### 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 wa ter treatment include meeting discharge regulations (local, state and federal), reusing treated pr oduced water in oil and gas operations, developing agricultural water us es, rangeland restoration, cattle and animal drinking water, water for human consumpti on, and meeting water quality requirements for miscellaneous beneficial uses. Curre nt 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, ha ve 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 Departme nt 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 a nd 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 c onsidered 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 c ould adversely affect the life of the well, thereby leaving substantial re coverable reserves in the ground. Produced water handling practices must also be environmentally protec tive or the operator could face regulatory action. Produced water handling methodology depends on the composition of produced water, location, quantity and th e 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 fractur es or Downhole Water Separa tors which separate water from oil or gas streams downhole and reinject it in to 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 injectat e to reduce fouling and scaling agents and bacteria might be necessary. While waste wa ter 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 pr oduced 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, s timulation, and workover operations.

5. Consume in beneficial use – In some cases, significant treatment of pr oduced water is required to meet the quality required for be neficial 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 f acilitate additional water management options for operators such as beneficial uses that in the short and long term can potentially provide certain community and economic a dvantages. Treated produced water has the potential to be a valuable pr oduct rather than a waste. The treatment of produced water is a necessity before the majority of the conve ntional produced waters can be applied to

ALL Consulting, LLC 2other uses. The general objectives for operators when they plan produced water treatment

are:

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

2. Soluble organics removal – Removal of dissolved organics.

3. Disinfection – Removal of bacteria, micr oorganisms, algae, etc.

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

5. Dissolved gas removal – Removal of light hydro carbon 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 so dicity levels prior to irrigation.

9. Miscellaneous – Naturally occurring radioac tive materials (NORM) removal.

Selection of produced water treatment structur e 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 achie vement 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 objec tives 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 petr oleum industry; it is more often than not only a cost that must be c ontrolled to enhance project economics. Water management and cost control can be done by choosing appropriate wa ter disposal options or by finding an appropriate beneficial use fo r the water. Waste options and beneficial uses are, however, highly dependent upon wa ter quality and may re quire water treatment prior to disposal or use. Tr eatment of produced water may be required in order to meet pre-disposal regulatory limits or to meet bene ficial use specifications . If the oil and gas operator aims to utilize a low-cost disposal op tion 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 Sodi um 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 wi shes to convey his produced wa ter 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. Pr oduced 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 (sma ll oil droplets), and emulsified oil. Oil and grease discharge, along with produced water, involves compliance with stringent regulations. For example, mont hly average oil content of 29 ppm (analyzed by EPA 1664 A) in dischargeable produced wate r 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.

ALL Consulting, LLC 4Table 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 flocculant s 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 requ ires higher capital, maintenance and cleaning costs.

Corrugated plates are packed to enhance th e performance of grav ity separation tanks (Figure 1). The oil droplets co alesce and form larger oil drop lets 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 o il more rapidly from the produced water. The density of oil partic les reduce as they attach to ga s 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 ai r 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 provi des 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 floa tation system have been developed which use 5-50 micrometer bubbles through the reactor [3] . Smaller bubbles more effectively separate oil from the produced water whic h results in low skim volume (Figure 3).

ALL Consulting, LLC 5Figure 1 – Corrugated Plate (CPI) packing separates oil and solids from produced water (Source: NATCO Group)

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

ALL Consulting, LLC 6Figure 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 e nd. The improved gravity effect provides a higher rate of separation. The o il removal efficiency is higher with multi-cone (Figure 4)

ALL Consulting, LLC 7modules that achieve small installation foot prints. The devices are easily accessible and work even with high oil concentrations. Th e 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 re move suspended solid. It handles solid particles as small as 2 microns. The disadva ntages of centrifuges include low throughput and high maintenance costs.

Macroporous polymer extraction (MPPE) treatm ent 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 solv ent extracts disperse d oil and polycyclic aromatics from the contacting produced water stream [4] . In-situ generation of extraction liquid is accomplished by periodically stri pping 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 a ttempted by some oil and gas producers. Extraction enables enhanced removal of disp ersed oil by coalescing small oil droplets during the process [5]. This process utilizes the principl e of higher solubility of heavier hydrocarbons in lighter hydrocarbons.

Adsorption is a widely accepted technology fo r 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 c ontains little or no hydrocarbon s. Highly porous adsorbents with higher surface area o ffer better performance. Acti vated carbon, nutshell media, modified organoclay, etc. are so me 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 contaminan ts (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 al so 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 disinf ect the water. Advanced oxidation processes involving a combination of UV light and ozone or hydrogen peroxide have also been attempted. Oxidation is able to redu ce chemical oxygen demand (COD), biological oxygen demand (BOD), organics, iron, nitrite, manganese, cyanides, pesticides, hydrogen sulfide and aromatic hydrocarbons. Biologi cal decomposition (combined oxidation and reduction) of produced water in a constructe d wetland is also useful for treating raw produced water and treating post-treatment wate r after it has been th rough other treatment

ALL Consulting, LLC 8processes. Plants and microorganisms ar e 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 an d 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 rem ove 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 treatme nts. Advanced filtration techniques are one of the effective techno logies used to remove microorganisms. UV light treatment, chorine or iodine reacti on, ozone treatment and pH reduction are other treatments available to disi nfect produced water. Some of the general and advanced disinfection treatments are disc ussed in the next section.



