 12 ). The membranes used for this proces s are dense, non-porous barriers sim ilar 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 ot her draw solutions composed
of NH 4 HCO 3 , sucrose, and MgCl 2 have been proposed [71]. Du ring 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 pr ominent 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 dr iven 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 sa line 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 generi c FO system for desalination.RPSEA Project 07122-12
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43 FO membranes are capable of rejecting all particulate matter and almost all dissolved constituents (greater than 95% re jection 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 proc ess occurs spontaneously, without the need for applied hydraulic pressure. The hydraulic pressure applied in pressu re driven membrane pr ocesses is responsible for compacting foulants onto the membrane, which substantially intensifies irreversible flux decline. Fouling layers that accumulate on FO me mbranes may be readily removed with cleaning (e.g., increasing cross-flow velocity, osmotic backwa shing) 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 p ackaged in flat sheet or spiral-wound configurations. These packages allow for relatively small process footprin ts, but are still not optim ized 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 b een conducted with FO, and have utilized feed water supplies ranging from seawater and brackis h water to municipal a nd industrial wastewater [67, 73-76]. FO has also been employed in a pilo t 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 tec hnical assessmen t 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 ra nge is controlled by the osmotic pressure
differential between the feed solu tion and draw solution. The TDS range is between 500 mg/L to greater than 35,000 mg/L. FO has equivalent solute rejection perfo rmance to existing pressure driven processes for monovalent and divalent electrolytes, metals, and organics. Product water quality The product of FO is a d iluted 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. Th is is typically accomplished with
RO. FO membranes have similar so lute rejection as NF (>90% TDS, >80% ammonia, low rejection of boron). Recovery Product water recoveries ha ve 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.RPSEA Project 07122-12
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44 Table 17. Summary of tec hnical 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,

Na 4 EDTA, 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 contro l 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 ope rate 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 requi red 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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45 Hybrid Membrane Technologies
Numerous methods have been proposed to e nhance recovery and minimize concentrated brine volume generation resulting from membra ne desalination processes. Many of these methods couple multiple stages of membrane-b ased treatment proce sses with intermittent chemical precipitation or caustic addition. These processes include: dual NF

, Dual RO with chemical precipitation

, Dual RO with softening pretreat ment with high pH operation (High Efficiency RO (HERO TM )) , and Dual RO with Slurry Prec ipitation and R ecycling RO (SPARRO) . Other membrane hybrid processes include novel combinations of RO with other
established or novel membrane te chnologies. These include coupling FO with RO and coupling
RO with ED.

Dual RO with chemical precipitation

Dual RO with chem ical 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 trea tm ent of the concentrate from a primary RO system using a physical-chemical pro cess, followed by subse quent treatment in a secondary RO system. The chemical treatment step utilizes prec ipitation to remove calcium, magnesium, and other sparingly soluble salts, a nd is followed by filtration (e.g., media filtration or membrane filtration) for removing solids carryover from the preci pitation process. The secondary RO system is then operated at a highe r TDS, and requires higher pressures compared to the primary RO system. The combined recove ry of the process is reported to be 95% or greater for brackish water.

Figure 14. Dual RO with intermed iate chemical precipitation.

The positive attributes of this technology include the application of established unit processes and relatively low a dditional energy requirements. Negative attributes include additional chemicals, production of sludge from the chemical precip itation process, and footprint
and costs of chemical feed and storage facilities. This approach has recently been pilot test ed at the Metropolitan Water District of Southern California [77]. A dual RO configurati on 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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46 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 studi es 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 desi gn specifications are exceeded, and may require the use of NaOH, Na 4 EDTA, 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. Chemic al storage and sludge dewatering facilities will be required, in additio n 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 re quired for flow rates, chemical dosing, and RO element pressure. System may require substantial overs ight to ensure proper operation of the primary RO stage brine management systems. Level of flexibility: May have m oderate 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 re quire pH stabilization or remineralization. This may be achieved by lime bed contactin g or by blending small amounts of filtered and sterilized feedwater with permeate.RPSEA Project 07122-12
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47 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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48 Dual RO with softening pretrea tment and high pH operation (HERO TM : High Efficiency RO)
This patented technology [81] consists of a hardness an d alkalinity removal step, a degasification step to remove carbon dioxide, and intermediate cau stic addition to increase the pH of the RO feed water. This technology was devel oped to produce water of exceptionally high purity for the micro-el ectronics industry. For municipal brackish water, the process combines a tw o-phase RO process with chemical pretreatment of primary RO, intermed iate 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
pretreatm ent 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 rec overy rates of approximately 95%.

Figure 15. Schematic of a dual RO system that incorporates a soften ing pretreatment and intermediate high pH operation (High Efficiency RO (HERO TM )).

The HERO TM system has been utilized to enhan ce recovery of surf ace 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 SO 4 with the presence of other constituents including SiO 2 , B, Ca, Ba, Mg, and HCO 3 . Results demonstrated that recoveries of
95% to 98% were achie vable with the HERO TM system. A demonstration scale facility at the Arlington Valley Power Station in Arizona was constr ucted [83]. The facility is designed to treat 2.4 MGD of cooling tower blow down that contai ns 10,000 mg/L of TDS and is saturated with
SiO 2 . A summary of the technical assessment for a dua l RO with chemical precipitation is listed

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49 Table 19. Summary of technical assessment of dual RO with softening pretreatment and high pH operation (High Efficiency RO (HERO TM ))

Criteria Description/Rationale Status of technology Technology has undergone lab-scale t esting on surface water, and demonstration-scale testing on cooling wa ter 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 a pplication range is between 500 mg/L and 10,000 mg/L. Moderately high removals of m onovalent and divale nt 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 qua lity is dependent on feed water salinity and operating conditions. Lab-scale studi es 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/m 3 (0.48 to 0.80 kWh/bbl)

Chemical use Chemical cleaning rates de pend on feed water quality. Cleaning will typically occur after certain design specifications are exceeded, and may require the use of NaOH, Na 4 EDTA, or HCl. IX process will require regeneration with strong acid, likely H 2 SO 4 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. Chemic al storage and sludge dewatering facilities will be required, in additio n 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 require d 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 m oderate sensitivity to organic and inorganic constituents in the feed wa ter. 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 syst ems 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 co agulation and pre-filtrati on 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.RPSEA Project 07122-12
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50 Table 19. Summary of technical assessment of dual RO with softening pretreatment and high pH operation (High Efficiency RO (HERO TM ))

Criteria Description/Rationale Post treatment of product

water Product water will require pH stabilizat ion 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 re quired. Relatively high recovery rates exceeding 90% generate very minor amounts of concentrated brine. Sludge from the sedimentation basin w ill 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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51 Dual RO with SPARRO: Slurry Precipitation and Recycling RO
In SPARRO, specific crystals ar e added to feed water to aid in pr ecipitation 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 recy cling the seeded slurry were first patented in 1980 [84]. Seed crystals are added to the water in a tubular RO membrane sy stem and the scaling compounds are precipitated on the seed crystals in stead of on the membrane. The seed crystals serve as preferential growth sites for calcium sulf ate and other calcium salts and silicates, which begin to precipitate as their so lubility 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. B ecause 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 prefer ential precipitation systems [85]. A series of pilot tests were also performed by Resour ces Conservation Company (RCC) based on the original patented technology ([84, 85]. Subseque ntly, there have been other tests of the technology based on the c oncept of adding seed crystals to a tubular membrane configuration.
Two variations of the further te sting are discussed below. The fi rst approach is illustrated in Figure 16 [86].

Figure 16. Schematic of Seeded Slurry Precipitation and Recy cle 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 se ed crystals is processed in a cyclone separator to separate the crystals, and th e desired seed concentration is maintained in a reactor tank by controlling the ra te 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 te sted at pilot scale in South Africa, at the EastRPSEA Project 07122-12
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52 Rand Proprietary Mines [86]. A pilot testing of this approach for concentrate treatment tested at the Eastern Water Municipal Di strict in California [87]. Another variation of the seeded slurry appr oach 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 syst em [88]. The process was developed for an agricultural drainage water reclamation application and test ed at bench scale. The process, known as double pass, preferential preci pitation, reverse-osmosis process, or DP 3 RO TM , is proprietary and in the process of applying for patent. Although the TDS level in the agricultural dr ainage water is typically between 3,000 to 12,000 mg/L, the recovery of a conve ntional RO system treating th is 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 reco very of 92-96%. The first pass NF uses calcium sulfate seeds in a seeded slurry recycle config uration 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 technol ogy include increased RO recovery in an agricultural drainage water appl ication. Negative attrib utes include requirem ent of tubular NF membranes, larger footprint for tubular membra nes, a two-pass system (and associated energy and costs), and additional chemicals. This appr oach has been tested at bench-scale using drainage water from the Panache Drainage Di strict in California [ 88]. A summary of the technical assessment for a slurry precipitati on and recycling RO system is listed in Table 20.

Table 20. Summary of technical assessmen t 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 a pplication 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 additio n 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 desi gn specifications are exceeded, and may require the use of NaOH, Na 4 EDTA, or HCl. Life cycle No data is currently available.RPSEA Project 07122-12
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53 Table 20. Summary of technical assessment of slurry precipitation and recycling RO (SPARRO).

