TECHNICAL SUMMARY OF OIL & GAS PRODUCED 

WATER TREATMENT TECHNOLOGIES 

J. Daniel Arthur, P.E. 

Bruce G. Langhus, Ph.D., C.P.G. 

Chirag Patel 

ALL CONSULTING, LLC 

1718 South Cheyenne Ave., Tulsa, OK 74119 

Ph: 918 382 7581 

Fax: 918 382 7582 

Abstract 

The objectives of oil and gas produced water treatment include meeting discharge 

regulations (local, state and federal), reusing treated produced water in oil and gas 

operations, developing agricultural water uses, rangeland restoration, cattle and animal 

drinking water, water for human consumption, and meeting water quality requirements 

for miscellaneous beneficial uses. Current produced water technologies and their 

successful applications have advantages and disadvantages and can be ranked on the 

basis of those factors. This paper attempts to describe, summarize and analyze various 

produced water treatment systems developed by oil and gas producers, research 

organizations, water treatment service companies, and universities. Treatment 

technologies, furthermore, have applicability to different kinds of produced water from 

strong brines to brackish waters. 

Acknowledgements 

 This paper was done as part of a research project funded by the National Energy 

Technology Laboratory (NETL) of the US Department of Energy (DOE). ALL Consulting and 

the Interstate Oil and Gas Compact Commission (IOGCC) as co-researchers are joined by the 

cooperating oil and gas agencies of several oil and gas producing states. The authors wish to 

thank the DOE and our co-researchers for their support. 

________________________________________________________________________ 

 March 2005 

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Introduction 

 Water produced during oil and gas extraction operations constitutes the industry’s 

most important waste stream on the basis of volume. The oil and gas industry produces 

approximately 14 billion bbls of water annually [1, 2]. The water varies greatly in quality 

and quantity and in some cases the water can be a useful by-product or even a salable 

commodity. Produced water is most often considered a waste, but the industry is 

beginning to consider this material as a potential profit stream. Whether waste or 

commodity, produced water has management costs that need to be kept in-line with each 

specific production project and region or it could adversely affect the life of the well, 

thereby leaving substantial recoverable reserves in the ground. Produced water handling 

practices must also be environmentally protective or the operator could face regulatory 

action. Produced water handling methodology depends on the composition of produced 

water, location, quantity and the availability of resources.

Some of the options available to the oil and gas operator for managing produced water 

might include the following: 

1. Avoid production of water onto the surface – Using polymer gels that block water 

contributing fissures or fractures or Downhole Water Separators which separate water 

from oil or gas streams downhole and reinject it into suitable formations. This option 

eliminates waste water and is one of the more elegant solutions, but is not always 

possible. 

2. Inject produced water – Inject the produced water into the same formation or another 

suitable formation; involves transportation of produced water from the producing to 

the injection site. Treatment of the injectate to reduce fouling and scaling agents and 

bacteria might be necessary. While waste water is generated in this option, the waste 

is emplaced back underground. 

3. Discharge produced water – Treat the produced water to meet onshore or offshore 

discharge regulations. In some cases the treatment of produced water might not be 

necessary. 

4. Reuse in oil and gas operations – Treat the produced water to meet the quality 

required to use it for drilling, stimulation, and workover operations. 

5. Consume in beneficial use – In some cases, significant treatment of produced water is 

required to meet the quality required for beneficial uses such as irrigation, rangeland 

restoration, cattle and animal consumption, and drinking water for private use or in 

public water systems. 

Treatment of produced water has been attempted and is proven to be an effective option 

for produced water handling. Studies conducted to identify, verify and compile existing 

and newly developed techniques demonstrate the economical benefits of produced water 

treatment. Treating oilfield water can help facilitate additional water management options 

for operators such as beneficial uses that in the short and long term can potentially 

provide certain community and economic advantages. Treated produced water has the 

potential to be a valuable product rather than a waste. The treatment of produced water is 

a necessity before the majority of the conventional produced waters can be applied to 

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other uses. The general objectives for operators when they plan produced water treatment 

are: 

1. De-oiling – Removal of free and dispersed oil and grease present in produced water. 

2. Soluble organics removal – Removal of dissolved organics. 

3. Disinfection – Removal of bacteria, microorganisms, algae, etc. 

4. Suspended solids removal – Removal of suspended particles, sand, turbidity, etc. 

5. Dissolved gas removal – Removal of light hydrocarbon gases, carbon dioxide, 

hydrogen sulfide, etc. 

6. Desalination or demineralization – Removal of dissolved salts, sulfates, nitrates, 

contaminants, scaling agents, etc. 

7. Softening – Removal of excess water hardness. 

8. Sodium Adsorption Ratio (SAR) adjustment – Addition of calcium or magnesium ions 

into the produced water to adjust sodicity levels prior to irrigation. 

9. Miscellaneous – Naturally occurring radioactive materials (NORM) removal. 

Selection of produced water treatment structure is often a challenging problem that is 

steered by the overall treatment objective. The general plan is to select the cheapest 

method – preferably mobile treatment units which assure the achievement of targeted 

output criteria. In this way technology can be positioned in the field for optimum 

convenience and the technology can be fine-tuned to meet specific end-uses for the water. 

The following sections discuss the major objectives of produced water treatment, the 

technology alternatives commercially available at the present time, and a summary of the 

advantages and disadvantages of the various technologies. 

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Produced Water Treatment Objectives 

Produced water usually represents a waste product in the petroleum industry; it is more 

often than not only a cost that must be controlled to enhance project economics. Water 

management and cost control can be done by choosing appropriate water disposal options 

or by finding an appropriate beneficial use for the water. Waste options and beneficial 

uses are, however, highly dependent upon water quality and may require water treatment 

prior to disposal or use. Treatment of produced water may be required in order to meet 

pre-disposal regulatory limits or to meet beneficial use specifications. If the oil and gas 

operator aims to utilize a low-cost disposal option such as discharge to surface waters, the 

produced water must meet or exceed limits set by regulators for key parameters. The 

parameters might be specific constituents of concern such as ammonia or barium that can 

be toxic to sensitive animal and plant-life. Or the parameters may be more broadly-based 

such as Total Dissolved Solids (TDS) or Sodium Adsorption Ratio (SAR) that can affect 

several aspects of the environment. The regulatory community may make these limits 

seasonal so that spring run-off water is more carefully protected. In that case treatment 

options may also be seasonal. 

If the oil and gas operator wishes to convey his produced water to a secondary user, the 

operator must be sure that the water falls within the specifications of the user. 

Specifications might be chemical (e.g., TDS), physical (temperature), or biological 

(coliforms per L). Specifications, regulatory limits and produced volume will define 

treatment objectives for the operator. Produced water treatment objectives may be 

mandated for several reasons and may be made necessary because of the presence of a 

number of constituents. The section below discusses some of these common treatment 

objectives. 

Oil and Grease Removal (De-oiling) 

Oil and grease in produced water includes free oil, dispersed oil (small oil droplets), and 

emulsified oil. Oil and grease discharge, along with produced water, involves compliance 

with stringent regulations. For example, monthly average oil content of 29 ppm (analyzed 

by EPA 1664 A) in dischargeable produced water is allowed for offshore operations in 

the Gulf of Mexico. 

Oil and grease removal methods depend on the end usage of treated water and 

composition of oil in the produced water. 

Table 1 [2] shows typical performance for oil removal treatment as expressed by oil 

particle size. 

 

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Table 1 – Oil and grease removal technologies based on size of removable particles. 

Oil Removal Technology Minimum size of particles removed 

(microns) 

API gravity separator 150 

Corrugated plate separator 40 

Induced gas floatation (no flocculants) 25 

Induced gas floatation (with flocculants) 3 – 5 

Hydroclone 10 – 15 

Mesh coalescer 5 

Media filter 5 

Centrifuge 2 

Membrane filter 0.01 

 (Source: Argonne National Laboratory)

The performance of API gravity separators depends on retention time, tank design, oil 

properties, operating conditions and the effects of flocculants or coagulants if added. 

Gravity separation is ineffective with small oil droplets or emulsified oil. As the oil 

droplet size diminishes, the required retention time drastically increases in order to obtain 

efficient performance. Gravity separation of smaller droplets also requires higher capital, 

maintenance and cleaning costs. 

Corrugated plates are packed to enhance the performance of gravity separation tanks 

(Figure 1). The oil droplets coalesce and form larger oil droplets as the corrugated plates 

provide a longer path for the oil droplets to travel to the top of the tank. It is a simple 

operation that allows the compact design of the API separation tank; however, the 

efficient oil removal limits the oil droplet size of 40 microns and larger. Removal of 

smaller oil droplets is difficult with corrugated plate separator. 

Gas floatation units use air/gas to float out oil more rapidly from the produced water. The 

density of oil particles reduce as they attach to gas bubbles. Reduced density improves 

the speed of oil floatation to the surface. The oil lumps on the surface are skimmed off. 

There are two types of floatation systems; dissolved air floatation and induced gas 

floatation. Dissolved air floatation uses an air compressor to inject and dissolve air into 

the produced water steam. 

Induced gas floatation (Figure 2) creates fine gas bubbles through mechanical, hydraulic 

or sparging systems. The induced gas bubbles adhere to the oil droplets as they move 

upward to the surface. It provides high oil removal efficiency at larger throughput or 

lesser retention time for a given rate. Efficient performance is limited to oil droplet size 

of greater than 25 microns. To achieve higher efficiency if smaller droplets are present, 

flocculants and coagulants are added to improve the performance. Produced water 

treatment systems based on micro-bubble floatation system have been developed which 

use 5-50 micrometer bubbles through the reactor [3]. Smaller bubbles more effectively 

separate oil from the produced water which results in low skim volume (Figure 3). 

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Figure 1 – Corrugated Plate (CPI) packing separates oil and solids from produced water 

 (Source: NATCO Group) 

 Figure 2 – Induced gas floatation cell (Source: NATCO Group) 

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 Figure 3 – Oil droplets coalesce on the surface as oil micro bubbles adhere to them 

 (Source: GLR Solutions Ltd., Canada) 

 Figure 4 – A vessel containing multiple hydrocyclones for de-oiling of produced water 

 Maximum capacity – 120,000 barrels/day (Source: NATCO Group) 

Hydrocyclones generate spinning motion of the fluid that creates centrifugal force to push 

heavier water outward and lighter oil into the middle core of the cones. The water 

continues down and exits out the tapered end. The improved gravity effect provides a 

higher rate of separation. The oil removal efficiency is higher with multi-cone (Figure 4) 

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modules that achieve small installation footprints. The devices are easily accessible and 

work even with high oil concentrations. The drawbacks of the operations are larger 

pressure drop across the device, inability to remove solids, higher maintenance costs and 

susceptibility to fouling and blockages from solids buildup. 

Centrifuges operate on the same physical principle as hydrocyclones, but unlike 

hydrocyclones where tangential feed inlet generates centrifugal force, moving parts 

generate the spinning motion. They also remove suspended solid. It handles solid 

particles as small as 2 microns. The disadvantages of centrifuges include low throughput 

and high maintenance costs. 

Macroporous polymer extraction (MPPE) treatment uses a packed column containing 

porous polymer beads with pore size of 0.1 to 10 microns. The polymer beads are filled 

with a specific extraction solvent. The solvent extracts dispersed oil and polycyclic 

aromatics from the contacting produced water stream [4]. In-situ generation of extraction 

liquid is accomplished by periodically stripping the extracted hydrocarbons with low 

pressure steam. 

Soluble Organics Removal 

Extraction of dissolved hydrocarbons with on-site liquid condensate (such as available 

from gas compression units) has been attempted by some oil and gas producers. 