Criteria Description/Rationale

O&M considerations Monitoring and control re quired for flow rates, chemical dosing, and RO element pressure. System may require substantial overs ight to ensure proper operation of integrated system. Level of flexibility: May have m oderate 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 stabili zation or remineralization. This may be achieved by lime bed contactin g 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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54 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 sa lts 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 syst em. Impaired feed water contacts one side

of the forward osmosis. Water diffuses form th e feed solution into th e draw solution. An RO system is then employed to reconcentrate th e draw solution and produce pure water permeate.

Hybrid FO-RO systems have undergone pi lot-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 sy stem was completed at a landfil l in the Pacific-Northwest of the United States [76]. During full-scale test ing 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 os motic 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 barrie rs, in the form of two dense, non-porous membranes, which allows for the system to treat highly impaired water with high rejection of so lutes. The FO membrane will act to re ject most contaminates in the feed water, including scale forming minerals, mo st 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 wa ter recovery to an RO system of equivalent production capacity. FO-RO systems may be deployed in highly portabl e, trailer mounted membrane skids, and are highly modular. An FO-RO system requires a st able source of electrical energy to operate. System cleaning is highly dependant on feed wate r quality; however, the FO membrane in highly resistant to membrane fouling and scaling. Mechanical cleaning of FO membrane modules hasRPSEA Project 07122-12
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55 been shown to be a highly efficient method fo r restoring membrane performance without the need for chemicals [72]. However, chemical clea ning and the addition of s cale inhibitors may be required for both the FO and RO subsys tems depending on feed water quality. The service life of an FO-RO system is currently unknown, however RO membrane elements will likely require repl acement within 3 to 7 years of operation [36]. Industrial scale FO-RO systems would be highly automated syst ems, and would require relatively little supervisory oversight. The FO subsystem is capab le of treating highly variable feed water qualities and protects the RO me mbrane modules from harmful membrane foulants. The system would require few major maintenance periods; howeve r, the system would n eed 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 ge nerated 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 st ream. Additionally, th e FO draw solution may require infrequent disposal and addition of a new draw solution as sparingl y soluble solutes and other membrane foulants slowly accumulate in the draw solution reconcen tration loop [92]. A su mmary of the technical assessment for an FO-RO system is listed in Table 21.

Table 21. Summary of technical asse ssmen t 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 a pplication 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 desi gn specifications are exceeded, and may require the use of NaOH, Na 4 EDTA, or HCl. Life cycle No data is currently ava ilable for hybrid system; however, RO elements will likely require replacement between 3 and 7 years of operation.RPSEA Project 07122-12
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56 Table 21. Summary of technical asse ssment of hybrid FO-RO system.

Criteria Description/Rationale

O&M considerations Monitoring and control re quired for flow rates, chemical dosing, and RO element pressure. System may require substantial overs ight 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 stabili zation or remineralization. This may be achieved by lime bed contactin g 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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57 Dual NF
In this approach the co ncentrate 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 proj ects, 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 syst em, however the challenge water c ontains 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 syst em. 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 so luble salts that are near their saturation limit,
and would otherwise lead to seve re scaling of the secondary NF.

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58 Thermal Technologies

In distillatio n processes, ener gy is used to heat feed wate r that evaporates and then condenses to become purified water. Distillatio n 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 wa ter desalination; this is larg ely due to the higher energy requirements of conventional ther mal desalination processes. Th ermal separation processes are still employed in places where wa ste 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 evap orate more feed water. Some di stillation plants are hybrids of more than one desalination technology, such as MED-VCD [96]. The wa ste product from these processes is a solution with hi gh salt concentration. By using hybr id thermal technologies, zero liquid discharge can be achieved through brine concentrator and crystallizer. Membrane systems typically have advantag es over thermal processes. These include lower energy consumption, lower capital cost, a nd smaller physical footprint. However, feed water to membrane systems requires extensive pret reatment, and the processes are not applicable to very high salinity water (e.g., above seaw ater 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 attr active and competitive in certain applications, particularly for achieving zero liquid discharge and treating highly contaminated water. Besides distillation technologies, new therma l separation technologies such as freeze-thaw and dewvaporation have been developed fo r desalination of water.

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59 Multi stage flash
The multi stage flash (MSF) distillation process is based on the principle of flash evaporation in which water is evaporated by re ducing the pressure as opposed to raising the temperature with additional heat/energy. In MSF th e heated feed water fl ows into a stage with lower pressure and immediately boils or flash in to steam [94]. The high efficiency of the MSF process is achieved by preheati ng new feed water through capturi ng of the heat of condensation in each flash chamber or stage. A simplified schematic of an MSF seaw ater desalination plant is shown in Figure 18 . The
incom ing seawater passes through the heating stage(s) and is preheated in the heat recovery/condenser sections of each subseque nt stage. After passing through the last heat recovery section, and before entering the first stage, the feed water is furt her 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 high est temperature, after which it is passed th rough 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 th e superheated conditions associat ed with the temperature and pressure of each stage (each lower than th e 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 M SF process contains ty pically 2–10 mg/L TDS, and requires remineralization throug h post-treatment process [98][99]. The range of recoveries for conventional MSF desalti ng process is limited to approximately 10-20% for seawater [94].

Figure 18. Simplified schematic of MSF seaw ater desalination pl ant (Source: [97]).

According to the Global Water Intelligence (GWI) report, MSF had a market share of
more than 60% of the worldwide desalination ca pacity in 2003 and decr eased to 34% by the end of 2005 due to the competition of membrane technologies [38]. M SF can be applied to a wideRPSEA Project 07122-12
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60 range of feed water quality bins including produced water. MSF of ten requires centralized design
and construction of la rge-scale plants.
Formation of scale on heat tr ansfer surfaces is a major operating problem in thermal desalination processes. It impedes the rate of he at 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 polycar boxylic and polymaleic acids in conjunction with mechanical sponge ball cleaning to control alkali ne 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 tec hnical assessmen t of MSF.

Criteria Description/Rationale

Industrial status Mature and robust technology fo r 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 consid erations 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 aci d, EDTA, or other antiscaling
chemicals. Life cycle Typically 20 years, although mo st plants built in the 1970’s and 1980’s are still in operation with expected life of over 30 years.RPSEA Project 07122-12
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61 Table 22. Summary of tec hnical 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 fr om $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 contactin g 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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62 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 temp erature and then to deliver the additional energy needed for the heat of vaporization to transform a portion of the saline wate r 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. Typi cally, 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 f ilm to promote rapi d 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 dr ive 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 ex changers 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 co mbination 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 ol der 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 sy stems have been introduced to reduce the undesirable characteristics (e.g., low heat transfer rate and high rate s of scale formation) of theRPSEA Project 07122-12
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63 old MED submerged tube evaporators. Falling film evaporators such as vertical tube evaporator (VTE) and the horizontal tube ev aporator (HTE) of new MED plants have a number of distinct advantages [96]. They provide hi gher overall heat transfer coeffi cients and low specific heat transfer surface area compared to MSF desalinati on 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 pr ogress 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 co mmissioned in Layyah desalination plant in Sharjah (UAE) in 2001. It consists of two ME D 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 qua lity, including produced water. MED also offers the possibility of re ducing 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 techni cal assessmen t 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 TD S 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 sa tisfied and no major problems have been experienced [96].RPSEA Project 07122-12
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64 Table 23. Summary of techni cal 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 ope rate 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 membra ne 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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65 Vapor Compression Distillation
In vapor com pression 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 gene rated within the unit itself. The mechanical compressor is usually elect rically or diesel driven. Thermal compression uses high-pressure steam. Compression raises the pr essure 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 ev aporation chamber by a compressor and except for the first stage the vapor is co ndensed on the outsides of tubes in the same
chambers. The heat of condensation is used to ev aporate a film of saline water applied to the
insides of the tubes within th e 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 po wer 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 desalina tion as well as treating produced water and RO concentrate (i.e., brine concentrator applic ation) 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]).RPSEA Project 07122-12
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66 Table 24. Summary of tec hnical 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 approximate ly 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 crystalli zation 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 longe r 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 ope rate continuously, with shutdown only for planned maintenance once per year. Types of energy required: thermal and electricity.

Overall costs The capital costs depend on vari ous factors including size, materials of construction and site location. The operating costs depend on the purpose of plant; the costs to achieve ZLD are si gnificantly 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].RPSEA Project 07122-12
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67 Table 24. Summary of tec hnical assessment of VCD.

Criteria Description/Rationale Pre-and post treatment VC requires less rigorous pretreatment and feed conditioning as compared
to membrane treatment. Product wate r 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.

N ote: 1 barrel = 42 US gallons

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68 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 year s in desalination of seawater and brackish waters. More recently, hybrid ME D-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 th e 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 th ere 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 requiremen ts to recirculate larg e 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 capac ity 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 co nventional systems. A barge mounted MED-MVC hybrid was built in Germany and shipped to Sa udi 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 t echnical assessment of MED-VCD is listed in
Table 25

.

Table 25. Summary of techni cal assessmen t 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 a ll types of water chemistry makeup.