Extraction enables enhanced removal of dispersed oil by coalescing small oil droplets 

during the process [5]. This process utilizes the principle of higher solubility of heavier 

hydrocarbons in lighter hydrocarbons. 

Adsorption is a widely accepted technology for the removal of soluble hydrocarbons 

from the produced water. Adsorption columns are packed with porous solid material 

known as adsorbent. The hydrocarbons present in the produced water adhere onto the 

surface of adsorbent and are eventually retained within the porous structure. The effluent 

from the adsorption column contains little or no hydrocarbons. Highly porous adsorbents 

with higher surface area offer better performance. Activated carbon, nutshell media, 

modified organoclay, etc. are some of the adsorbents used for produced water treatment. 

The major concern of adsorption operation is the requirement of retention time which 

limits the throughput capacity. 

Oxidation of soluble organics and contaminants (bacteria, nitrate etc.) is an effective 

produced water treatment. Ozone and hydrogen peroxide are strong oxidizers. Oxidation 

process produce dissolved carbon dioxide which can be removed by air stripping. 

Ultraviolet (UV) light has also been used for oxidation, which de-ionizes water into 

hydrogen and hydroxyl ions. Hydroxyl ions are also strong oxidizers. UV light also kills 

bacteria and other microorganisms to disinfect the water. Advanced oxidation processes 

involving a combination of UV light and ozone or hydrogen peroxide have also been 

attempted. Oxidation is able to reduce chemical oxygen demand (COD), biological 

oxygen demand (BOD), organics, iron, nitrite, manganese, cyanides, pesticides, hydrogen 

sulfide and aromatic hydrocarbons. Biological decomposition (combined oxidation and 

reduction) of produced water in a constructed wetland is also useful for treating raw 

produced water and treating post-treatment water after it has been through other treatment 

ALL Consulting, LLC 8
processes. Plants and microorganisms are utilized to naturally decompose the 

contaminants from the produced water. 

Desalination 

Removal of dissolved solid, salts or impurities is often the most important part of water 

treatment systems. TDS in produced water ranges from <2000 ppm to >150,000 ppm. 

Average TDS content in seawater is approximately 35,000 ppm. The choice of 

desalination method depends on TDS content and compatibility of the treatment system 

to work under the presence of extra contaminants present in the produced water. Oil and 

gas operators have attempted evaporation, distillation, membrane filtration, electric 

separation and chemical treatments to remove TDS from the produced water. Various 

desalination technologies are discussed in the next section with their applications for the 

treatment of produced water treatment.

Disinfection 

Removal of bacteria, viruses, microorganisms, algae, etc. from the produced water is 

necessary to prevent scaling and water contamination. Microorganisms occur naturally in 

the produced water or may be added during de-oiling treatments. Advanced filtration 

techniques are one of the effective technologies used to remove microorganisms. UV 

light treatment, chorine or iodine reaction, ozone treatment and pH reduction are other 

treatments available to disinfect produced water. Some of the general and advanced 

disinfection treatments are discussed in the next section. 

Miscellaneous Treatment 

Produced water softening, SAR adjustments and removal of trace contaminants, 

pollutants, naturally occurring radioactive materials (NORM), etc. are the part of 

produced water treatment in some regions depending on the composition of produced 

water. 

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Produced Water Treatment Technologies 

 Treatment objectives can be addressed by treatment technology options. The 

options can differ in their inherent facility requirements, capital costs, operating expense, 

and waste streams; all three factors can be important to the oil and gas operator. Some 

technologies may have large space requirements that may not be possible in some oil and 

gas installations. Some technologies may be commercially available as small, skidmounted units that can be easily relocated as production conditions change. Equipment 

costs are obviously important in some installations where a large amount of dedicated 

equipment must be purchased just for managing produced water. Higher power costs and 

chemical expenses could be unsupportable early in the life of an oil and gas 

development. Treatment wastes derived from produced water may no longer be 

classified as oil and gas wastes and may be more difficult and more expensive to 

manage. This section discusses various produced water technologies and their 

applications in fulfilling treatment objectives described above. 

Packed Bed Adsorption 

ET Ventures, L.L.C., South Carolina field tested its new ET #1 produced water treatment 

system at RMOTC (Rocky Mountain Oilfield Testing Center) in July 1996 to determine 

its effectiveness in adsorbing hydrocarbons from produced water [6]. Water produced 

from the Tensleep formation was atmospherically cooled (to 90°F) and flowed through a 

three-stage packed bed adsorption treatment system. Higher temperature affects the 

removal efficiency of the adsorbent. The first two stages contained ET #1, a sodium 

bentonite modified organoclay adsorbent. The final stage contained granular activated 

carbon (GAC). The samples of inlet feed, effluent from ET #1 columns and effluent from 

the GAC column were analyzed by a standard EPA (EPA 1664-A) analytical testing 

method. 

Figure 5 – A mobile packed bed adsorption system for the treatment of produced water (Source: ET 

Ventures Inc) 

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Figure 5 shows a mobile treatment trailer used for the operation. The system was 

operated at 10 GPM flow rate and maximum 10 psi pressure drop. 

Table 2 shows the result obtained for one of the trials during the treatment. ET #1 

treatment was sufficient to remove TPH below detectable limits. Oil and grease values 

were below detectable levels after ET #1 adsorption treatment. BTEX were removed to 

below detectable levels after GAC adsorption treatment. 

Table 2 – Results from ET Venture’s mobile produced water treatment system 

Contents Before Treatment, 

ppm 

After Treatment, 

ppm 

Total Petroleum Hydrocarbons (TPH) 148 1.1 

Oil and Grease 151 1.2 

Benzene 3.14 <0.5 

Toluene 4.97 <0.5 

Ethylbenzene 4.95 <0.5 

Xylene 29.7 <1 

 

Decomposition in Constructed Wetland 

 The Department of Energy (DOE) Naval Petroleum Reserve No. 3 (NPR-3) bio-treatment 

facility with average throughput of 35,000 BPD of water is located in Natrona County in 

east central Wyoming [7]. The wetland treatment facility started in January 1996 to 

provide a cheaper alternative to reinjection and to benefit local wildlife by way of water 

discharge. Wetlands are thin film bioreactors that utilize various species of plants and 

microbes along with sands that oxidize contaminants present in the water. A schematic of 

treatment process is shown in Figure 6. 

Cooling Tower Cooling 

Trench

Netted Pond

Wetland

Cooling 

Trench

Creek Oxidation 

Figure 6 – DOE Naval Petroleum Reserve’s bio-treatment process

The process undergoes the following steps: 

1. Cooling tower followed by a shallow cooling trench to reduce the temperature of

produced water from 180 – 200°F to below 100°F. Higher temperatures reduce the 

performance of plants in the subsequent wetland pond. 

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2. Netted pond or skimming pond further cooled the water and also removed suspended 

solid and oil under gravity effects. Dispersed oil on the top surface was skimmed off. 

3. Specially developed flora and fauna including hydrocarbon decomposing bacteria, 

sulfate reducing bacteria, nitrifying and denitrifying bacteria, iron related bacteria, 

algae etc biodegraded various contaminants present in produced water. 

4. Microorganisms in wetlands degraded most of the hydrocarbons and the remaining 

traces of hydrocarbons are removed in an oxidation process. 

The produced water from the Tensleep formation was blended with the produced water 

from other formations before the treatment. The blending process reduced the level of 

some of the contaminants and also lowered the temperature. While TDS was not affected, 

certain persistent contaminants such as organics, alkalinity, and ammonia were greatly 

attenuated. Table 3 shows the result obtained using the bio-treatment facility. 

Table 3 – Summary of the performance of NPR-3 Bio-treatment facility which included wetland 

treatment 

Constituents Before treatment, ppm After treatment, ppm Overall removal, % 

NH3 2.03 0.54 73 

NO3 <0.1 <0.1 - 

Phosphorus 1.83 0.46 75 

BOD 28 2.3 92 

COD 48 29 40 

TOC 32.7 3.6 90 

TPH 112 5.8 95 

Oil & Grease 71.9 4.2 94 

Benzene 0.143 <0.001 100 

Toluene 0.135 <0.001 100 

Ethlybenzene 0.035 <0.001 100 

Xylene 0.162 <0.001 100 

Turbidity 45.4 4.76 90 

TDS 4380 4010 9 

Alkalinity 713 190 73 

Ion Exchange 

The ion exchange process effectively removes arsenic, heavy metals, nitrates, radium, 

salts, uranium, and other elements from the produced water. Ion exchange is a reversible 

chemical reaction wherein positively or negatively charged ions present in the water are 

replaced by similarly charged ions present within the resin. The resins immersed in the 

water are either naturally occurring inorganic zeolites or synthetically produced organic 

resins. When the replacement ions on the resin are exhausted, the resin is recharged with 

more replacement ions. 

 

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Ion Exchange Resins

Ion exchange resins are classified as cation exchangers, which exchange positively 

charged ions and anion exchangers, which exchange negatively charged ions. The resins 

are further classified as: 

Strong Acid Cation (SAC) Resins: 

The hydrogen or sodium forms of the cation resins are highly dissociated and H+

 or Na+

ions are readily exchangeable over the entire pH range. Equation 1 shows an example of 

salt removal with SAC. 

3 )(2 2 →+− − 4 + 2)( HClNiSORNiClHSOR ..(1) 

Equation 2 shows an example of Ca+

 softening with SAC. 

+ + +−→+− 2)()(2 HCaSORCaHSOR 2

3 3 ..(2) 

These resins would be used in the hydrogen form for complete deionization (Na, Ca, Mg, 

Ba, etc. removal); they are used in the sodium form for water softening (Ca and Mg 

removal). After exhaustion, the resin is regenerated to the hydrogen form by contact with 

a strong acid solution, or to the sodium form with a sodium chloride solution. 

Weak Acid Cation (WAC) Resins: 

Weak acid resin has carboxylic acid (COOH) group as opposed to the sulfonic acid group 

(SO3H) used in strong acid resins. These resins behave similarly to weak organic acids 

that are weakly dissociated. WAC has high affinity for divalent salts. Equation 3 shows 

an example of Ca+

 softening with WAC. Alkalinity present in bicarbonate form can also 

be removed by WAC. 

+ + (2 COOHR −→+− 2 + 2)() HCaCOORCa ..(3) 

Free H+ ions can react with bicarbonate (present as hardness, Ca(HCO3)2) to form 

carbonic acid. The carbonic acid decomposes in carbon dioxide as shown in equation 4. 

Removal of carbon dioxide or decarbonation [8] is necessary during the water treatment 

process. 

3 →+ 32 +→ 22 OHCOCOHHHCO − + ..(4)

Weak acid resins exhibit a much higher affinity for hydrogen ions compare to strong acid 

resins. This characteristic allows regeneration to the hydrogen form with significantly 

less acid than is required for strong acid resins. Almost complete regeneration can be 

accomplished with stoichiometric amounts of acid. The degree of dissociation of a WAC 

is strongly influenced by the solution pH. Consequently, resin capacity depends in part on 

solution pH. 

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Strong Base Anion Resins: 

Strong base resins are highly ionized and can be used over the entire pH range. These 

resins are used in the hydroxide (OH-

) form for water deionization. They will react with 

anions in solution and can convert an acid solution to nearly pure water. Equation 5 

shows the reaction involved in an anion exchange step. 

( − 3 →+ () − 3 ) + HOHClNHRHClOHNHR ..(5)

Regeneration with concentrated sodium hydroxide (NaOH) converts the exhausted resin 

to the hydroxide form. 

Weak Base Anion Resins: 

Weak base resins exhibit minimum exchange capacity above a pH of 7. The weak base 

anion resins sorbs anions associated with weak acid. 

Applications 

Ion exchange has several applications in water treatment processes such as hardness 

removal, desalination, alkalinity removal, radioactive waste removal, ammonia removal 

and heavy metal removal. Since divalent ions (Ca, Mg, etc.) are favored over monovalent 

(Na, etc.) ions by the resin for replacement, secondary treatment for SAR (sodicity) is 

required. 

Powder River Gas, LLC: 

Powder River Gas, LLC proposed a Project Plan of Development (POD) [9] to drill and 

test for coal bed natural gas (CBNG) in eight federal and eight fee wells at eight locations 

(two wells per location) in an area northeast of the Tongue River Reservoir, Big Horn 

County of southeastern Montana. 

Part of their NO FEDERAL ACTION alternative was to treat water produced from the 

wells using a Higgins Loop (continuous counter-current ion exchange) treatment facility 

prior to discharging to the Tongue River. The proposed treatment facility will use 0.92 

acres of private surface. The stationary Higgins Loop facility will be constructed along 

with 0.5 acre-feet capacity impoundment and chemical storage tanks. All chemical 

storage tanks will be surrounded by a shallow spill containment berm to prevent any 

accidental chemical spills. 

Produced water from CBNG wells is to be treated stepwise within the treatment facility. 

Settling of suspended sediments and releasing of residual gas will be within the 

impoundment. Na+

, barium and other heavy metals from produced water will be 

removed using SAC resins in the Higgins Loop. Removal of CO2 produced during the 

ion exchange process and adjustment of pH will be achieved by adding calcium 

hydroxide. CO2 can be removed by air-stripping or membrane degasification. The 

physical law governing this process is the equilibrium between the gas phase and the 

concentration of the solute gas in the liquid phase. 

The schematic is shown in Figure 7. The Higgins Loop is a vertical cylindrical loop 

containing a packed bed of strong acid ion exchange resin that is separated into four 

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operating zones by butterfly (loop) valves. These operating zones (Adsorption, 

Regeneration, Backwashing and Pulsing) function like four separate vessels. 

 

 

 Figure 7 Higgins Loop schematic (Source: Seven Trent Services) 

The Higgins Loop treats liquids in the adsorption zone with resin while the ions are being 

removed from loaded resin in the regeneration zone simultaneously. Intermittently, a 

small portion of resin is removed from the respective zone and replaced with regenerated 

or loaded resin at the opposite end of that zone. This is accomplished hydraulically by 

pulsing of the resin through the loop. The result is continuous and countercurrent 

contacting of liquid and resin. The cations (Ca+

, Na+ etc.) are replaced by hydronium (H+) 

ions from resin beads. The hydronium ions are released in the treated water, which lowers 

the pH of the water. Cations are stripped from the resin in the regeneration zone 

concurrent with ion exchange in the adsorption zone. Dilute hydrochloric acid is injected 

into the loop and moves counter-current to the resin and the spent brine discharge, 

leaving the resin restored to the hydronium form. 

Concentrated brine volumes average approximately 1.0% of the total Loop feed volume, 

depending on the cation loading that is removed from the treated water. Excess brine that 

is not recycled to other beneficial uses is proposed to be transported offsite by truck for 

disposal injection into a permitted Class I, deep disposal well located in Wyoming. The 

waste stream from the treatment process, at maximum flow, will generate approximately 

60 barrels of brine or reject water per day. The treatment unit would discharge a total of 

250 gpm of treated water. 

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Figure 8 – A Higgins Loop in operation (Source: Seven Trent Services) 

EMIT Water Discharge Technology, LLC: 

EMIT Water Discharge Technology, LLC [10] developed a new treatment process that 

uses DOWEX G-26 (strong acid cation exchange resin manufactured by DOW Chemical 

Company). G-26 resin has sulfonic acid (SO3H+

) group that exchanges Na+, Ba+, Ca2+, 

and Mg2+

 etc ions with H+ ion. The ion exchange process is accomplished in a Higgins 

Loop. The Higgins Loop operation is followed by calcium addition to adjust pH, balance 

SAR and increase calcium concentration. Table 4 shows the results of a field trial for the 

treatment of produced water from Powder River Basin, Wyoming. The process focused 

on the removal of sodium ions and reduction of SAR using combination of Higgins loop 

and calcium addition. 

Table 4 – Performance of Higgins Loop treatment for a field trial at Powder River Basin site 

Constituents Influent Produced Water Treated Water Removal % 

Na, ppm 486 12 97.53 

Ca, ppm 22.2 113 -409 

Mg, ppm 13.2 <1 >93 

K, ppm 13.5 <1 >93 

Ba, ppm 0.72 ND 100 

Carbonate, ppm <1 <1 - 

Bicarbonate, ppm 1430 311 78.52 

Chloride, ppm 18 42 -133.33 

Sulfate, ppm 1 1.1 -10 

SAR 20.2 0.3 98.51 

pH 8.1 6.5 19.75 

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The increment in calcium, chloride and sulfate levels were due to chemical addition 

during SAR adjustment. The field trial was conducted with throughput of 200 GPM. The 

treatment cost ranges from $0.05 to $0.20 per barrel of treated water depending on the 

influent composition, SAR, and availability of resources. The ion exchange treated water 

may then be discharged to the environment and the residue disposed off [11].

Sandia Ion Exchange/Sorption Process: 

Sandia National Laboratory (SNL) reported use of Hydrotalcite (HTC) as anion 

exchanger and Permutite as cation exchanger [12]. These ion exchangers are comprised 

of durable inorganic oxides which provide stability over a large range of pH. Based on 

the results of various experiments, SNL reported average ion exchange capacity of HTC 

and Permutite as 2.5 mEq/gram (measured with Na2So4), and 1.7-2.7 mEq/gram 

(measured with NaOH) respectively. 

Water in

Lime in HTC in Permutite in

Treated 

water out 

UF

HTC 

regeneration/disposal

Permutite 

regeneration/disposal

Figure 9 – Ion Exchange/Sorption desalination process (Source: SNL) 

Anions in the inlet water are replaced by hydroxide ions (HTC anion exchange) and 

cations are replaced by hydrogen ions (Permutite cation exchange). Lime softening pretreatment is optional stage. 

Ion exchangers are regenerated after they are exhausted. In the regeneration process ion 

exchangers regain their ion exchange capacity. It may not be possible to regain 100% ion 

exchange capacity during regeneration process. SNL attempted to determine effects of 

regeneration on the ion exchange capacity of above mentioned ion exchangers and 

concluded that Permutite can regain ion exchange capacity without significant loss.

Regeneration of HTC at low temperatures was not promising, and at high temperatures 

regeneration became costly.

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Electrodialysis (ED) and Electrodialysis Reversal (EDR) 

Electrodialysis (ED) 

Most salts dissolved in water are ionic, being positively (cationic) or negatively (anionic) 

charged. These ions are attracted to electrodes with an opposite electric charge. 

In ED, membranes that allow either cations or anions (but not both) to pass are placed 

between a pair of electrodes. These membranes are arranged alternately. A spacer sheet 

that permits feed water to flow along the face of the membrane is placed between each 

pair of membranes. 

Figure 10 shows an ED assembly with feed spacer and ion exchange membrane placed 

between oppositely charged electrodes. Positively charged ions (Na+

 etc) migrate to 

cathode and negatively charged ions (Cl-

 etc) migrate to anode. 

Cathode 

( - ) 

Anode 

( + ) 

Figure 10 – An ED unit in operation (Source: Electrosynthesis Company Inc) 

During migration the charged ions are rejected by similarly charged ion exchange 

membranes. As a result, water within the alternate compartment gets concentrated 

leaving desalted water within the next compartment of the ED unit. The concentrate and 

desalted water are continuously removed from the unit. The basic electrodialysis unit 

consists of several hundred cell pairs bound together with electrodes on the outside and is 

referred to as a membrane stack.

ALL Consulting, LLC 18
Feed water passes simultaneously in parallel paths through all of the cells to provide a 

continuous flow of desalted water and brine to emerge from the stack. The feed water is 

circulated through the stack with a low-pressure pump with enough power to overcome 

the resistance of the water as it passes through the narrow passages. The raw feed water 

must be pre-treated to remove materials that could harm the membranes or clog the 

narrow channels in the cells from entering the membrane stack. A rectifier is generally 

used to transform alternating current (AC) to the direct current (DC) supplied to the 

electrodes on the outside of the membrane stacks. 

Post-treatment consists of stabilizing the water and preparing it for distribution. This 

post-treatment might consist of removing gases such as hydrogen sulfide and adjusting 

the pH. 

Electrodialysis Reversal Process (EDR)

An EDR unit operates on the same general principle as a standard electrodialysis plant 

except that both the product and the brine channels are identical in construction. At 

intervals of several times an hour, the polarity of the electrodes is reversed, and the flows 

are simultaneously switched so that the brine channel becomes the product water channel, 

and the product water channel becomes the brine channel. 

The result is that the ions are attracted in the opposite direction across the membrane 

stack. Immediately following the reversal of polarity and flow, enough of the product 

water is dumped until the stack and lines are flushed out and the desired water quality is 

restored. This flush takes about 1 or 2 minutes, and then the unit can resume producing 

water. The reversal process is useful in breaking up and flushing out scales, slimes and 

other deposits in the cells before they can build up and create a problem. Flushing allows 

the unit to operate with fewer pretreatment chemicals minimizes membrane fouling. The 

charges of the electrodes are reversed by a motorized valve. 

Applications 

Electrodialysis is conducted at low pressure drops across the process (usually less than 25 

psi). The pressure drop across the typical Reverse Osmosis (RO) membrane ranges from 

400 – 1400 psi which indicates higher energy consumption. 

Wind River Basin, Lysite, WY: 

The produced water from a conventional well in Wind River Basin of Wyoming [13]

contains H2S, oil, acid, BTEX, dissolved solids etc. About 93% of total TDS (8,300 to 

10,000 ppm) is accounted for as sodium, chloride, calcium and bicarbonates. Oil and 

grease content was about 65 ppm and BOD value was more than 330 ppm (contributed 

by acetates and volatile acids). The treatment trailer consists of the following units: 

1. De-oiling via induced gas floatation unit. 

2. Dissolved organics removal via two fluidized bed reactors. First was the anaerobic 

and nitrate consuming reactor for reducing large amount of organics. The second was 

the aerobic reactor ensuring oxidation of dissolved organics. 

3. Desalting/Demineralization using an ED unit. 

 

ALL Consulting, LLC 19
ED provided economical demineralization in this case. The feed water had approximately 

9,000 ppm TDS. As usual, the cost of the ED unit operation increases as the required 

TDS removal increases. Table 5 shows the overall removal of contaminants using 

different treatment technologies. The ED removed approximately 89% of TDS from the 

produced water. 

Table 5 – Produced water treatment performance at Wind River Basin, WY 

Parameter Influent, ppm Effluent, ppm Overall Removal, %

Oil and Grease 90 4 95.5 

BOD 330 51 84.5 

BTEX 11 0.1 99.1 

TDS (using ED) 9,100 1,000 88.9 

High Efficiency Electrodialysis (HEEDTM), Frac Water Inc: 

Frac Water Inc developed mobile ED treatment units for treating CBM produced water 

and reusing it in fracturing treatment. Several case studies suggest that the mobile 

treatment units treat the produced water with TDS ranges from 11,400 to 27,000 ppm and 

sulphates from 4,000 to 14,000 ppm [14]. ED provided the following benefits over RO:

1. ED can sustain high temperature; in fact higher temperature of produced water from 

the wellhead (140o

F) improved the conductivity and reduced resistance during ED 

process which leads to lesser voltage usage. Also higher temperature reduced 

viscosity. 