Product water quality Product water quality for ME D-VCD plants is typically very high. Production efficiency (recovery) Product water recovery is between 30% a nd 45% for seawater desalination. GE brine concentrator and crystallizer can in crease 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 acco mmodate the large plant footprint. The availability of low-pressure steam, e ither 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 cons umption 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].RPSEA Project 07122-12
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69 Table 25. Summary of techni cal 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 high ly 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 opera te 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 a pproximately $6/gpd ($250 per bbl per day) [98]. The costs may vary depending on various factors including size, materials of construction and site location. Opera ting 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 lim e 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 wate r 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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70 Freeze/Thaw Evaporation (FTE ® )
The freeze/thaw evaporation is a water treatment process that combines freezing and thawing cycle with conventiona l evaporation technology [104]. A schematic diagram of FTE ® is
shown in Figure 21 . When the ambient air temperature is b elow 32 °F (0 °C), the saline water (feed water) is sprayed or dripped onto a freezi ng pad to create an ice pile. Relatively pure ice crystals form and an unfrozen solution (brine) containing elev ated 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 r ecycling. When the temperatures rise, the ice melts and the runoff from the freezing pad is highly purif ied water that can be diverted to a treated water storage facility for beneficial uses or surface discharge. During warm months, the FTE system is opera ted 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 dispos al 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 Am oco Production Company, McMurry Oil Company, Crystal Solutions, and Gas Resear ch Institute. Results from these field tests confirm both the process economic viability and its potential to produce usable, quality trea ted water from oil and natural gas produced water. As of 2003, two FTE pl ants continued to operate commercially in Wyoming: one in the Jonah gas fi eld south of Pinedale and the other in the Re d Desert near Wamsutter ( Figure 22 ). The treatment capacity of those pl ants is m ore than 40,000 gallons a day (950 bbl/day) [105].RPSEA Project 07122-12
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71 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) (1999-200 3) and is now owned by Samson Resources Company and operated by CS. The initial nomin al 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 cap able of treating a broad variety of wastewater, a nd of removing over 90% of produ ced water constituents [104], including total suspended solids (TSS), total diss olve solids (TDS), tota l recoverable petroleum hydrocarbons (TRPH), volatile organic compounds (VOC), semi-volatile organic compounds, and heavy metals. However, the FTE ® process is not capable of tr eating wastewater having more
than 5% methanol. The FTE ® operation performance during wintertime is shown in Table 26 . A
technical assessm ent 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 tec hnical 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 qua lity 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.

P roduction efficiency (recovery) P roduct water recovery is approximately 50% during wintertime. No water can be recovered during other seasons as the process works as a conventional evaporation pond.RPSEA Project 07122-12
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72 Table 27. Summary of tec hnical 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 hydr o-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 adap t to highly varyi ng 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 produc t 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. Curren tly, 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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73 Dewvaporation – AltelaRain SM Process
Dewvaporation is a process that involves hum idification-dehumidification desalination. It reduces the energy costs by usin g counter-current heat exch ange 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-gr ade heat from various
resources. The tower unit is built of thin plastic films to a void corrosion and to minimize equipment costs. Towers are relatively inexpensive because they operate at atmospheric pressure. Altela, Inc. has designed, manufactur ed, and tested several AltelaRain SM prototype systems based on the dewvaporation process. A schematic of the AltelaRain SM process is shown

in Figure 23 . Three full-scale AltelaRain SM ARS-4000 systems have been deployed at natural gas wells in the San Juan Basin near Farmingt on, NM [106]. The ARS-4 000 system can process approximately 4,000 gallons per day (100 bbl/day) of produced water with sa lt concentrations in excess of 60,000 mg/LTDS.

F igure 23. Schematic of AltelaRain TM process (Source: [107]).

AltelaRain SM System can reduce effluent disposal volumes by as much as 90%. Because the treated water stream is distilled water, the AltelaRain SM produces very high quality water. In one test the TDS concentration of produced wa ter 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 AltelaRain SM treatment [108].
The AltelaRain SM technology requires no special infras tructure, supplies, or consumables for its unattended operation. It requires only regula r 110V electricity (from either a generator or solar panels), making it a water treatment alterna tive 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 h eat or waste gas is not readily available, steam can be generated using a small natural gas-fired bo iler. Altela currently operates three systems inRPSEA Project 07122-12
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74 such remote locations that both the electricity an d heating needs are satisfi ed 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 co st would be $20.85 per 1,000 gallons.

If waste heat or solar heat were availabl e, the operating cost would reduce to the electrical cost of pumps and fans [109].

A technical assessment of the AltelaRain SM process is summarized in Table 28.

Table 28. Summary of technica l assessmen t of AltelaRain SM 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 el ectricity 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/evapora tion 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 adap t to highly varyi ng 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 reporte d the cost structure asso ciated with building, installing, maintaining, and servicing th e system is lower than the escalating costs associated with traditional produced water hauling and reinjection.RPSEA Project 07122-12
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75 Table 28. Summary of technica l assessment of AltelaRain SM 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 becau se 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 transpor ted 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 applicati on. 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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76 Alternative Technologies

Ion exchange process
In ion exchange (IX), removal of specific ions or com pounds fr om a stream is facilitated by the exchange of a pre-saturate d 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 proces s and is commonly applied to drinking water treatment for hardness removal, but is in creasingly being studied for the removal of radionuclides and nitrates [110, 112]. IX resins are typically compos ed of synthetic resins or ac tivated alumina. These resins
are characterized as either str ong 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

 SO 3 H )  Ca 2   ( R

 SO 3 ) 2 Ca  2 H  (strong acid resin)

2( R

 COOH )  Ca 2   2 HCO 3   ( R

 COO ) 2 Ca  H 2 O  CO 2 (weak acid resin)

( R

 N H 3 O H )  HCl  ( R

 N H 3 Cl )  H 2 O (basic resin)

IX resins are typically manufactured to have readily reversible reactions, which allows for the IX resin to be regenerated once its ad sorptive capacity is exhausted. The IX resin’s adsorptive capacity is exhausted when the ta rget ion reaches a prescribed breakthrough concentration in the IX product water. To ach ieve high purity water quality, many conventional IX processes are operated with mixed beds to achieve removal of bot h 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 be tween 300 to 300,000 bed volumes (BV) before requiring regeneration, de pending 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 fluidi zed, packed bed configurations. IX is an established water treatment technology that is u tilized 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 processe s includes packed resin beds (sometimes referred to as columns) and onsite regenerant and cleaning chemical storage. The type of regenerant chemicals de pends on the characteristics of the IX resin employed and may be
include solution of H 2 SO 4 , HCl, NaOH, Na 2 CO 3 , or NaCl. Typically, IX processes operate with mi nimal energy demand and may require only electricity for pumping fluids under low hydr aulic pressure. Operation and management
considerations for IX include occasional disinfection of IX resin with NaOCl or H 2 O 2 . Careful management of the feed stream is also necessary to ensure that fouling agents such as suspendedRPSEA Project 07122-12
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77 solids, scale forming materials (e.g., CaSO 4 ), and oxidized metal are not present in the feed water. Additionally, many IX resins are sensitiv e to free chlorine oxidation. IX processes must also be carefully managed to reduce osmotic shoc k and mechanical abrasion of IX resin, which will lead to physical lo ss of the resin [114]. Operating costs for standard IX processes vary greatly with feed water quality and loading rate. An economic feas ibility analys is conducted by DowEX (Dow Chemical Company, Midland, MI) estimated that IX, after a conventional pretr eatment (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 significan t contributions. At 880 gpm, operating costs increase to ~80% [115]. Waste disposal needs of IX processes include the need to neutrali ze and dispose of spent IX regenerant solution. These so lutions typically repres ent a very low volume of wastewater, but may be highly saline and require additional treatme nt to limit disposal co sts. 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 app lication 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 a nd 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 pro cess has a highly variable ope rational 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, howev er 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 l east 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

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78 Table 29. Summary of technical assessment of IX processes.

Criteria Description/Rationale

Chemicals Chemical cleaning rates depe nd 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, H 2 SO 4 , NaOH, Na 2 CO 3 , or NaCl. Additional chemical disinfection may be required to mitigate biofouling and will typically consist of H 2 O 2 or NaOCl cleaning
solutions. Life cycle The average lifespan for anion ex change 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 mode rate flexibility depending on resin
type. Level of robustness: IX processes are highly sensitive to fouling from organic materials and suspended solid s. 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 rege neration 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 stabili zation or remineralization. This may be achieved by lime bed contactin g 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 exc eeding 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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79 Capacitive deionization (CDI) & El ectronic Water Purifier (EWP)
Capacitive deionization (CDI) is an emer ging desalination techno logy. The Lawrence Livermore National Laboratory (LLNL) started st udying 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 th e 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, an d sodium, and the positive electrodes attract negatively charged ions such as ch loride, nitrate, and silica. The major mechanisms related to the removal of charged constituents during water treatment are physisorption, chemisorption, electrodeposition, and/or electrophoresis. Unlik e ion exchange, no additional chemicals are required for regeneration of the el ectrosorbent in this process. Adsorbed ions are desorbed from the surface of the electrodes by eliminating the elect ric field, resulting in the regeneration of the electrodes. The efficiency of CDI strongly depe nds on the surface property of electrodes such as
their surface area and adsorption properties [116]. There are a variety of electrode material s and configurations to enhance the CDI performance. The LLNL developed and optimi zed 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) cartri dge [118]. Atlas developed the Electronic Water Purifier (EWP ), which is a hybrid CDI and electrodeionization (CDI-EDI) technology using activated carbon electrodes that ha s a coating and a cond uctive material [119].

++++++++++++++++

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

### Positive electrode

Negative electrode Salty

water Pure

water DC

power supply

Neutral electrode

Neutral electrode Regeneration

water Concentrate

Figure 24. Schematic of Cap acitive 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 pilo t-scale testing of produced water treatment at a sandstone gas production field in Montana using two industr ial capacitive deionization technology (CDT TM ) aquacells developed by CDT, Inc., Dallas, TX. For the development ofRPSEA Project 07122-12
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80 cost-effective CDI system, the capacitance of carbon aerogel have to be improved while production cost should be reduc ed. Long regeneration time and carry-over of ions following regeneration limit the efficiency of treatment of highly saline water a nd decrease the production recovery [116]. The laboratory and field-testin g during treatment of sandstone produced water
indicated that CDI exhibited mu ch less fouling/scaling propens ity 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’ (W xLxH) 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 technolo gy is summ arized 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 P ilot Test--250 BPD (Source: [119]).RPSEA Project 07122-12
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81 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 wa ter 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 wate r 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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82 Gas Hydrates
Gas hydrates are crystalline water-based soli ds that physically resemble ice. However, instead of the closed crystalline lattice structur e of ice, gas hydrates have open lattice structure with a cavity that traps non-polar molecules (typ ically gases). A photograph of a gas hydrate is
shown in Figure 26 . The hydrogen bonded water molecules esse ntially f orm a cage structure that traps gases including CH 3 , H 2 S, and CO 2 . 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 sedi ments [121]. The formation and subsequent processing of gas hydrates produ ce three streams: a pure wate r stream, natural gas, and
concentrated brine.

Figure 26: The physical and chemi cal 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’ insi de (right) (Source: [123]).

A collaborative research initiative conducte d by BC Technologies in conjunction with Oak Ridge National Laboratory (O RNL) and the International Petroleum and Environmental
Consortium seeks to evaluate the effectiveness of forming gas hydr ates 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 perfor med 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 c ould recover 50-60% of th e hydrates in a single pass; yet, of the hydrates recove red, only 23-29% of the feed wate r 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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83 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 othe r 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 groundwa ter [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 pl ace or removed and hauled offsite for disposal. This disposal method can be expensive due to the la rge surface area required and the associated land and impermeable liner costs [ 125]. Regulatory requirements, eco logical impacts, and possible
concentration of trace elements to toxic leve ls 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 cu rrently 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 evaporati on basins. Examples of commercial evaporation
facilities can be found in Colorado, New Mexico, Utah, and Wyoming [1]. Solar energy ponds are special type of eva poration 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 th e concentrate in the p ond. The solar energy penetrates the upper, less concentrated layers. Th e 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 trappe d in this layer is extracted and can be used to generate electricity. Solar ponds have some concentrat e 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]. Fo r example, the Powder River Basin (PRB) of Montana and Wyoming and the Sa n 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 Louisi ana 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 consid erable 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 netti ng helps to avoid this problem [57]. The technical assessment of eva poration ponds for produced water disposal is
summarized in Table 32

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84 Table 32. Summary of technical as sessment 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 variab le 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 requi re 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 wa ter, more economical and competitive
to small flows. Note: 1 barrel = 42 US gallons

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85 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 ov er vertical transport surfaces to reduce the pond footprint. The hydrophilized evapor ation surfaces can consist of woven nettings, or non-woven geo-textiles, or tuff (vocanic ro ck) arranged in tray s. Studies indicate that the WAIV method intensifies the evaporation proce ss to about 10 times that of re gular evaporation ponds [127]. The footprint of the WAIV ponds can be much smalle r 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 sim ilar conditions of low humidity and high temperatur es in CBM development areas. The US Bureau
of Reclamation tested th is technology and identified that th e dripping nozzles would salt up and clog. This required cleaning of th e nozzles on a regular basis [126].
Lesico CleanTech manufactur es the WAIV evaporation t echnology [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]).RPSEA Project 07122-12
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86 Table 33. Summary of technical assessm ent 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 requirement s 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 pum ping 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 requi re 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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87 Commercial Thermal Processes

GE: Evaporative produced water treatment an d steam generation using MVC evaporators
Steam injection is becoming a common meth od 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 concentra tion in de-oiled produced water ( Figure 28 ). The hardness
and iron are further removed th roug h a weak acid cation (WAC) IX process to ensure the sound operation of the steam generato r. 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 flui dize the heavy oil [129]. In mo st 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 so lid 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) met hod 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 al ternative to traditional produced water treatment and steam generation system, GE developed an evapor ative produced water treatment process using mechanical vapor compression ( MVC ) evaporators for supplying high quality steams to SAGD. The heat transfer coe fficient for the vertical-tube, falling-film MVC evaporators is higher than for traditional evaporators, offering improved evaporation efficiency and energy savings. This arrangement, in conj unction with a propriet ary 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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88 Figure 29. A schematic of a vertical-tube, fa lling-film MVC evaporator (Source: [129]).

F igure 30. The vertical-tube, falling-film MVC evaporation system for produced water treatment and steam production (Source: [129]).

D e-oiled produced water enters a feed tank wher e the pH is adjusted. The wastewater is pumped to a heat exchanger that raises its temp erature 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 br ine flows down the tubes, a small portion evaporates and the rest falls in to the sump to be recirculated ( Figure 29 ). The vapor
travels dow n 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, wher e its latent heat is given up to the co oler brine slurry falling inside. As the vapor loses heat, it condenses as distilled wa ter. The distillate is pumped back through the heat exchanger, where it gives up sensible heat to the incoming wastew ater. A small amount of the brine slurry is c ontinuously blowdown from the evaporator to control density [129].RPSEA Project 07122-12
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89 T he OTSG or drum boiler blowdown can be recy cled to the evaporator feed, eliminating the need to dispose of this waste stream w ithout affecting recovered water quality. The evaporator blowdown is disposed via deep well in jection or treated further by a crystallizer to eliminate all liquid waste. The crystallizer produc es a dry cake material for disposal ([129]).

E vaporative produced water treatment was test ed in 1999, and was initially used by Japan
Canada Oilsands and PetroC anada, respectively. The blowdown from the OTSG steam separators was effectively pro cessed by an evaporator and crys tallizer combination in a ZLD system. Today, there are about 16 produced wate r evaporators operating or under construction in nine plants in Alberta, Canada and other regions ([129]).

A s 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 trea tment systems (WLS or HLS, WAC, etc.)

 Minimizes softener sludge and othe r 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 th e high energy-consumption and economical scale of treatment plant, the thermal technologies ar e more competitive for high TDS water and centralized treatment systems. The technical assessment of th e 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 approxi mately 98%. 2% blowdown can be disposed via deep well injection or treated by a crystallizer to ZLD.

Infrastructure
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90 Table 34. Summary of technical assessment of GE – evaporative produced water treatment using MVC evaporators.

Criteria Description/Rationale Energy consumption The power consumpti on of MVC evaporator is 70 kWh/kgal of distillate produced (2.94 kWh/bbl) [129]. A typical produced water evaporator will consume 60-65 kW h/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 varyin g 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 produ ced 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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91 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 variou s water and wastewater treatment technologies
under the WATER TRAK TM 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 reus e 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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92 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 Gr anbury-based Fountain Quail Water Management. This MVR evaporation NOMAD system is an ener gy efficient process that uses a very compact welded cassette heat exchanger with a plate- and-frame construction an d a rising-film design. With this design, boiling occurs on a wet surf ace, minimizing scale de position that occurs in conventional thermal technologies. For frac flowback water treatment, feedwater is first dosed with flocculants to coagulate/flocculate the suspended solids and or ganic matters. The wastew ater 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 ev aporator unit to remove dissolved solids ( Figure

31 ). A compressor is used to add the energy re quir ed to boil water. The feed water passes through two preheat exchangers where heat is ab sorbed from the distillate and concentrate products leaving the system. The feed then pass es into a recirculati on loop where concentrate circulates through an evaporator exchanger an d a vapor / liquid separator. A portion of the
concentrate is boiled to steam in the evaporator exchanger and se parated from the liquid in the separator vessel.
The manufacturer claims that the MVR ev aporation can recycle up to 85% of frac
flowback water into distilled water. With a lo wer contamination level in the feed water, the system could achieve a 90% to 95% recovery of di stilled water [131]. The tr eated water is stored
in tanks for future reuse. The system is skid mounted. The footprin t 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 f eet long, weighing 25,000 pounds. • An evaporator module 37 f eet long, weighing 42,000 pounds. • A compressor module 30 feet long, weighing 96,000 pounds.

The system also includes interconnecting pi pes and electrical conn ections, and a 50-kW generator. It needs no external source of electri c power. It draws natural gas directly from the well to run the compressor and to drive the gene rator, which produces el ectricity to power the pumps, instruments, and controls. Figure 32 shows a close view of the Aqua-Pure unit operating by Devon Energy Corpo ration near Decatur, Texas. A summary of the technical assessment of Aqua-Pure MVR Evaporation process based on the information provided in the ma nufacturer’s website is listed in Table 35

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93 Figure 31. Schematic of the Aqua-Pur e MVR Evaporator (Source: [131]).

Figure 32. Closer view of the Aqua-Pure unit (S ource: 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 qua lity 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).RPSEA Project 07122-12
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94 Table 35. Summary of technical assessment of Aqua-Pure MVR Evaporation process.

Criteria Description/Rationale

Infrastructure
considerations No special infrastructural requireme nt 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 shoul d 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 constructi on, that is, alloys with high corrosion resistance [93].