2. ED accepts feed water with Silt Density Index (SDI) value of 12 compare to SDI 

value of 3 for RO. Less SDI value indicates the necessity of pretreatment steps. The 

membranes are susceptible to fouling if feed water has high SDI. 

3. Certain level of fouling also occurs in ED operations. ED membranes can be cleaned 

or regenerated using weak acid treatment. 

4. Plate and frame configuration of ED system enables easier maintenance and cleaning. 

Figure 11 shows mobile ED treatment units from Frac Water Inc. ED treatment primarily 

recovers 80-90% of brackish water. The patents-pending electrodialysis HEEDTM stack 

configuration with dual or multiple side-by-side ion exchange membrane cells and improved 

gasket design results in greater separation efficiencies and affords greater flexibility in unit 

design. The improved design requiring up to 40% less membrane area resulted in over 70% 

increase in energy efficiency. 

ALL Consulting, LLC 20
Figure 11 – Mobile ED treatment trailer developed by Frac Water Inc 

Capacitive Deionization Technology (CDT) 

Capacitive deionization technology (CDT) is a new technology being developed for the 

purification of ocean and brackish ground water. A constant voltage is applied and 

soluble salts are collected on the surface of porous carbon electrodes, thus purifying the 

water for human consumption or industrial processes. In CDT, a brackish water stream 

flows between pairs of high surface area carbon electrodes that are held at a potential 

difference of 1.2 V. The ions and other charged particles (such as microorganisms) are 

attracted to and held on the electrode of opposite charge. The negative electrode attracts 

positively charged ions (cations) such as calcium (Ca), magnesium (Mg) and sodium 

(Na), while the positively charged electrode attracts negative ions (anions) such as 

chloride (Cl) and nitrate (NO3). Eventually the electrodes become saturated with ions and 

must be regenerated. The applied potential is removed, and the electrodes are flushed to 

release attached ions from the system, producing the more concentrated brine stream. 

The current carbon aero gel electrodes provide approximately 500 m2

/g surface area. 

They provide high electrical conductivity and high ion permeability. Carbon aero gel 

electrodes are expensive and their ion storage capacity is relatively low. The main 

problem is that the cost of the electrodes is too high due the high cost of the resorcinol 

(Resorcinol Fluoride, RF) from which the electrodes are made. TDA Research Inc has 

developed electrodes that provide higher surface area. CDT System Inc is developing 

impregnate of carbon nanotubes on the RF resins. 

ALL Consulting, LLC 21
Figure 12 shows conceptual diagram of CDT. Unlike ion exchange, exchange of ions 

does not occur; ions are adsorbed within the pores of charged electrodes under the effect 

of capacitance. 

 

Positive electrode attracts negatively charged ions (anions). 

Chloride (Cl-

) 

Nitrate (NO3

-

) 

Silica (SiO2

-

) 

Negative electrode attracts positively charged ions (anions). 

Sodium (Na+

) 

Calcium (Ca+

) 

Magnesium (Mg+

) 

 Figure 12 – A conceptual diagram of an AquaCell during CDT operation 

 (Source: TDA Research Inc.) 

Applications 

Desalination of produced water: 

Table 6 shows the result of the treatment of produced water from a CBNG well in 

Wyoming using CDT. 

Table 6 – Performance of CDT for the CBNG produced water treatment 

Constituent Before treatment After treatment 

Conductivity (micro s/m) 2,100 < 800 

Sodium ions (ppm) 280 84 

Bicarbonate ions (ppm) 520 144 

CDT Mobile Systems can also be used to produce drinking water and water for 

agriculture purposes at a low cost. Table 7 shows the throughput capacity of a 28 ft. 

mobile CDT unit, which includes 30 AquaCells with the capability to be field expanded 

ALL Consulting, LLC 22
to 88 AquaCells. The expected quality of treated water is fixed at 500 ppm TDS for 

drinking water and 1000 ppm TDS for agriculture water. 

Table 7 – Treatment capacity of CDT unit 

Feed Water TDS, ppm Capacity, Potable Water Capacity, Agriculture Water 

< 1,500 30,000 GPD 30,000 GPD 

2,500 20,000 GPD 27,000 GPD 

3,500 10,000 GPD 17,000 GPD 

4,000 5,000 GPD 12,000 GPD 

Source: CDT Inc, Dallas, TX

Electrochemical Activation (ECA) Technology 

Electrochemical Activation (ECA) technology is an innovative water disinfection 

technology which involves the exposure of water, and the natural salts, to a substantial 

electrical potential difference. As an anode (+) and a cathode (-) are placed in pure water 

and direct current is applied, electrolysis of water occurs at the poles leading to the 

breakdown of water into its constituent elements. If sodium chloride (NaCI), or table 

salt is used as a solution, the dominant electrolysis end product is hypochlorite, a chlorine 

based reagent, which is commonly used to disinfect water and kill microorganisms. This 

disinfection technology is currently used in series with the capacitive deionization 

technology in an activated water type of application. With this technology the natural 

water chemistry is used to produce highly effective disinfection agents that would destroy 

viruses and bacteria. 

Typically activated water would be dosed before and after the CDT AquaCells. Dosage 

before reduces the overall organic load into the AquaCells and also disinfects the feed 

stream, preventing biofouling. The dosage after the CDT AquaCells would then mainly 

serve as a final disinfection step specifically for potable water applications. Another 

benefit of the activated water technology is that the dosage before the AquaCells would 

also serve as a surfactant, thus reducing fouling, for example membrane fouling by 

CaCO3 (Calcium Carbonate) precipitation. 

Electro-deionization (EDI) 

Weakly-ionized species such as carbon dioxide, boron, and ammonia are difficult to 

remove via such membrane processes as reverse osmosis (RO) and electrodialysis 

reversal (EDR). EDI [15] is an electrically-driven membrane process. EDI combines ionexchange resins, ion-exchange membranes, and a DC electrical field. In EDI, ionized 

species are removed much like conventional electrodialysis (ED), with the rate of ion 

removal greatly increased by the presence of the ion-exchange resins in the cell. In the 

cell, the DC electrical field splits water at the surface of the ion-exchange beads, 

producing hydrogen and hydroxyl ions which act as continuous regenerants of the ionexchange resins. This allows a portion of the resins in the EDI to always be in the fullyregenerated state. Once ionized, these species are quickly removed under the influence of 

the DC electrical field. In effect, ionized species are removed in one area of an EDI stack, 

and weakly-ionized species are removed in a second area. 

ALL Consulting, LLC 23
Figure 13 shows the removal of ions as water travels through the EDI cell. Strongly 

ionized species are removed first in the flow path and weakly ionized species are 

removed as the water moves down the flow path. Removal of ionized species such as 

sodium, chloride, sulfate, and calcium by EDI is usually well over 99% and has been well 

documented previously. Removal of weakly-ionized species is an area where a properly 

designed EDI can also achieve extremely high removal rates. 

 Figure 13 – Schematic of an EDI cell (Source: Ionics Inc) 

Applications 

Ionics Inc has installed EDI units in various power plants and semiconductor plants in the 

US. Table 8 shows the average removal of weakly ionized ions using EDI in such plants. 

The results are based on the EDI operation only and no pretreatment or post treatment 

results are included. For example, EDI was able to remove approximately 97% of boron 

from the RO permeate. In this case RO was unable to effectively remove boron from the 

produced water. 

Table 8 – Average percentage removal of weakly ionized species using EDI 

Treatment Performance, % removal (avg.) Comments 

Silica > 99.2 

CO2 > 99.5 

Boron > 97.0 Post RO treatment only 

Ammonia > 97.4 

The advantage of EDI is that it doesn’t require addition of chemicals to remove weakly 

ionized species from the produced water. 

ALL Consulting, LLC 24
Evaporation 

Direct treatment of the produced water in an evaporation system eliminates majority of 

chemical/physical treatment. The principle of this technique is to provide latent heat to 

the feed water to generate vapor which can be condensed into pure water form. The 

remaining stream contains high concentration of salts/solids. 

Falling film vertical tube evaporators [16] have the highest heat transfer coefficient which 

is required to save energy. It also minimizes chances of fouling by keeping tubing 

surface wetted during operations. Produced water is de-oiled and pH is adjusted. Next, a 

pre-heater increase the temperature of produced water/brine. Hot brine goes to de-aerator, 

which removes non-condensable gases. Hot de-aerated brine 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 and flows down into each tube through a liquid distributor. 

As the brine flows down the tubes, a small portion evaporates and the rest falls into the 

sump to be recirculated. The vapor travels down the tubes with the brine, and goes to a 

compressor through mist eliminators. Compressed vapor flows to the outside of the heat 

transfer tubes where its latent heat is transferred to the cooler brine slurry falling inside. 

As a result, vapor gets condensed into pure water form which is pumped back through the 

heat exchanger where it gives up sensible heat to the incoming wastewater. A small 

amount of concentrated slurry from the evaporator sump is continuously discarded 

through a blowdown valve to maintain density of the slurry in the evaporator. The 

concentrated blowdown can be disposed through a class I injection well or can be 

converted into solid waste in a crystallizer. 

 Figure 14 – A vertical tube falling film vapor compression evaporator (Source: Ionics Inc.) 

ALL Consulting, LLC 25
Rapid Spray Evaporation (RSE) 

AquaSonics International has developed a Rapid Spray EvaporationTM (RSE) system of 

ejecting contaminated water at high velocities through a specialized injector-nozzle into 

waste heat. The unit uses a heating element for a heat source across which air is blown 

into the evaporation chamber. As the heated air moves along the evaporation chamber, 

nebulized wastewater is injected into the evaporation chamber. The moving vapor and 

brine droplets pass through a mechanical filter which traps the brine droplets. The pure 

vapor phase passes on to a condenser. The brine droplets are periodically flushed from 

the filter with the water being treated. 

As the water vaporizes within milliseconds of ejection, the solids in the solution flash or 

separate out. The water vapor is condensed and collected while the precipitated solids 

form isolated crystalline particles, which are collected through a vacuum process and sold 

as a byproduct. RSE ejects the salt water through a nozzle into a stream of heated air, 

forming a mist of droplets which vaporize almost instantly. The minute flakes of solid 

salt left behind fall to the bottom of the evaporation chamber where they can be collected. 

The best success comes from developing nozzles that allow the process to work with 

hydraulic pressure. 

Applications 

Tests on the RSE system [17] carried out by Westwater Resources Inc, Albuquerque, 

NM, confirmed that it can process water containing up to 16% salt. The operating costs 

for RSE are about one-third of the cost of conventional desalination methods alone, 

producing 1,000 liters of fresh water for between 16 and 27 cents. AquaSonics claims to 

attain nearly 100% salt conversion of salt water into fresh water. Table 9 shows the 

results obtained during the testing phase. 

Table 9 – Rapid Spray Evaporation testing results (Source: WestWater Resource Inc, NM) 

Solute Untreated 

ppm 

Treated 

ppm 

Concentrate 

ppm 

Calcium 79 1.6 20 

Magnesium 490 1.7 600 

Sodium 25,000 160 57,000 

Potassium 610 1.9 1,100 

Chloride 5,000 90 8,400 

Sulfate 31,000 150 35,000 

Bicarbonate 5,700 20 2,900 

Phosphate 1,200 0 - 

Carbon Dioxide 3,100 0 - 

TDS 130,000 440 180,000 

Freeze Thaw Evaporation (FTE) 

Freeze-thaw/evaporation (FTE®) is a process whereby produced water is first stored in a 

holding pond until air temperatures drop below 0° C (32° F). The water is then removed 

from the pond using pumps and sprayed onto a separate freezing pad which consists of an 

ALL Consulting, LLC 26
elevated pipe grid with strategically placed sprinklers. These sprinklers can be raised as 

the ice builds up on the pipe grid. The unfrozen brine water drains from the ice grid and 

is separated using conductivity-controlled valves. 

 

Figure 15 – Spray Freezing FTE unit in operation (Source: Hart Energy Publications) 

The concentrated brine water is then transported to separate storage ponds for either 

secondary treatment or for disposal. Figure 14 shows a picture of Spray Freezing unit 

with sprinklers. The alternate to Spray Freezing process involves allowing the holding 

reservoir to freeze, and draining the brine that forms below the ice. The ice in the pond 

melts in the spring leaving fresh water. 

Applications

Crystal Solutions, LLC, a joint venture of Gas Technology and BC Technologies, utilized 

FTE [18] for produced water treatment at its first major commercial treatment facility 

near Wamsutter, Wyoming. The FTE uses naturally occurring ambient temperature 

swings to alternately freeze and thaw produced water, concentrating the dissolved solids 

and producing fresh water suitable for various beneficial uses. 

During the 1999-2000 cycle, produced water with 14,000 ppm of TDS was converted to a 

concentrated brine of approximately 64,300 ppm TDS and the fresh water (melt from ice) 

having 924 ppm TDS. Roughly 55% of the feed was converted to melt water; about 30% 

is lost to evaporation and/or sublimation; and only about 15% of the original feed remains 

as concentrated brine. In this case, due to the concentrated brine having a potassium 

chloride concentration in excess of 2% it was a usable product for drilling applications. 

ALL Consulting, LLC 27
Pressure Driven Membrane Separation Technologies 

Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF) and Reverse Osmosis 

(RO) utilize high pressure across the membranes to accomplish filtration of contaminants 

from the produced water. These technologies are the most common techniques of water 

purification. The membranes are also continuously being upgraded or modified for 

superior performance. Various applications of the pressure driven membrane 

technologies are listed in Table 10. Molecular Weight Cutoff (MWCO) is the ability of a 

membrane to reject the species of certain molecular weight measured as Daltons. 

Table 10 – Applications of advanced membrane filtration technologies 

Membrane Filtration Separation Specifications Applications/Removal 

Microfiltration (MF) >100,000 Daltons 

10 - 0.1μm 

bacteria, viruses, suspended 

solids etc 

Ultrafiltration (UF) 10,000 to 100,000 Daltons 

0.05 - 5 e-3 μm 

proteins, starch, viruses, colloid 

silica, organics, dyes, fats, paint 

solids etc 

Nanofiltration (NF) 1,000 to 100,000 Daltons 

5 e-3 - 5 e-4 μm 

starch, sugar, pesticides, 

herbicides, divalent ions, 

organics, BOD, COD, detergents 

etc 

Reverse Osmosis (RO) salts and lower MWCO 

1 e-4 - 1 e-5 μm 

metal ions, acids, sugars, aqueous 

salts, dyes, natural resins, 

monovalent salts, BOD, COD, 

ions etc 

Gas Liquid Membrane CO2, H2S 

decarbonation, hydrogen sulfide 

removal 

 

MF, UF and NF are based on the principle of rejection of species higher than the pore 

size of the membrane under pressure. RO uses the operating pressure higher than the 

osmotic pressure of salt present in the water to drive pure water through the membrane, 

thereby rejecting the salts. It is reversal of the osmosis process where water flows from 

the higher concentration solution to the lower concentration solution to attain natural 

equilibrium. The notion of these filtration technologies is discussed in the literature [19]. 

In gas-liquid separation, the pressure difference across a selective membrane is with pore 

size of about 0.03 micrometers (small enough to prevent water from leaking out but large 

enough to allow CO2 to pass through) is applied. Gas penetrates into the membrane at a 

rate that depends on diffusivity and solubility of molecules in order to attain the 

equilibrium between the gas phase and the solute gas in liquid. The pressure difference is 

created by either vacuum or gas sweep through the membrane. 

Oil and gas operators exploit the clear advantages of using mobile produced water 

treatment units. Osmonics Inc, one of the leading manufacturers of membranes focusing 

ALL Consulting, LLC 28
on produced water treatment applications, has been developing high performance 

compact membrane (such as spiral wound membrane) modules [20]. These membrane 

modules are easy to utilize in mobile systems. The spiral wound membrane offers the 

most efficient packing of membrane area to provide higher membrane contact area in 

limited space. The performance of these membranes is reduced by higher temperature; 

the upper limit for operating temperature is 113 to 122°F but some of the spiral wound 

elements it can be used up to 194°F. Higher temperature operations require more 

pressure differential across the membranes and so more energy is required to achieve 

desired separation. However, higher temperature reduces the viscosity of the solution 

which somewhat offsets the temperature effect [21]. The pH of the solution is also an 

important factor during the membrane filtration operations. High pH RO operation 

effectively removes boron if the membrane can sustain high pH. 

Membrane fouling is a common problem in the various membrane filtration processes. 

Higher flow rate through the membrane module can produce enough shears near the 

membrane to avoid accumulation of oil and fouling agents. A hydrophilic membrane is 

less prone to oil fouling as it has a higher affinity for water and ability to reject oil and 

grease. New Logic Research developed vibrating membrane mechanism to avoid 

membrane fouling caused by free oils and scaling agents [22]. The sinusoidal vibration of 

the membrane avoids the migration of colloids onto the membrane surface. The colloids 

are washed away with reject in the cross-flow configuration. The anionic membrane 

repels anions (monovalent, divalent or multivalent) and also associated cations (sodium, 

magnesium, copper, zinc, iron etc.). Figure 15 shows a conceptual picture of Vibratory 

Shear Enhanced Processing (VSEP) membrane. 

 Figure 16 – A VSEP membrane avoids fouling by continuous sinusoidal vibration 

 (Source: New Logic Research Inc) 

Petroleum recovery and research center (PRRC) of New Mexico Institute of Mining and 

Technology has developed inorganic membranes for the produced water treatment 

focusing on the treatment of high salinity produced water (> 50,000 ppm in San Juan and 

> 100,000 ppm in Permian basin). The inorganic membranes made up from zeolite 

provided higher flux, pH compatibility, and thermal and chemical stability. Table 11 

shows the higher removal efficiency, even lower differential pressure and higher flux 

operations. Each row is for different membranes. 

ALL Consulting, LLC 29
Table 11 – Performance of various zeolite membranes (Source: PRRC, NMIMT) 

Membrane Ions in feed TDS, ppm Pressure, psi Flux, 

kg/m2

.h 

Rejection, 

% 

1 Na+, K+, Ca2+, 

Mg2+, NH4

+

, 

Cl39,000 350 0.112 74.5 

2 Na+, Cl- 5,500 300 0.135 89.2 

3 Mg2+, Cl- 9,400 300 0.081 68.6 

4 Ca2+, Cl- 11,000 300 0.096 57.6 

5 Na+, SO4

- 14,200 300 0.097 57.4 

6 Na+, Cl- 5,000 300 0.24 76.8 

Applications 

GE Pilot Study, California: 

In 2001 Osmonics Inc performed a pilot study [23] to evaluate feasibility of membrane 

filtration technologies for the treatment of produced water in northern California near 

Bakersfield. The produced water came to the surface at 185°F with approximately 10,000 

ppm of salt, a high level of suspended solids and free oil. 

The three-step membrane separation combined with an ion exchange step proved to be 

sufficient to yield water suitable for irrigation (< 1,000 ppm TDS). The treated water 

contained 5 to 10 ppm boron which is higher than the 0.75 ppm limit for irrigation water. 

Purification of treated water using Ion Exchange produced boron levels below the 0.75 

ppm limit. The schematic of produced water treatment is shown in Figure 16. 

 Feed Tank 

 pH adjust 

 5.8 – 5.9 

 185°F 

RO, 185°F 

RO, 125°F 

Recycle 

Permeate

Treated Water

Recycle 

12,000 GPD 

From oil/water separator

Cartridge filter

UF, 185°F 

NF, 185°F 

To oil/water separator

Disposal / Reinjection

Figure 17 – GE produced water treatment system, California 

The pH of the produced water from the oil separators was adjusted to 5.8 with sulfuric

acid. The suspended solids were allowed to settle in a tank with a conical bottom. CO2

ALL Consulting, LLC 30
and H2S were degassed from the top of the tank and feed from the middle of the tank is 

discharged to a cartridge filter to remove smaller particles and oil. The effluent from the 

cartridge filter is passed through high temperature UF, NF and RO units followed by 

cooling operation and a low temperature RO unit. The overall system recovery was more 

than 80% considering the recycling of the UF concentrate and the use of the RO 

concentrate for various purposes. Table 12 shows the results of the produced water 

treatment system composed of membrane filtration units.

Table 12 – GE pilot water treatment plant results 

Constituent Feed, ppm UF permeate, 

ppm 

NF permeate, 

ppm 

RO permeate, 

ppm 

Sodium 9,610 9,610 5,250 144 

Calcium 715 715 163 5 

Magnesium 412 412 115 2 

Potassium 174 174 77 2 

Ammonium 110 110 68 2 

Chloride 8,010 8,010 4,710 114 

Sulfate 1,090 1,090 Non-detectable Non-detectable 

Oil 10 – 50 < 1 Non-detectable Non-detectable 

Recovery, % - 90 – 95 % 90 – 95 % 80 – 90 % 

Placerita Canyon Oil Field, California: 

The pilot water treatment unit at Placerita Canyon oil field [24] consisted of warm 

softening, coconut shell filtration, cooling (fin-fan), trickling filter, ion exchange and 

reverse osmosis. The warm softening process removed approximately 95% hardness 

from the produced water. Silica levels in the softening effluent were 80 and 20 mg/l at a 

pH of 8.5 and 9.5, respectively. Silica level decreased to 3 mg/l when 400 mg/l of MgCl2

were added. More than 95% of TDS was removed by RO. Approximately 90% removal 

of boron was achieved at a pH of 10.5 or above. Ammonia removal was 80% at a pH of 

8.7 or below. The capital cost of the treatment varied from $3.4-13.2 million. The annual 

estimated operation and maintenance cost varied from 6 to 27¢/barrel of water treated. 

Table 13 shows the summary of produced water treatment system. Figure 16 shows the 

schematic diagram of the produced water treatment system. 

The first step was the Warm Softening process in which lime, MgCl2 and ionic polymer 

were added to the produced water in order to precipitate calcium and magnesium 

hardness. Equation 6 shows the removal of bicarbonate hardness by addition of lime. 

HCOCa 23 + OHCa 2 → CaCO3 + 22)()( 2OH ..(6) 

ALL Consulting, LLC 31
Table 13– A summary of utilized water treatment processes 

Process Specifications Treatment Comments 

Warm 

softening 

100 gpm throughput with 

10 gpm/ft2

 precipitate 

rising rate 

Hardness, Boron, Silica, 

Ammonia removal 

sodium hydroxide/ polymer

MgCl2 addition 

Cooling Fin-fan heat exchanger cooling effluent from 

softening unit 

necessary to prevent 

damage of the downstream 

units 

Trickling 

filter 

400 ft3

 of polypropylene 

packing 2.5 gpm/ft2

Hydraulic loading 

Biological oxidation of 

organic carbon effluent with < 2 ppm TOC

Ion 

Exchange 

5 ft3

 of Ionac C-249 resin 

with capacity of 25-30 

grains/ft3

Pretreatment to RO 

stage 

residual hardness 

removal 

cation exchange 

membranes 

RO 4 X 40 spiral wound 

membrane 

TDS, Boron, Silica 

removal high pH for Boron removal

GAC 

Adsorber activated carbon packing organics removal post trickling filter 

treatment 

 

 Walnut 

 Shell Filter 

 Warm Lime 

 Softening

 

Fin Fan 

Cooling 

Trickling 

 Filter 

 Pressure 

Ion Exchange Filters 

 

 RO 

Produced Water 

Figure 18 – Schematic of produced water treatment process 

Also boron, silica and ammonia were removed up to some extent in the Lime Softening 

process. The effluent from the softening process was discharged to a fin-fan type heat 

exchanger to cool the water from more than 150°F to just above ambient air temperature 

ALL Consulting, LLC 32
as the units downstream of the softening unit were susceptible to damage at temperatures 

above 100°F. 