O&M considerations Low level of monitoring and c ontrol required for feed pH, flow rates as well as steam and vessel pressures. High level of skilled labor require d to operate MVR evaporators. High level of flexibility: easy to adap t to highly varyi ng 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 subs tances 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 th e 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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95 212 Resources - Mechanical Vapor Recompression (MVR) Evaporation

S imilar to Aqua-Pure MVR evaporation pr ocess, 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 velo city flash evaporation to recover brine
and distilled water

 Steam distillation integrated with the evapor ator 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 pa tented VACOM technology ( http://www.vacomllc.com/ ) that combines mechanical vapor reco mpression with turbulent flow h eat exchange technology. The Vacom vapor compression, flash evaporation syst em is applicable for high TSD waters from deep-well, hydraulic fracing, na tural gas wells, deep coalbed methane wells, and other oil and gas produced waters. 212 Resources’ system is able to recover oil, meth anol, total dissolved solids, minerals, and metals from water that are associated with dr illing and production. 212 Resources has a contract to build a larg e plant in Wyoming for treatment of frac flowback water and produced water from natura l gas fields [134]. In May 2008, 212 Resources announced that the company had signed a cont ract 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 th e 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 di fferent 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 r ecycling 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’ proce ss is listed in Table 36

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96 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 requireme nt as the unit is skid-mounted. The footprint of pods is 40’x60’. Re quire 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 constructi on, 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 require d to operate MVR evaporators. High level of flexibility: easy to adap t to highly varyi ng water quality and quantity. High level of robustness: high ability of the equipment to withstand harsh
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97 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 isassumed 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 settli ng and filtration to rem ove suspended solids and organic matter.
Product water includes UV and carbon filtration to remove miscible hydrocarbons. Remineralization or bl ending 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 th e 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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98 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 av ailable [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 ro tating disk. Superheated vapor in the cavity of a disk condenses on the inside surface. A slight te mperature difference across this disk allows heat to flow from the condensing liqui d to the evaporating fluid, driv ing 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 evapor ate more feed water [138]. A schematic for a five-effect WFRD unit operating in the va por compression mode is illustrated in Figure 34

.

Figure 34. Schematic flow diagram for a five -effect WFRD unit opera ting 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 de signed to improve heat transfer efficiency and reduce scaling and fouling [138]. Resistance to heat flow in di stillation is dete rmined by the thickness of the liquid layer on the evaporation and condensatio n surfaces. The WFRD design minimizes this thickness; resulti ng in very thin condensate and f eed 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 us ing CBM production water collected from two sources – the Powder River Basin (North east Wyoming / Southeast Montana, with TDS 1,068 mg/L) and the San Juan Basin (New Mexi co, with TDS 23,000 mg/L). Produced water from each source was treated using a prototype WFRD test unit; a single e ffect 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 pr oduced water with r ecovery rate of 90% . The AGV technology
removed 99% of the TDS from bot h raw produced waters without a ny 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 re duction for some inorganic constituents and TOCRPSEA Project 07122-12
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99 resulting from WFRD processing was less in the Po wder River samples, the levels measured in Powder River recovered water were very low [138]. Currently, AGV Technologies, Inc. is deve loping the PW-600 – the first commercial AGV product. It will be available for installati on in oil and gas produc tion and produced water disposal facilities. The PW-600 system is desi gned to process 25 kgal (600 barrels) of produced water per day. Initial PW-600 units are electr ically 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 demonstrat e 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 “I mproving Produced Water Quality for Coal Bed Methane. Prepared by AGV Technologies, Inc. for RPSEA” [138].

Table 37. Summary of technical assessmen t 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 re jection 70- 86%; ammonia rejection low. Production efficiency (recovery) Product water recovery is approximately 90%.

Infrastructure
considerations No special infrastructural requireme nt 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 i nhibitor 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 a nd control required for feed pH, flow rates as well as steam and vessel pressures. High level of skilled labor require d to operate distillation system. High level of flexibility: easy to adap t to highly varyi ng 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.RPSEA Project 07122-12
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100 Table 37. Summary of technical assessmen t of the WFRD distillation system.

Criteria Description/Rationale Pre-and post treatment Pre-treatment might incl udes settling and filtration to remove suspended solids and organic matter.
Product water includes UV and carbon fi ltration to remove miscible hydrocarbons. Remineralization or bl ending 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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101 Intevras Technologies, LLC: Evaporative Re duction and Solidification (EVRAS) units
Intevras Technologies , LLC, a Texas privately held company, has developed a thermal method for brine treatment called EVRAS (Eva porative Reduction and Solidification). The EVRASTM system is a patented technology that ut ilizes low-grade waste heat to concentrate and/or crystallize large vol ume 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 "crystal lizers" allow total evaporation, resulting in precipitated solids. The solid waste residue is th en removed for disposal, re-cycling, or resale (salts) in other markets. The EVRAS system overcomes the scaling pr oblems on heat exchangers through the use of (i) flexible films as the surface media for the ai r and brine contacting pro cess, and (ii) two step heat transfer process employing an intermediary heat transfer liquid. A schematic of the EVRAS process is illustrated in Figure 35

.

F igure 35. Schematic of EVRAS process for brine treatment (Source: [139]).

T he 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 wa ter can be evaporated out of 126 kgal (3,000 barrels) of concentrat ed saltwater, resulting in smalle r volume to be injected [140].RPSEA Project 07122-12
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102 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 mi nimal scaling problems

 Simplicity in operation and minimal maintena nce: operating at atmospheric pressure

 No blow-down or discharge

The EVRAS process is an evaporative syst em 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 inte nsive 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 su itable to treat large volume of waste streams and it may not be feasib le to treat point source of CBM produced water with varying flow rates. Th e 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 eva porate a portion of produced water from natural gas drilling in Barnett Shale [140].

Table 38. Summary of technical assessmen t 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 sens itive 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.RPSEA Project 07122-12
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103 Table 38. Summary of technical assessmen t 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 o F 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 ad apt to highly vary ing 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 so lids 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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104 Total Separation Solutions: SPR – Pyros
Total Separation Solutions , LLC (TSS) developed a new PYROS TM system for heating and evaporation of produced water. Fluid is pumped into the PYROS TM system, heated to evaporation temperatures, and concentrated. The byproduct of the process is clean steam that is condensed into fresh water by heating the in coming fluid. A methodology the TSS proposed for produced water treatment is shown in Figure 37

. The PYROS TM system includes cross-flow filtration modules to remove suspended solids from produced water and frac flowback waters. Cr oss-flow filtration using sintered metal tubes allows the continuous operation wi thout replacing filters. The PRROS TM is part of a modular system. TSS, LLC claims that the complete PYROS TM 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 ex cessive trucking costs [142]. The core technology of the PYROS TM system is ShockWave Power TM reactor (SPRTM).
Fluid is delivered into a SPRTM r eactor, where it is passed over the generator's spinning cylinder. The specific geometry of the holes in the cy linder, 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 ultrasoni c 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 diffe rence between metal and liquid, results in scale-free heating.

Figure 37. Schematic of PYROS syst em for produced water treatment ( Source : [142]).

TSS technology has been used to process m ore than 10,000 bbl of frac water per day for an operator in the Haynesville Shal e. The assessment summarized in Table 39 is based on the
inform ation provided on the website of TSS

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105 Table 39. Summary of technical assessmen t 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 hi ghly 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 ad apt to highly vary ing water quality.

Overall costs Not available. Pre-and post treatment Pre-treatment might include chemical precipitation, settling, and filtration to remove iron and manganese, suspe nded 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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106 Commercial IX Processes

EMIT: Higgins Loop
EMIT Higgins Loop technology is the most widely utilized IX process for CBM produced water treatment. EMIT currently ha s 18 operating treatment units in Wyoming, Montana, and Colorado. 17 of the operating treat ment units are located in the Powder River Basin, while one system is located in the southe rn most area of the Greater Green River Basin [143]. These treatment units have a reporte d treatment capacity of 336,000 to 1,176,000 gpd (8,000-28,000 bpd) [144]. The Higgins Loop operates as a continuous co untercurrent ion exchange contactor for liquid phase separations of i onic components, primarily sodi um. The unique aspect of the Higgins Loop is that it performs resin rege neration continuously during the process, with minimal need for system downtime during regenerati on. The IX contactor c onsists of a vertical cylindrical loop that contains a packed bed of resin separate d into four operating zones by butterfly or "loop" valves. These operating zones are illustrated in Figure 38 , and include pulsing (‘A’), reg eneration (‘B’), adsorption (‘C’), and back washing 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 exchan ge 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 str ong 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, re sin saturated with sodium is regenerated with a
4.11 M HCl solution (representing 1-10% of the treate d 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 becomesRPSEA Project 07122-12
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107 loaded with sodium, the flows to the Higgins Loop are momentarily interrupted. This allows advancement of the resin bed (pulsing) through th e loop in the opposite direction of liquid flow. Liquid flows are restarted after re sin pulsing is complete [143, 144]. Higgins Loop technology is best suited for feed water containing 3,500 mg/L TDS and dominated by NaHCO 3 [143]. Emit Higgins Loop model 3012 is built on two skids with a total footprint of 220 ft 2 , while the more popular model 6024 sh ips on three skids and has a total footprint of 450 ft 2 [145].System setup requires a large crane (shown in Figure 39 ), but is
otherwise re latively mobile.

Figure 39. Installation of EMIT Higgins Loop system in the Powder River Basin (Source: [145]).

Electric power consumption is esti mated between 4.96 to 12.4 kWh/kgal (0.21 to 0.52 kWh/bbl) [144]. Public data conc erning operational costs is unavail able at this time, however this costs will likely be similar to conve ntional IX processe s as described in Table 29 . System life cycle an d IX resin life are also not reported, however EMIT claims that the system is able to operate with greater than 98% r untime [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 technica l assessment for the EMIT Higgins Loop IX process is shown in Table 40

.