The next step was the trickling filter for biological oxidation of organics [25]. Trickling 

filter is a plastic or rock packed system with large diameter to depth ratio. Influent water 

is trickled through from the top in the presence of air (oxygen). The microorganisms in 

the produced water attach on the surface of packed media to form a biological film. 

Subsequently the organic materials get degraded by the biological film. As the biological 

film thickens through microbial growth, oxygen penetration to the packed media is 

affected. Also portions of the film lose their ability as they are used to degrade organics. 

This causes the used layer to fall off from the packed media, known as sloughing process. 

Next the sloughed solids are removed in pressure filters. During most stages of testing, 

the trickling filter was bypassed to allow the microbes produced to acclimate to the water 

organics. When bypassing the trickling filter, the water was sent directly from the heat 

exchanger. 

Next the processed water passed through the ion exchange softeners to remove any 

residual hardness. Finally, RO was used to remove TDS, boron and additional organics. 

The RO permeate was sent to a 2,000-gallon polyethylene tank for storage and the 

concentrated reject stream was sent to the system drain. pH adjustment is the most 

important step in the treatment system because boron, silica, ammonia and harness 

removal depends on pH of the solution. The relationships among the constituents are not 

monotonous which required careful pH adjustment during the process. For example, as 

the pH of the solution increases more silica gets ionized and that increases silica 

solubility, which may increase membrane leakage and deteriorates the silica removal. 

Opposite to that, as the silica solubility increases the chances of membrane fouling due to 

silica precipitation decreases, which improves RO membrane performance. As the pH of 

the solution increases ammonia solubility decreases, which diminishes ammonia removal 

by RO.

High Efficiency Reverse Osmosis (HEROTM) 

Ionics Inc developed HEROTM [26] to provide higher water recovery, higher quality 

permeate, higher operating flux and lower overall cost than conventional RO treatment. 

The most important stage of HERO is pretreatment of the feed water before RO operation 

to raise the pH of feed water which enables higher efficiency. As discussed earlier, 

increase in pH improves boron removal and avoids membrane fouling. 

As shown in Figure 18, HERO is a three step process. 

1. Hardness removal: Calcium and Magnesium harness can precipitate on RO 

membranes at high pH, which causes membrane fouling. Alkali was added to balance 

alkalinity and hardness which improves weak acid cation exchange (WAC) softening 

process efficiency. WAC resins exchange hardness from the produced water as 

discussed earlier. The H+

 addition increase pH that enabled conversion of bicarbonate 

alkalinity into carbon dioxide. 

ALL Consulting, LLC 33
2. Carbon dioxide removal: As discussed in earlier sections, degasification using air 

stripping removes carbon dioxide from the water. The carbon dioxide removal further 

increases pH of the produced water. 

3. High pH RO: High pH water increases solubility of silica and destroys biological 

organisms that cause membrane fouling. Dissolved solids were removed by the RO 

process. 

Weak Acid

Cation 

Exchange

Carbon

Dioxide 

Removal RO 

Alkali (if needed)

Alkali

Acid (if needed)

Permeate

Concentrate 

Figure 19 – A schematic of HERO system developed by Ionics Inc

The biggest advantage of the HERO system is the reduced capital cost (~15%) at higher 

flux rate (50 GPM). Because of reduced fouling and scaling of the RO membrane, the 

operating and energy costs for HERO are also less than conventional RO. The increase in 

water recovery is obvious with HERO systems due to the high performance of 

membrane. The shortcomings of HERO are the treatment chemical requirements and the 

higher costs at lower flux operations. 

Ionics Inc tested a HERO system to upgrade the water purification plant of Sandia 

National Laboratories at Albuquerque, New Mexico. The system produced approximately 

94% water recovery. The reported power usage was approximately 17 kWh per 1000 

gallons of treated water. The reported operating cost was approximately $0.064 per

gallon of treated water. 

Oxidation Reactor 

Newpark Environmental Services offers an innovative treatment system consisting of 

several components and is based on aggressive oxidation followed by precipitation of the 

contaminants present in the produced water [28]. Oxidation of contaminants is the most 

important part which is accomplished in HB Reactor, a proprietary design of Newpark 

Environmental Services. HB Reactor is the part of chemical/physical treatment stage of 

this multi-stage technology. Chemical/physical stage is often adequate to achieve many 

water treatment requirements on its own. Dissolved contaminants such as monovalent 

salts are extremely resistant to oxidation/precipitation and may not be removed during 

chemical/physical treatment stage. Such contaminants can be removed in the 

demineralization stage which consists of MF, UF and/or RO units. The chemical/physical 

treatment stage before the demineralization stage removes contaminants that can plug the 

membrane and improves efficiency of the demineralization stage. 

ALL Consulting, LLC 34
The Newpark system contains three separate stages that can be used separately or in 

tandem: the chemical/physical stage, the demineralization stage, and the waste disposal 

stage. 

Chemical/Physical Stage 

The chemical/physical stage consists of the following elements: 

• Degasification – recovery of methane gas from produced water inflow from CBM 

well and removal of CO2 from produced water. 

• Solids Removal – water from degasification unit is flown through patented Clasiker 

equipment which removes suspended solids ranging from nails to micro fines. 

• pH adjustment – pH of the water is adjusted to neutral as possible which would 

maximize the efficiency of oxidation reactor. 

• Liquid Ring Blower – high volume low pressure air is pumped into the water stream 

just prior to the HB. 

• HB Reactor (sonic oxidation) – the water/air mixture then flows through the reactor 

and is aggressively oxidized/energized. Water/air mixture then enters the reactor 

where millions of small micro-bubbles are generated from the entrained air, by 

mechanical means (5 to 10 psi pressure drop). The micro-bubbles carry positive 

charge and so repel other micro-bubbles but attract negatively charged ions (these 

negatively charged ions are associated with positively charged ions) in the form of a 

contaminant (Ca+

CO3-, Na2

+

SO4

-2 etc.). 

Figure 20 – HB Reactor for aggressive oxidation of contaminants – proprietary design 

(Source: Newpark Environmental Services) 

ALL Consulting, LLC 35
The charged micro-bubbles attract more oppositely charged contaminants and 

become thicker which increases their surface tension continually. Due to ever 

increasing surface tension, the size of the micro-bubble decreases and the pressures 

and temperatures inside the bubble significantly increase, which creates points of 

highly localized temperature. Under the effects of increased pressure and temperature 

contaminants attached to micro-bubbles are violently reacted with O2 associated with 

atmospheric air inside the micro-bubble. The energy associated with this reaction 

results in ultrasonic wave and a very aggressive oxidation of contaminants. Those 

contaminants not oxidized are highly energized and in a very reactive state. The water 

(along with the oxidized and energized ions/contaminants) flows out of the reactor to 

the next stage. 

• Degasser – at this stage all O2 has been consumed but a significant amount of N2 

remains trapped in the water. Degasser removes the trapped N2. 

• Coagulation/Flocculation – a coagulant (lime) and flocculent (anionic polymer) is 

mixed into the water to precipitate out the treated contaminants in the form of 

flocculants. 

• Frictioning – frictioner settles and removes the larger flocculants. 

• High Rate Clarification – a series of tubes settles out and removes the smaller 

flocculants. 

• Sand/Activated Carbon Filtration – the water is then filtered through a sand and 

activated carbon to remove the smallest flocculants. The water becomes clear through 

this process

Demineralization Stage 

Complete removal of dissolved contaminants can be achieved in demineralization stage 

by further treatment of effluent water from chemical/physical treatment system. The 

demineralization stage consists of following elements. 

• MF Unit – sub-micron size particles or contaminants are removed in MF unit. This 

ensures undissolved sub-micron particles do not enter the RO system and plug the 

membranes. 

• RO Unit – the water is then pumped at high pressure through a series of reverse 

osmosis membranes for the concentration and further removal of remaining dissolved 

contaminants. 

Waste Disposal 

Permeate from the RO unit can be utilized as a fresh water source with or without further 

treatment. Concentrate is generally hauled to the nearest disposal facility. Large volumes 

of concentrate, transportation costs, and limited capacity of disposal sites encourage 

further treatment of concentrate. Concentrate can be dried into a solid phase which would 

be easier to handle. 

• Crystalizer and Evaporator – Crystallizer further concentrates the RO concentrate 

stream by extracting water. Total volume of the concentrate is reduced while the 

ALL Consulting, LLC 36
associated TDS increases significantly. The water (extract phase) is re-circulated 

through the RO and concentrate (sludge-water) flows through evaporators. Water gets 

evaporated and the dissolved solids remain in sludge state. Handling and disposal of 

reduced volume of waste in sludge form is easier. 

Figure 21 shows a schematic of produced water treatment system designed by Newpark 

Environmental Services. Newpark has tested this system for the treatment of produced 

water from various sources on the pilot scale. 

Degaser 

CH4 recovery 

CO2 removal 

Clasiker 

SS Removal HB Reactor

Oxidation

Degaser 

N2 removal 

Settler

Frictioning 

Large flocs removal 

Clarifier 

Contaminants removal

Finer flocs removal 

Activated 

Carbon 

Polishing 

stage 

MF RO 

Produced Water

Sludge 

Disposal 

Evaporator 

Stage 1: 

ChemicalPhysical 

Stage 2: 

Demineralization 

Stage 3: 

Waste disposal Crystallizer 

Sludge 

Sludge Sludge 

Concentrate 

Water Recovery 

 Concentrate 

Permeate 

Treated Water 

Air

pH 

Vent

Sludge 

Figure 21 – Produced water treatment system (Source: Newpark Environmental Services) 

ALL Consulting, LLC 37
Table 14 shows the performance of Newpark’s system for the treatment of produced 

water from three facilities. The quality of effluent or treated water at the end of both the 

chemical/physical treatment stage and demineralization stage was supervised. The 

Pinedale and Gillette plants are company-owned facilities that process operators’ water 

on a contract basis. 

 

Table 14 – Results from field test with a produced water treatment system 

Pinedale, WY 

(Pinedale Field 

Produced Water) 

Big Hills, TX 

(Conventional Oil and 

Gas Produced Water) 

Gillette, WY 

(CBNG Water) 

Parameter 

mg/L or ppm Influent 

Effluent 

Influent 

Effluent 

Influent 

Effluent 

Chemical/ 

Physical 

After 

RO 

Chemical/ 

Physical 

After 

RO 

Chemical/ 

Physical 

After 

RO 

Carbonate 

(CO3) < 1 - - < 1 < 1 < 1 < 1 - < 1 

Bicarbonate 

(HCO3) 842 - - 312 156 7.3 2,782 - 12.2 

Calcium 68 - - 2,388 303 0.96 43.67 - 1 

Chloride 4,589 - 56.5 70,978 8,922 355 115 - 18 

Magnesium 9 - - 90 93 0.3 32.87 - < 0.1 

Sodium 3,324 - 36.6 49,590 5,140 217 1,076 - 21.5 

Sulfates 1 - - 6 280 < 1 < 1 - <0.1 

Alkalinity as 

CaCO3

582 - - 210 118 6 2,110 - 10 

TDS 11,957 3,004 93 174,452 19,053 93.1 3,203 1,358 46 

TPH 5 - - 8 2 1 1 - 1 

(Source: Newpark Environmental Services) 

NORM Treatment 

Naturally occurring radioactive materials (NORM) such as radium get mobilized from 

the oil or gas formations because of the solubility in the presence of chloride ions which 

are present in the water within formation [29]. The solubility of radionuclide is very low 

in sulfate species. The low solubility precipitates scale containing high concentrations of 

radium in the form of barium sulfate or barite [Equation 7] under the effects of varying 

temperature and pressure during the production operations. 