Table 40. Summary of technical assessmen t 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 NaHCO 3 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% rejec tion of Na is achievable, with additional removal of Mg, Ba, and HCO 3

. Production efficiency (recovery) Product water recovery is dependent on IX resin regeneration needs, but recovery typically exceeds 99%.RPSEA Project 07122-12
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108 Table 40. Summary of technical assessmen t of EMIT Higgins Loop IX process.

Criteria Description/Rationale

Infrastructure considerations This treatment pr ocess has operational footprint that varies from 220

ft 2 to 450 ft 2

. 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 depe nd 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 H 2 O 2 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 solid s. 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. Opera tions 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 stabili zation or remineralization. This may be achieved by lime bed contactin g 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 exc eeding 99% generate very minor
amounts of concentrated brine. Applicability for produced

water treatment Excellent – Treatment well suited fo r specific feed water constituents (primarily NaHCO 3 ), 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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109 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 monoval ent cations, especially sodium for SAR reduction, and is designed as a three-phase, conti nuous fluidized bed system. Though it is not recorded explicitly, it is likely that the Drake system utilizes a str ong 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 re generating (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 pro cess. Schematic taken from US patent [146].

The Drake system is in its third stage of p ilot 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, th e process may be capable of treating water with marginally higher salinity. Recent pilot tes ting results indicate a sodium removal of 93%. System recovery is reported to be greater than 97% [147]. System reject is composed of highly
concentrated Na 2 SO 4 , which may be dried and further c oncentrated in evaporation ponds to produce a commercial grade Na 2 SO 4

. A Drake IX system is estima ted to require two acres of su rface area, whic h includes a one

acre Na 2 SO 4 collection impoundment [144]. Th e 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 alsoRPSEA Project 07122-12
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110 requires two 16,800 gal (400 bbl) water tanks and a 4,400 gal (105 bbl) H 2 SO 4 regenerant tank [147]. Pre-treatment technologies may be required to remove resi n foulants from the raw water supply. Energy requirements are not explicitly stated, but are likely to be sli ghtly less than that required for the EMIT Higgins Loop system. Additional operation and management considerations may be inferred from the overa ll operation of IX pr ocesses. A technical assessment for the Drake IX process is summarized in Table 41

.

Table 41. Summary of technical asse ssment 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 NaHCO 3

. Product water quality Treatment process permeate quality is dependent on feed water salinity and operating conditions. 93% rejec tion of Na ions is reported. Production efficiency (recovery) Product water recovery is dependent on feed water quality and IX resin regeneration needs, but recovery w ith 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 ft 2 ). Individual systems may be highly mobile, however further construction may be necessary to provide increased protection from
the elements. Energy consumption Energy requirements are mi nimal 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 depe nd on feed water quality and IX resin adsorptive capacity. H 2 SO 4 regenerant is required to restore the IX resin’s adsorptive capacity. Additional chemical disinfection may be required to mitigate biofouling a nd will typically consist of H 2 O 2 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 di valent cations and metals. Level of robustness: IX processes are highly sensitive to fouling from organic materials and suspended solid s. 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 informa tion is provided on system up time. Types of energy required: electrical.

Overall costs No data provided.RPSEA Project 07122-12
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111 Table 41. Summary of technical asse ssment 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 requi re 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 exc eeding 97% generate very minor
amounts of concentrated brine. The concentrated Na 2 SO 4 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 NaHCO 3 . 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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112 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 footpr int, faster regeneration, and increased throughput compared to
conventional IX processes. The compressed bed system s are an extensi on 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 cat ion removal, and a sec ond system with three separate compressed-bed columns that contain a primary cation bed and anion bed followed by a polishing cation bed. The ion exch ange 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 th e two cylindrical beds pictured,
one is loaded with cation excha nge resin and the other with ani on exchange resin. Each column
houses 3 to 6 inches of ion exchange resin [148].

Eco-Tec Recoflo ® systems have been employed to treat copper electro lyte solutions, recover nickel salts, recover me tals from process solutions, and purify alternative fuels [150]. Recently, Eco-Tec was awarded a se rvice contract for a Marathon installation in the Powder River Basin (WY) [151]. The syst em 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 proce ss [149]. The system requires both H 2 SO 4 and NaOH to regenerate the cation and anion IX resins, respectively. Recoflo ® compressed beds are more
mobile than conventiona l IX processes and the Higgins Loop . A schematic of a full treatment train with two, skid-mounted three-bed systems operating in pa rallel 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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113 Figure 42. System schematic with two three-bed Eco-Tec Recoflo ® process operatin g 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% re jection of Na, Mg, Ca, and SO 4 ions is expected, in addition to significant metals removal. Production efficiency (recovery) No data is provided regarding ov erall process production efficiency.

Infrastructure considerations Eco-Tec’s Recoflo ® system is designed to utilize a smaller operational footprint that conventional IX pro cesses, 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 mi nimal 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.RPSEA Project 07122-12
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114 Table 42. Summary of technical assessment of the Eco-Tec Recoflo® compressed-bed IX

process. Criteria Description/Rationale

Chemicals Chemical cleaning rates depe nd on feed water quality and IX resin adsorptive capacity. H 2 SO 4 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 H 2 O 2 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 th e 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 solid s. 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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115 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 th at was designed to mini mize waste during resin regeneration (wasting only 25-50% for each rege neration cycle) and rins e water according to manufacturer information [152]. The Catalyx system was designe d for the removal of sodium (by ion exchange) and bicarbona te (through off gassing of CO 2 ), with the ion exchange chemical
reaction:

Na   HCO 3   R

H   R

Na   H 2 O  CO 2 

Waste minimization is facilitated by the use of three tanks that are responsible for shuffling regenerant and rinse wa ters of various qualities duri ng IX resin regeneration cycles. During the onset of a regeneration cycle, acidi c regenerant utilized from the previous regeneration cycle is first pr ocessed through the packed bed of resin in a counter-current
direction and wasted. A second tank containing acidified rins e water from the previous regeneration cycle is then pro cessed through the packed bed and r ecollected 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 th e IX bed it is co llected in the second tank. The third tank is refilled with pr oduct 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 limitati ons of this technology.

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116 Commercial Membrane Processes

CDM Produced Water Technology
CDM has developed a process fo r treating produced water c ontaining 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 tig ht 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 incl uded in the treatment train are dictated by the feed wate r quality and the desired produc t water quality. Some of the technologies that may be u tilized 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 anox ic 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 comput er program was devel oped 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 w eak acid cation (WAC) IX softener is used to
reduce hardness and other metals. The resin is re generated 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 comb ined with the product streams from the membrane processes and disc harged, depending on the scenario and the feed water quality. After pretreatment, low-pressure reverse osmo sis (capable of achievi ng 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 c oncentrate stream to stab ilize 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 th at 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 eith er 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 tr eatment for the water to be put to beneficial use. In these cases, a limest one bed is used to add calcium to the water and
lower the SAR. Some produced water applications may requi re ZLD because brine disposal is not feasible or is too expensive. For ZLD applicatio ns, 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 w ith the RO permeate streams for discharge or for
other beneficial uses. The residuals from the ev aporator can be either concentrated brine or solids. Depending on feed water quality and discharge permits, filter backwash stream and WACRPSEA Project 07122-12
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117 regeneration brine can be blended with the prod uct water streams (low a nd 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 produc ed 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 cont ained 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 test ing experience in the Powder River Basin: $0.14/bbl or $3.33/1000 gal (not includi ng 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 fr om 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 adde d or removed, as necessary. A technical assessment of the CDM process is summarized in Table 43

.

Figure 43. CDM produced water treatm ent technology: process diagram. ( http://ipec.utulsa.edu/Conf2008/ Ma nuscripts%20&%20presentati ons%20received/Kimball_24.pdf ).RPSEA Project 07122-12
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118 Table 43. CDM Process Assessment.

Criteria Description/Rationale Status of technology This process has been tested on a co al 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 tailo red by adding and removing unit processes to meet different product water criteria. Recovery Depends on feed water qua lity 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 numb er 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. Othe r 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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119 Veolia Water Solutions and Technologies: OPUS TM – optimized pretreatment and separation technology
N.A. Water Systems, a Veolia Water Solutions and Technology company, designed the

OPUS TM system. OPUS TM is a proprietary optimized pretreat ment and unique separation process for desalination of water with high concentra tions of sparingly soluble solutes (e.g., SiO 2 , CaSO 4 , and Mg(OH) 2 ), organics, and boron. The system is able to achieve high recovery with high purity product water through the use of extens ive 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: OPUS TM CBM produced water treatment system (Source: [153]).

The process first performs acidification and dega sification of the raw feed water. This is followed by an aggressive, conventional coagulati on, flocculation, and hi gh-rate plate settler sedimentation process, which is termed Multiflo TM chemical softening in the OPUS TM literature [153]. After this step, the feed stream should be devoid of n early all high-molecular-weight organic molecules and oxidized metals (particu larly 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 mol ecular weight hydrophobic organic molecules, including any remaining oil and grease.
Filtrate from the media filter is then processed through a mi xed, 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 w ith the RO membranes. The water is then pre ssurized and treated by BWRO membranes at an elevated pH. Operating the
RO elements under this condition reduces the f ouling propensity of silica and increases the rejection of both silica and boron. In April of 2008 the OPUS TM system was field tested at a steam-enhanced oil production site in San Ardo, CA. The tested OPUS TM 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

OPUS TM is described by the manufacturer as high, and may be equivalent to that of other high recovery RO systems that operate with elevated pH. OPUS TM 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 cons idered similar to that for BWRO processes.RPSEA Project 07122-12
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120 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 Mutliflo TM pretreatment compon ent requires significant chemical input in the form of acids (possibly HCl or H 2 SO 4 ), coagulants (potential chemicals
include Fe 2 (SO 4 ) 3 and Alum), alkali compounds (likely Ca(OH) 2 ), and polymer aids (candidates include polyDADMAC or PAC) [110]. Additiona l chemical demand is created by the IX regenerant solution that may requi re both acid and base regenerant s, as well as base chemicals required to increase the pH of the RO feed water.