4 4 →++ ][ SORaBaSORaBa + + − ..(7) 

The handling and treatment of the precipitated sulfate deposits containing decaying 

radioactive materials is absolute necessity because of the dangers of radioactivity. BPF 

Inc., Texas [30], developed mobile automated treatment includes separation of NORM 

ALL Consulting, LLC 38
solids from other oil field waste (produced water) containing less than 30 pCi/g 

(Picocuries per gram, a measurement of radioactivity) radium and dissolving it into 

aqueous solutions. Extraction of radionuclide from the scales is done by dissolving the 

radioactive material in one or more aqueous solvents in the hydroclone which separates 

solids with no NORM from the solution. The NORM containing solution is transported to 

class II injection site and reinjected into the formation. 

Radioactive materials also occur in natural gas in the form of radon. One of the methods 

to treat the gas is packed bed adsorption of radon with activated charcoal. Monitoring of 

radioactivity is an essential part of NORM treatment which is accomplished by in-situ 

radio-assay capability. 

ALL Consulting, LLC 39
Handling of Water Treatment Waste/Concentrate 

Produced water treatment technologies convert poor quality produced water into 

good quality water by removing contaminants and impurities. As discussed earlier, many 

of such treatment technologies decontaminate inlet produced water producing a waste 

stream with higher concentration of contaminants and a treated water stream. For 

example, membrane systems separate influent water into cleaner product water and a 

more concentrated stream that is called concentrate in RO, NF, and EDR systems and 

backwash in UF and MF systems. Considering large scale of produced water treatment, 

the amount of concentrated waste volume needs to be considered when planning water 

treatment facilities. 

The selection of concentrate disposal practice depends on several factors such as regional 

disposal availability (geology, geographical. climate etc), local availability (existence of 

suitable disposal site, distance, compatibility etc), volume of concentrate stream, 

applicable environmental regulations (NPDES, underground injection control regulations, 

and underground water resource regulations etc. are imposed by local, state or federal 

agencies), environmental impacts, public reception, cost, etc. Along with cost 

contributing factors such as transportation, treatment, development of disposal site, etc; 

environmental regulations also have major impact on the feasibility of any particular 

concentrate disposal method. 

Disposal to surface water: 

Membrane wastes may be discharged to surface waters and ultimately reside within large 

receiving water bodies. Direct discharge to water bodies must have an NPDES permit 

(states authority) which requires meeting CWA regulations for effluent limitations. Large 

volumes of concentrate waste and level of contaminants in it are some of the limiting 

factors for this practice. 

Disposal to sewer: 

NPDES permit is not required for the disposal into publicly owned treatment works 

(POTWs). However, POTWs may enforce pre-treatment before disposal according to 

federal regulations to control the level of wastewater pollutants entering the sewage 

system. 

Disposal with injection well: 

Injection of concentrated waste through a Class I injection well beneath the lowermost 

underground source of drinking water requires meeting UIC regulations according to 

state and federal standards. Research is being attempted to evaluate disposal of 

concentrate into depleted oil or gas fields through Class I well [31]. Formation damage, 

scaling, etc., are some of the concerns for using depleted oil or gas fields. 

Evaporation ponds: 

Evaporation ponds utilize solar energy to evaporate water into atmosphere in vapor form 

leaving behind solids/salts in sludge form. This technology is limited to regions where 

ALL Consulting, LLC 40
solar irradiation is high which results in higher evaporation rate. Permits may be required 

if potential of leakage into surface water or drinking water aquifer exists. 

Spray evaporation: 

An NPDES permit may be required for spray evaporation if the potential of waste runoff 

to a receiving water body exists. 

Zero liquid discharge: 

The objective of zero liquid discharge is to eliminate any liquid waste at the end of the 

water treatment. Evaporators or concentrators can be utilized to concentrate waste stream. 

Conversion of concentrated sludge into solids/salts form can be accomplished by using 

crystallizer. Disposal of solid waste from crystallizer must avoid contamination of surface 

or groundwater. 

ALL Consulting, LLC 41
Summary 

Advantages, Disadvantages, and Applicability 

 Treatment technologies are summarized in the following table that describes 

advantages and disadvantages and ranges of field applicability. Within each objective (for 

example “De-oiling”), technologies can be compared in terms of their advantages, 

disadvantages, resulting waste stream, and applications to oil and gas fields. Advantages 

and disadvantages are described in comparative terms rather than absolute figures that are 

subject to change; the aim is to compare technological options for a given objective. 

Durability and cost are important factors that will depend on site-specific conditions and 

the specific commercial version picked by the operator. Comparisons of inherent 

durability can be made within each objective but these are only generalizations. No 

attempt was made to ascribe economic factors to these technologies since costs will vary 

from location to location and may be dependent upon commercial configurations and 

innovations. 

Waste products are specific to each technology; for example desalinization can result in a 

residue consisting of 20% of the input stream or a residue made up of 1% of the input. 

The 1% residue will be a more concentrated brine than the 20% residue, however, both 

may no longer be classified as oil and gas wastes. Produced water can usually be 

disposed of by way of an exemption from standard industrial waste regulations under the 

federal Resource Conservation and Recovery Act (RCRA). The oil and gas exemption 

means that produced water can be sent to deep disposal wells that inject the water back 

into deep, salt water bearing reservoirs with minimal regulatory requirements and cost. 

Industrial brines are subject to increased regulatory compliance costs. 

Applications might include specific oil and gas operations as well as general producing 

situations. Applications include the treatment objective and the desired beneficial use or 

disposal route being employed. Geological and hydrologic settings for common oil and 

gas fields are also part of the description of certain applications. 

ALL Consulting, LLC 42
Treatment Description Advantages Disadvantages Waste 

Stream 

Oil and Gas 

Produced Water 

Applications 

De-oiling 

Corrugated plate 

separator 

separation of free oil 

from water under gravity 

effects enhanced by 

flocculation on the 

surface of corrugated 

plates 

No energy required, 

cheaper, effective for 

bulk oil removal and 

suspended solid 

removal, with no 

moving parts, this 

technology is robust 

and resistant to 

breakdowns in the 

field. 

inefficient for fine oil 

particles, 

requirement of high 

retention time, 

maintenance 

suspended 

particles slurry at 

the bottom of the 

separator 

Oil recovery from 

emulsions or water 

with high oil content 

prior to discharge. 

Produced water from 

water-drive reservoirs 

and water flood 

production are most 

likely feed-stocks. 

Water may contain oil 

& grease in excess of 

1000 mg/L. 

Centrifuge 

separation of free oil 

from water under 

centrifugal force 

generated by spinning the 

centrifuge cylinder 

efficient removal of 

smaller oil particles 

and suspended 

solids, lesser 

retention time-high 

throughput 

energy requirement 

for spinning, high 

maintenance cost suspended 

particles slurry 

as pre-treatment 

waste 

Hydroclone 

free oil separation under 

centrifugal force 

generated by pressurized 

tangential input of 

influent stream 

compact modules, 

higher efficiency and 

throughput for 

smaller oil particles 

energy requirement 

to pressurize inlet, no 

solid separation, 

fouling, higher 

maintenance cost 

Gas floatation 

oil particles attach to 

induced gas bubbles and 

float to the surface 

no moving parts, 

higher efficiency due 

to coalescence, easy 

operation, robust and 

durable 

generation of large 

amount of air, 

retention time for 

separation, skim 

volume 

skim off volume, 

lumps of oil 

Extraction 

removal of free or 

dissolved oil soluble in 

lighter hydrocarbon 

solvent 

no energy required, 

easy operation, 

removes dissolved 

oil 

use of solvent, 

extract handling, 

regeneration of 

solvent 

solvent 

regeneration 

waste 

Oil removal from water 

with low oil and grease 

content (< 1000 mg/L) 

or removal of trace 

quantities of oil and 

grease prior to 

membrane processing. 

Oil reservoirs and 

thermogenic natural 

gas reservoirs usually 

contain trace amounts 

of liquid hydrocarbons. 

Biogenic natural gas 

such as CBNG may 

contain no liquids in 

the reservoir but when 

pumped to the surface, 

the water takes up 

lubricating fluids from 

the pumps. 

Ozone/hydrogen 

peroxide/oxygen 

strong oxidizers oxidize 

soluble contaminant and 

remove them as 

precipitate 

easy operation, 

efficient for primary 

treatment of soluble 

constituents 

on-site supply of 

oxidizer, separation 

of precipitate, 

byproduct CO2 etc. 

solids 

precipitated in 

slurry form 

Adsorption 

porous media adsorbs 

contaminants from the 

influent stream 

compact packed bed 

modules, cheaper, 

efficient 

high retention time, 

less efficient at 

higher feed 

concentration 

used adsorbent 

media, 

regeneration 

waste 

ALL Consulting, LLC 43
Treatment Description Advantages Disadvantages Waste 

Stream 

Oil and Gas 

Produced Water 

Applications 

Disinfection 

UV light/ozone 

passing UV light or 

ozone produce hydroxyl 

ions that kills microbial 

simple and clean 

operation, highly 

efficient disinfection

on-site supply of 

ozone, other 

contaminants reduce 

efficiency small volumes of 

suspended 

particles at the 

end of the 

treatment 

Microbes may exist in 

the subsurface 

reservoir or can be 

introduced during 

production or during 

water treatments. 

Disinfection may need 

to be done to protect 

potability or to or to 

prevent fouling of the 

reservoir, tubulars, and 

surface equipment. 

Chlorination 

chlorine reacts with water 

to produce hypochlorous 

acid which kills microbial 

cheaper and the 

simplest method 

does not remove all 

types of microbial 

Desalinization 

Lime softening 

addition of lime to 

remove carbonate, 

bicarbonate etc. hardness 

cheaper, accessible, 

can be modified 

chemical addition, 

post treatment 

necessary 

used chemical 

and precipitated 

waste 

These technologies 

typically require less 

power and less pretreatment than 

membrane 

technologies. Suitable 

produced waters will 

have TDS values 

between 10,000 and 

1,000 mg/L. Some of 

the treatments remove 

oil and grease 

contaminants and some 

of them require oil and 

grease contaminants to 

be treated before these 

operations. 