OPUS TM 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 OPUS TM system likely requires substantial process automation and control. Moderate operator ove rsight may be required, especially for management of the Multiflo TM pretreatment system.
OPUS TM represents a highly flexible and robust treatment process a nd can operate with highly variable feed water quality. With proper ma nagement the system likely requires minimal
down time and maintenance. Cost fi gures related to capital, and ope rating 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: OPUS TM

– optimized pretreatment and separa tion technology is summarized in Table 44

.

Table 44. Summary of technical assessment for Veolia Water Solutions and Technologies:
OPUS TM – 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 a pplication 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 qua lity 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.
Mutliflo TM pretreatment process along with chemical storage components is the primary factors in limiting mobility. Energy consumption Energy requirements are unknown.RPSEA Project 07122-12
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121 Table 44. Summary of technical assessment for Veolia Water Solutions and Technologies:
OPUS TM – optimized pretreatment and separation technology.

Criteria Description/Rationale

Chemicals Multiflo TM pretreatment system will requi re 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, Na 4 EDTA, or HCl. IX process will require regeneration with strong acid, likely H 2 SO 4 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 syst ems 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 re quired. Relatively high recovery rates exceeding 90% generate very minor amounts of concentrated brine. Sludge from the sedimentation basin w ill 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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122 New Logic Research: V  SEP ® - Vibratory Shear Enhanced Membrane Filtration

T he 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 produ ced by the membrane vibr ation 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 processi ng exposes the m embrane pores for maximum throughput th at is typically between 3 and 10 times the throughput of conventional cross-flow systems [1 55]. Compared to conventional RO systems, V  SEP ® is not limited by the solubility of minerals or the presen ce of suspended solids. It can be used in the same applications as crystallizers or brine conc entrators 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.

F igure 45. Fouling reduction mechanisms of V  SEP ® (Source: [155]).

The manufacturer claims that the V  SEP ® process has several advantages over conventional membrane pro cess [157]. These include:

 Minimal pretreatment: Because of high sh earing energy at the membrane surface and near the pores, colloidal f ouling and concentration polar ization are greatly reduced. The use of pretreatment to prevent scale formation is not required.

 Low fouling and scaling potential: Sinus oidal shear waves from the membrane surface help to repel appro aching 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 allo wing free transport of the liquid through the
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123  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 foot print of the unit. As much as 2000 square feet (185 m 2 ) of membrane is contained in one V  SEP ® module with a footprint of
4x4 ft.

The combined advantages make V  SEP ® an attractive technol ogy 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 No rth Sea, Latin America, and Alberta's Oil Sands [158]. Several pro duced 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 pr ocess and is using steam generators in the operations to enhance oil producti on. Re-injection of produced water into the source formations was the method of disposal. After on-site trials, BreitBurn dete rmined 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 alka linity, 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 asphalte nes that are colloidal materials that do not readily separate using conventional methods. Aspha ltenes tend to adsorb at water-in-crude oil interfaced to form a rigid film surrounding the in terface. A schematic drawing of the BreitBurn treatment process is shown in Figure 46 . The treatment employs bot h NF and RO m embranes. The final permeate, after two stag es of filtration, has a non-detect able 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.RPSEA Project 07122-12
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124 Figure 46. Schematic of the BreitBurn tr eatment 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 a nd 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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125 Table 46. Summary of tec hnical 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 e xpected 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 adap t to highly varyi ng water quality and quantity. The level of robustness and reliability n eed 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, re mineralization 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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126 Eco-Sphere: Ozonix TM

Eco-Sphere has developed a semi-truck trai ler-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 packag ed 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 pumpe d into a reaction vessel and is flash mixed with supersaturated ozonated water. The ozone is decomposed into hydroxyl radicals by u ltrasonic transducers, which readily oxidizes metals, decomposes soluble and insoluble organic compounds and microorganisms. Ultrasonic tr ansducers also induce cavitations among the dissolved ozone bubbles, which act to induce shearing of larger particles and decreas es 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 th e solution to facilitate pa rticle coagulation. The ozonated, coagulated water is then passed throu gh 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 i norganic solutes [159, 160]. A proof-of-concept pilot study was conducted with the Ozonix TM system in the Woodford Shale Play in November of 2008 [160]. Newfield Exploration Mid-Continen t, 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 ina 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 as surance 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 en ergy consumed to treat 1,300 bbl (54.6 kgal) of water. Based on these calculations, the specific en ergy consumption per bbl of water treated is 2.2 kWh/bbl (52 kWh/kgal). The manufacturer cl aims that purified water recovery may exceed 75%, and only 1% of the initial bulk volume n eeding 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 antisca lant. The pilot system required three people to operate; however, the manufacturer estimates th at only two operators would be required with further process automation. A technical asse ssment of the Ozonix treatment process is
summarized in Table 47

.

Table 47. Summary of technical assessment for Eco-Sphere: Ozonix TM process. Criteria Description/Rationale

Industrial status Pilot scale study with frac wa ter 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.RPSEA Project 07122-12
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127 Table 47. Summary of technical assessment for Eco-Sphere: Ozonix TM process. Criteria Description/Rationale Production efficiency (recovery) Pilot study reports purified water recove ry 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 sy stem 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 demonstr ated 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 stabilizati on may be required for RO permeate

stream.
Concentrate
management or waste disposal Any remaining brine stream will requi re disposal through injection.

Applicability for produced water

treatment Excellent – Treatment provides robust pr etreatment to limit organic and hard salt loading on high-pressure membranes.

Note: 1 barrel = 42 US gallons

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128 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 tr eat a wide range of produced water compositions and produce clean water that may then be discha rged or reused. This technology was specifically developed for the desalination of oil and gas pr oduced waters. Pilot scale systems have been
tested in Texas A&M la boratories 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 o il, suspended solids, or dissolved hydrocarbons. The pretreated water is then further purifie d with polymeric UF and RO. The UF system provides a final barrier to suspended solids (suc h 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 Texa s 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 TS S, 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, respectiv ely, corresponding to 98.7% TDS rejection. When incl uding the coagulation/flocculati on pretreatment process, total treatment costs were estimated to average $0.94 per barrel.

A second field trial was conduc ted at a CBM well field in Western Wyoming [162, 164]. The GeoPure treatment process was tested w ith CBM produced water containing corrosion inhibitor, alcohols, and surfactan ts. Other feed water parameters include a feed TDS of 9,700 mg/L (dominated by NaCl) and 41 mg/L of dissolved hydrocar bons. 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 assessmen t for GeoPure Water Technologies, LLC.

Criteria Description/Rationale

Industrial status Oil and natural gas related fi eld trials have reporte dly 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 wate r with TDS ranging from 9,700 to 15,000 mg/L. Frac flowback water constitute d 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.RPSEA Project 07122-12
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129 Table 48. Summary of technical assessmen t 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 chem ical 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 FeCl 3 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 syst ems 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, wh ile operation and management costs for the Barnett Shale Trend study seen a bove 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 acc ount of relatively low recovery rate. Sludge from the sedimentation basin w ill 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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130 Geo-Processors: Sal-Proc TM , ROSP, and SEPCON

Sal-Proc TM , linked RO – Sal-Proc ( ROSP ), and Saline Effluent to Products Conversion ( SEPCON ) are all treatment tec hnologies developed by Geo-Processors USA, Inc

. The SalProc TM technology is at the heart of both ROSP a nd SEPCON systems, and is a patented technology. The process was design ed to facilitate the sequentia l or selective precipitation and extraction of specific dissolved chemical compounds and salts from saline waters. Depending on the chemical composition of the saline feed st ream, 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-Proc TM system (Source: [165]).

The final product of the Sal-Proc TM system is a refined chemical salt that may have commercial value; depending on feed water quality these salts may include CaSO 4 , Mg(OH) 2 , NaCl, CaCl 2 , NaOH, CaCO 3 , and Na 2 CO 3 [166]. When the Sal-Proc technology is integrated with a RO treatment system, the combined system is termed ROSP. The combination of th ese processes enables th e conversion of saline impaired water into fresh water and useful chemical compounds. ROSP systems may employ
Sal-Proc TM as a pretreatment process for removal of sp aringly 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 in stallation that utilizes Sal-Proc TM , or by natural extension, ROSP subsystems as part of their brine management strategy. A SEPCON demonstration and testing facility is currently under c onstruction in California (2009). SE PCON systems are expected to have reduced operating costs with increase d feed water throughput [165]. The number of possible system configurations that could utilize a Sal-Proc TM subsystem is too numerous to list; therefore, the remainder of th is technology’s technical summary focuses on the stand-alone SalProc TM process.RPSEA Project 07122-12
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131 The Sal-Proc TM system has undergone a sustained period of development and improvements including field trials, pilo ting, and public demonstrations. Sal-Proc TM systems have been employed at various installations with treatment capaci ties between 217,151 to 2,111,000 gpd (5,170 to 50,250 bpd). The Sal-Proc TM 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-Proc TM 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-Proc TM
process has a theoretical recove ry of 100%. However, the final 15% of water removed from a feed solution are not likely to be captured for beneficial use. Infr astructure requirements for SalProc TM systems may be relatively high, and will likely require significant footprint to accommodate chemical reagent storage and product salt storage. The Sal-Proc TM is relatively mobile, and may be constructed to opera te out of a cargo trailer. Sal-Proc TM is designed to be highly modular and read ily integrated into other unit processes. Energy requirements for the Sal-Proc TM system are unspecified. However, available data indicates that the system has a capital co st 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 proce ss requires chemical r eagents to produce sal eable 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 ov ersight may be required to optimize reagent dosing and recovered salt management. Minimal pr etreatment 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-Proc TM process is shown in
Table 49

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132 Table 49. Summary of techni cal assessment of Sal-Proc TM process. Criteria Description/Rationale

Industrial status Full-scale application for produ ced 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 relativel y large to accommodate for chemical reagent and product chemical storage, as well as cleaning chemical storage.
Individual Sal-Proc TM 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 pr etreatment. 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-Proc TM process. High level of flexibility: easy to adap t to highly varyi ng water quality and quantity. Highly robust process. Reliability needs to be demonstrat ed through long-term operation. Types of energy required: electrical.

Overall costs The capital and construction costs of Sal-Proc TM 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 orga nic matter. Salts may be selectively removed from the feed solution to pr oduce water quality suitable for surface discharge.

Concentrate
management or waste disposal Any remaining brine stream will requi re disposal through injection.

Applicability for produced water

treatment Excellent – Capable of near zero liqui d 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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133 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. Hi gh sodium concentrations in waters reduce the permeability of clay-bearing soil and adversel y 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 a dverse effects to distribution systems, soils, and crops. Sodium adsorption ratio (SAR), along with pH, ch aracterizes salt-affected soils. It is an easily measured property that gives information on the comparative concentrations of sodium (Na + ), calcium (Ca 2+ ), and magnesium (Mg 2+ ) 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 ph ysical 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 so urce 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 lim estone (calcite or dolomite) filters. The addition of slaked lime ( calcium hydroxide) to produced water can provide calcium and alkalinity (i.e., hydroxi de alkalinity) as well as to adjust product water pH. WhenRPSEA Project 07122-12
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134 adding lime to water, it is importa nt 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 a dding calcium and magnesium to produced water does not reduce sodium, but changes the ratio of sodium to ot her salts. Although the SAR is decreased by adding hardness, the produced water beco mes more saline with the sodium salt still dissolved in the water. This approach is not likely to work w ith CBM product water that is sodium bicarbonate type. The added hardness (calcium) will comb ine with carbonate from the CBM water and precipitate out as ca lcium carbonate (lime). SAR treatment may require th e addition of acid (e.g., H 2 SO 4 ) to help degassing carbonate and dissolve the lime and produce the desired ha rdness 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 ir rigation 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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135 Constructed Wetlands
The development of constructed wetlands st arted approximately 40 years ago to exploit the biodegradation ability of plants [19]. Wetla nd 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 th rough the system . In vertical flow system ( Figure 48 ) water flows through layers of soils a nd 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 fr equency of inundation, wh ere 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 provi de an approach to treat ra w produced water or as posttreatment to further clean treated water. Res earch sponsored by Marathon Oil Company in 2000
involved construction of an artif icial sedge wetland system to treat CBM produced water. The purpose of the project was to determine if cons tituents 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 sy stem could effectively treat iron and possibly barium, but not change SAR . A report by Montana State Univer sity 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 wa ter 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, we tlands are proposed to be used as treatment systems. Wetlands could be designed for speci fic desired results, depending on produced water quality and prevalent envi ronmental conditions [169].RPSEA Project 07122-12
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136 The advantage of the constructed wetland systems includes low construction and operation costs (Cooper, et al., 1996, cited from All consulting repor t [168]), approximately 1 to 2 cents/bbl. Kuipers estimated the constructed wetla nds 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 orga nic removal treatment is 20 years and provides
excellent wildlife habitat.
Constructed wetlands have seve ral constraints on their usef ulness: 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) Pe riodic release of captu red 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 spra y the inflow water in the air. This would cause the fresh water to freeze (som e would evaporate as well), and the remaining water would be more concentrated in respect to the salts [171]. For engineered wetlands, the change in TD S due to significant evapotranspiration is important to consider in a hot and dry climat e [172]. Desalination process located downstream from the engineered wetland may be needed to re duce the TDS concentration to required effluent
concentrations. Various plant types have been studied and iden tified 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 hal ophytic plants which have dense fibrous root systems, uptake salts and sodi um, 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 bi rds 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. Fo r example, the research conducted by the USGS
has demonstrated acute and chronic sodium bicar bonate toxicity to aquatic species. The CBM produced water discharges containing selenium in concentrations above 2 mg/L may cause bioaccumulation in sensitive specie s [173]. In addition, if the wetla nds 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 asse ssment of constructed wetlands.

Criteria Description/Rationale

Industrial status Industrialized technology. Have been used for produced water management. Feed water quality bins In general < discharge li mit 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.RPSEA Project 07122-12
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137 Table 53. Summary of technical asse ssment 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 operati on and maintenance is assumed to consist of repairs to the piping and wetlands sediment remova l requiring equipment for one week and 22.5 days labor [170].

Overall costs Capital costs are highly variab le 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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138 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 contai n key trench-type excavations or closely spaced boreholes to enhance infiltration. Evapor ation also may be enhanced by atomizers placed on towers situated on floating islands, with sp ray 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-fa bricated pond liner. Nutr ient uptake is also possible through various biological processes that could facilit ate additional uses [19]. In Wyoming, approximately 3,000 infiltration p onds are either currently in use or are in the permitting stage [175]. Similar use of infiltr ation ponds in Montana is expected as CBM development expands. Infiltration ponds have se veral advantages. They are an inexpensive means of disposing of produced water, and allo w more flexibility in pumping rates for the developer/operator. Also, the pr oduced 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 incr ease 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 evalua tion [19]. The infiltration ponds also have se veral potential disadvantages. The infiltrated wate r 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 sh allow aquifers or streams. Predicting changes in water quality is an integral part of permitting these ponds [175].
Researchers at the Montana Bureau of Mi nes and Geology are developing methods to assess proposed CBM infiltration pond sites and to test and calibrate t hose methods with field
research. This will determine what criteria will be needed for the appropriat e siting of infiltration ponds. The technical assessment of infiltration p onds for produced water disposal is summarized

in Table 54

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139 Table 54. Summary of technical as sessment 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 qualit y through infiltration, including different removal rates of organic matter, suspended solids, nutrients and metals. Production efficiency (recovery) Variable and site specific. Water ba lance 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 operati on 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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140 Big Cat Energy Corporation: Aquife r Recharge Injection Device (ARID)
The aquifer recharge injecti on device (ARID) is a separati on technology that allows for the production of natural gas from a coal seam w ithout 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 cylindri cal mandrel has several rubber o-rings that are used to seal the mandrel, like a plug in the bore hole. The mandrel has four machined ports; these four ports are used for water and gas conveyanc e, a pump cable, and a transducer. A submerged pump is attached to the bottom of the mandrel w ith 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 identi fied saline aquifer through perfor ations 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. Duri ng pumping CBM gas accumulates in the headspace
created between the mandrel and water level of th e coal seam. This gas is recovered through the mandrel with a pipe that leads to a surface compre ssion 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 NP DES 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 expect ed to undergo field trials in 2009 [177]. Beyond the Powder River Basin, this simp le 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 assimi lative hydraulic capacity.
Trivial technical literature combined with the absence of field trial data makes it difficult to
discuss the broader merits and di sadvantages of th is technology.

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141 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 so lutions was tested on three separate polyvinyl diflouride (PVDF) polymeric UF membranes. Each unidentified UF membra ne was subjected to six different bench-scale fouling scenarios with two different f eed water flow rates and three different transmembrane pressures. Each of th e cleaning solutions was developed with various types of alkylpolyglycoside deriva tives 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 vari ous cleaning solutions is not disclosed [178]. Experimental results from the Texas A&M st udy indicate that ce rtain 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 (J cleaned /J uncleaned ) ranging from 1.15 to 7.53, with an aver age of 2.73 and a standard deviation of 2.14 for the nine different cleaning solutions.

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142 

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152 [129] W.F. Heins, and R. McNeill, Vertical -tube ev aporator system provides SAGD-quality feed water, WorldOil Magazine 228 (2007)

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153 [143] D. Beagle, CBM Produced Water Manageme nt in the Powder River Basin of W yoming and Montana, Canadian Society for Unconvent ional Gas, Calgary, February 13, 2008.

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154 [158] M. Galimberti, VSEP Solutions for Pr oduced Water, Desalters & SSW, Crude Oil Quality Group presentation (2007)

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156 

### ACRONYMS

AEM – Anion Exchange Membranes AGMD – Air Gap Membrane Distillation ARID – Aquifer Rechar ge 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

DP 3 RO TM – Double Pass, Preferential Precip itation, Reverse-Osmosis process ED – Electrodialysis
EDI – Electrodeionization EDR – Electrodialysis Reversal EVRAS – Evaporative Reduc tion 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

HERO TM – 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 SystemRPSEA Project 07122-12
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157 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 Power TM 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 Compre ssion 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