Ion exchange 

dissolved salts or 

minerals are ionized and 

removed by exchanging 

ions with ion exchangers 

low energy required, 

possible continuous 

regeneration of resin, 

efficient, mobile 

treatment possible 

pre and post 

treatment require for 

high efficiency, 

produce effluent 

concentrate 

regeneration 

chemicals 

Electrodialysis 

ionized salts attract and 

approach to oppositely 

charged electrodes 

passing through ion 

exchange membranes 

clean technology, no 

chemical addition, 

mobile treatment 

possible, less 

pretreatment 

less efficient with 

high concentration 

influent, require 

membrane 

regeneration 

regeneration 

waste 

Electrodeionization 

enhanced electrodialysis 

due to presence of ion 

exchange resins between 

ion exchange membranes 

removes of weakly 

ionized species, high 

removal rate, mobile 

treatment possible 

regeneration of ion 

exchange resins, 

pre/post treatment 

necessary 

regeneration 

waste, filtrate 

waste from posttreatment stage 

Capacitive 

deionization 

ionized salts are adsorbed 

by the oppositely charged 

electrodes 

low energy required, 

higher throughput 

expensive electrodes, 

fouling 

regeneration 

waste 

Electrochemical 

Activation 

ionized water reacts with 

ionized chloride ion to 

produce chlorite that kills 

microbial 

simultaneously salt 

and microbial 

removal, reduce 

fouling 

expensive electrodes regeneration 

waste 

Rapid spray 

evaporation 

injecting water at high 

velocity in heated air 

evaporates the water 

which can be condensed 

to obtained treated water 

high quality treated 

water, higher 

conversion efficiency

high energy required 

for heating air, 

required handling of 

solids 

waste in sludge 

form at the end 

of evaporation 

ALL Consulting, LLC 44
Treatment Description Advantages Disadvantages Waste 

Stream 

Oil and Gas 

Produced Water 

Applications 

Freeze thaw 

evaporation 

utilize natural 

temperature cycles to 

freeze water into crystals 

from contaminated water 

and thaw crystals to 

produce pure water 

no energy required, 

natural process, 

cheaper 

lower conversion 

efficiency, long 

operation cycle 

Membrane Treatment 

Microfiltration 

membrane removes 

micro-particles from the 

water under the applied 

pressure 

higher recovery of 

fresh water, compact 

modules 

high energy required, 

less efficiency for 

divalent, monovalent 

salts, viruses etc. 

concentrated 

waste from 

membrane 

backwash during 

membrane 

cleaning, 

concentrate 

stream from the 

filtration 

operation 

Removal of trace oil 

and grease, microbial, 

soluble organics, 

divalent salts, acids, 

and trace solids. . 

Contaminants can be 

targeted by the 

selection of the 

membrane. The size 

distribution of the 

removable species for 

membrane filtration 

technologies is shown 

in table 9. 

Ultrafiltration 

membrane removes ultraparticles from the water 

under the applied 

pressure 

higher recovery of 

fresh water, compact 

modules, viruses and 

organics etc. removal

high energy, 

membrane fouling, 

low MW organics, 

salts etc 

Nanofiltration 

membrane separation 

technology removes 

species ranging between 

ultrafiltration and RO 

low MW organics 

removal, hardness 

removal, divalent 

salts removal, 

compact module 

high energy required, 

less efficient for 

monovalent salts and 

lower MW organics, 

membrane fouling 

Reverse 

Osmosis 

pure water is squeezed 

from contaminated water 

under pressure 

differential 

removes monovalent 

salts, dissolved 

contaminants etc., 

compact modules 

high pressure 

requirements, even 

trace amounts of oil 

& grease can cause 

membrane fouling 

Removal of sodium 

chloride, other 

monovalent salts, and 

other organics. Some 

organic species may 

require pre-treatment. 

While energy costs 

increase with higher 

TDS, RO is able to 

efficiently remove salts 

in excess of 10,000 

mg/L. 

Miscellaneous Treatment 

Trickling Filter 

develops film of 

microbial on the surface 

of packed material to 

degrade contaminants 

within water 

cheaper, simple and 

clean technology 

oxygen requirement, 

large dimensions of 

the filter 

sludge waste at 

the end of the 

treatment 

Removal of suspended 

and trace solids, 

ammonia, boron, 

metals etc. Posttreatment is normally 

required to separate 

biomass, precipitated 

solids, dissolved gases 

etc. 

Constructed 

wetland 

treatment 

natural oxidation and 

decomposition of 

contaminants by flora and 

fauna 

cheaper, efficient 

removal of dissolved 

and suspended 

contaminants 

retention time 

requirement, 

maintenance, 

temperature and pH 

effects 

SAR adjustment addition of Ca or Mg ions cheaper option chemical addition 

Balance high SAR and 

very low TDS (higher 

percentage of sodium 

salts) after membrane 

processes. 

ALL Consulting, LLC 45
Treatment Description Advantages Disadvantages Waste 

Stream 

Oil and Gas 

Produced Water 

Applications 

NORM Treatment 

NORM 

treatment 

extraction of radioactive 

material with aqueous 

solution 

efficient for reducing 

radioactive waste 

volume 

extracted radioactive 

materials need 

further treatment or 

disposal 

Produced waters 

containing high levels 

of Uranium or 

Thorium. Unless 

treatment is 

accomplished, 

radioactive scale can 

form in surface 

equipment extensive 

remediation. 

Natural Gas Recovery 

Air stripping stripping of dissolved gas 

from water 

concurrent or 

countercurrent 

operations, cheaper 

post treatment, lower 

efficiency 

Ranking 

The effectiveness and performance of the various treatment technologies can also be 

analyzed according to a new five-step ranking approach devised by the authors and 

described in this section. Rankings can best be used to select between technologies based 

on a carefully defined set of criteria. Rankings will need to be updated as 

commercialized technologies will change and as innovations are installed and made 

newly available. The ranking of each step depends on the rankings of other steps. 

Reasonable engineering judgment and experience assists in utilizing this ranking 

criterion. The following is an example of a ranking scheme for treatment technologies as 

they apply to the treatment and management of produced water. It should be noted that 

the rankings that follow are subjective, are the product of the authors, and are subject to 

change. 

Step 1 – Ability to remove technology specific contaminants: 

 The simplest method to express the performance of a treatment technology is the 

removal of contaminants in percentage. Ranking can be assigned in five categories: 

Removal of contaminants, % Rank 

>95 5 

90-95 4 

75-90 3 

50-75 2 

< 50 1 

ALL Consulting, LLC 46
Step 2 – Consumption of resources to achieve desire removal using given technologies: 

 The consumption of resources in terms of effort, cost, energy, natural resources, 

etc. must be considered in ranking. As stated earlier regarding the interdependency of 

ranking criteria, in the case of RO operation, higher pressure across the membrane 

(energy) is required to achieve higher removal of salts at higher recovery rate. The 

ranking is thought to be assigned as: 

Level of resources consumption Rank 

low 5 

moderately low 4 

moderate 3 

high 2 

very high 1 

Continuing discussion of RO, 75-90% [rank 3] removal of dissolved salts requires 

moderate energy [rank 3]. For the same membrane and contaminants level >95% [rank 

5] removal requires high energy [rank 2]. 

Step 3 – Requirement of pre- or post-treatment technologies with given technologies: 

 Most of the treatment technologies require pre- or post-treatments to improve 

efficiency, to achieve better quality, to handle byproducts, etc. The extent of such 

requirements significantly contributes to the overall performance but also adds to cost, 

facilities, and technological complexity. Ranking assigned in five categories is: 

Pre/Post treatment requirement Rank 

Basic: cooling, heating, settling, impoundment, 

etc. 

5 

Primary: pH adjustment, softening, chemical 

addition, de-oiling, suspended solid removal, sand 

filtration, etc. + technologies in previous section 

4 

Secondary: soluble hydrocarbons removal, GAC, 

dissolved gas removal, biological treatments, 

disinfection, etc. + technologies in previous 

sections 

3 

Moderate: regeneration, fouling prevention, 

trickling filter, constructed wetland, ionization and 

removal, UF or NF, low pressure RO, etc. 

+ technologies in previous sections 

2 

Significant: high pressure filtration, high pressure 

RO, NORM treatment, etc. + technologies in 

previous sections 

1 

Step 4 – Durability of the treatment technology: 

Some technologies rely on automated activation of pumps and valves to move 

fluid while other technologies feature simpler flow paths that are gravity-driven. Simpler 

ALL Consulting, LLC 47
technologies are easier to maintain and cheaper to operate. This factor analyzes the 

degree of durability within a technology. 

Durability Factor Rank 

Inlet water driven by gravity, no 

moving parts, facility not prone to 

fouling and scaling, maintenance by 

schedule or automated warning 

4 

Simple automated pumping cycles and 

few adjustments needed. 

3 

Complex automated cycles needing 

occasional adjustment and repair. 

2 

Operator onsite at all times makes 

adjustments and repairs during 

process. 

1 

Step 5 – Mobility of the treatment units: 

 The compatibility of treatment technologies to be performed as mobile units 

benefits the produced water treatment and adds flexibility during oil and gas operations. 

If the treatment units are self-contained and mobile, the operator can change locations as 

water production changes within the field. Many of the individual technologies can be 

performed by mobile units. However, they may require pre- or post-treatments which can 

only be performed by fixed units. Such operations are categorized as partially mobile 

treatments in the following ranking; 

Mobility of treatment technologies Rank 

Fully mobile 2 

Partially mobile 1.5 

Fixed 1 

Good quality produced water from oil or gas formations may require minimum polishing 

treatments which can be accomplished by compact modules of GAC and RO operated on 

a mobile treatment truck. Such treatments are fully mobile [rank 2]. 

Step 6 – Level of contaminants in influent produced water: 

 The quality of influent produced water also contributes to the overall performance 

of treatment technologies. This can be ranked as: 

Level of contaminants Rank 

Low: suspended solids, moderate 

concentration of free or dispersed oil, low 

hardness level, easily removable gases etc. 

TDS: < 5,000 ppm 

TOC, TPH: < 30 ppm 

5 

ALL Consulting, LLC 48
Medium: ammonia, boron, hardness ions, 

BTEX, dissolved gases, fine oil particles, 

metal ions etc. 

TDS: 5,000-10,000 ppm 

TOC, TPH: >30-100 ppm 

+ contaminants in next section 

4 

High: hydrogen sulfide, heavy metals, 

weak ions, NORM, monovalent salts, trace 

soluble organics etc. 

TDS > 10,000-35,000 ppm 

TOC, TPH > 100 ppm 

+ contaminants in next sections 

3 

Final Step – Calculation of overall rank based on above ranking criteria: 

 After estimating ranks of each five steps, the final formula as described below 

calculates overall rank. The possible highest rank is 7 and the least possible rank is 1. On 

the scale of 7, the treatment technologies with higher rank confirm better performance, 

economics and flexibility. The overall ranking formula is: 

[ ] ( )

6.

5.4.3.2.1.

step

+ + + + stepstepstepstepstep

For example, considering treatment of a good quality produced water [step 6, rank 5] 

with low pressure RO [step 2, rank 4]. The secondary pretreatments [step 3, rank 3] 

would be sufficient in this case to achieve >95% removal [step 1, rank 5] of 

contaminants. This treatment can be operated with a fully mobile unit [step 5, rank 2]. 

The RO system may need attention of operator all the time [step 4, rank 1]. According to 

the formula the overall rank on a scale of 10 is: (5 + 4 + 3+1+ 2) / 5 = 3 (out of 7). 

The formula is sensitive up to two decimal points. Even the difference of 0.05 can be 

significant. The following table compares performance of HEROTM (high efficiency RO) 

and HEEDTM (high efficiency ED) technologies discussed in earlier sections. 

Criteria HERO HEED 

Step 1: Removal efficiency 5 4 

Step 2: Resources consumption 3 4 

Step 3: Pre/post treatment requirement 3 2 

Step 4: Durability of system 1 1 

Step 5: Mobility of treatment 2 2 

Step 6: Level of contaminants in feed 3 3 

Overall Rank 4.667 4.333 

The results indicate better performance with HEROTM system and highlight that system’s 

higher efficiency in spite of requiring more resources. This ranking was made on the 

basis of individual, historical experience with these two systems and is in no way meant 

as an endorsement or widespread judgment of either system. It is meant as an illustration 

ALL Consulting, LLC 49
of the ranking mechanism. This ranking scheme can be applied to a range of 

technological options for treating produced waters. The ranking can help the oil and gas 

operator choose between options, but of course an important part of the decision will 

depend on the requirements for the chosen end use for the water. 

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