### Miscellaneous Treatment Produced water softening, SAR adjustments and removal of trace contaminants, pollutants, naturally occurri ng 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 addresse d by treatment technology options. The options can differ in their inherent facility requirements, capital costs, operating expense, and waste streams; all three fa ctors can be important to the oil and gas operator. Some technologies may have large sp ace 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 insta llations where a large amount of dedicated equipment must be purchased just for managi ng produced water. Higher power costs and chemical expenses could be unsupportabl e early in th e life of an oil and gas development. Treatment wastes derive d 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 te sted 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 atmospheri cally 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. Th e final stage contained granular activated carbon (GAC). The samples of inlet feed, efflue nt from ET #1 columns and effluent from the GAC column were analyzed by a sta ndard EPA (EPA 1664-A) analytical testing method.

Figure 5 – A mobile packed bed adsorption system fo r the treatment of produ ced water (Source: ET Ventures Inc)

ALL Consulting, LLC 10Figure 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 obtain ed 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 averag e 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 f ilm bioreactors that utilize va rious species of plants and microbes along with sands that oxidize contaminan ts present in the wa ter. A schematic of treatment process is shown in Figure 6.

C ool i n g T o wer C ool i n g Trenc h Net t e d P o nd

Wetlan d C ool i n g Trenc h

Creek Ox i d atio n

Figure 6 – D O E Na val Pet r ol eum R e serve’s bi o

- t r eat m e nt pr ocess
The process undergoes the following steps:

1. Cooling to wer f o llowed by a shallow cooling trench to r e duce the te mperature o f produced water from 180 – 200°F to belo w 100°F. Higher tem p eratures reduce the perform a nce of plants in the subsequent wetland pond.

ALL Consul ting, LLC 112. Netted pond or skimming pond further cooled the water and also removed suspended solid and oil under gravity effects. Disper sed oil on the top surface was skimmed off.

3. Specially developed flora and fauna in cluding 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 mo st of the hydrocarbons and the remaining traces of hydrocarbons are rem oved in an oxidation process.

The produced water from the Tensleep form ation 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 or ganics, 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 Aft er treatment, ppm Overall removal, %
NH 3 2.03 0.54 73 NO 3 <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 remove s arsenic, heavy metals, nitrates, radium, salts, uranium, and other elements from the prod uced water. Ion exchange is a reversible chemical reaction wherein positively or negati vely charged ions present in the water are replaced by similarly ch arged ions present within the re sin. The resins immersed in the water are either naturally occu rring inorganic zeolites or synthetically produced organic resins. When the replacement ions on the resi n are exhausted, the resi n is recharged with more replacement ions.

ALL Consulting, LLC 12Ion Exchange Resins Ion exchange resins are classified as cation exchangers, which exchange positively charged ions and anion exchangers, which exch ange negatively charged ions. The resins are further classified as:

Strong Acid Cation (SAC) Resins : The hydrogen or sodium forms of the cati on 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.

HClNiSORNiClHSOR 2)( )(2 4 2 3 +

− →+− ..(1)

Equation 2 shows an example of Ca + softening with SAC.

+ + +−→+− HCaSORCaHSOR 2)()(2 2 3 3 ..(2)

These resins would be used in the hydrogen form for comple te deionization (Na, Ca, Mg, Ba, etc. removal); they are used in the so dium form for water softening (Ca and Mg removal). After exhaustion, the resin is rege nerated 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 (SO 3 H) used in strong acid resi ns. These resins behave sim ilarly to weak organic acids that are weakly dissociated. WAC has high affi nity for divalent salts. Equation 3 shows an example of Ca + softening with WAC. Alkalinity pres ent in bicarbonate form can also be removed by WAC.

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

Free H + ions can react with bicarbonate (present as hardness, Ca(HCO 3 ) 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.

OHCOCOHHHCO 22 32 3 +→ →+ +
− ..(4)

Weak acid resins exhibit a much higher affi nity for hydrogen ions compare to strong acid resins. This characteristic allows regeneration to the hydr ogen form with significantly less acid than is required fo r 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. C onsequently, resin capacity depends in part on solution pH.

ALL Consulting, LLC 13Strong 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 deionizati on. 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.

HOHClNHRHClOHNHR +

− →+

− ) () ( 3 3 . .(5)

Regeneration with concentrated sodium hydr oxide (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 Pr oject Plan of Development (POD) [9] to drill and test for coal bed natural gas ( CBNG) in eight federa l 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-c urrent 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 surrounde d by a shallow spill contai nment 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 th e Higgins Loop. Removal of CO 2 produced during the ion exchange process and adjustment of pH will be achieved by adding calcium hydroxide. CO 2 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 Hi ggins Loop is a verti cal cylindrical loop containing a packed bed of strong acid ion exchange resin that is separated into four

ALL Consulting, LLC 14operating zones by butterfly (loop) valves . These operating zones (Adsorption, Regeneration, Backwashing and Pulsing) function like four se parate 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 re spective zone and repl aced 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 resi n in the regeneration zone concurrent with ion exchange in the adsorpti on zone. Dilute hydrochlor ic acid is injected into the loop and moves count er-current to the resin and the spent brine discharge, leaving the resin restored to the hydronium form.

Concentrated brine volumes average approxima tely 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 othe r beneficial uses is proposed to be transported of fsite by truck for disposal injection into a permitted Class I, de ep 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.

ALL Consulting, LLC 15Figure 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 (SO 3 H + ) group that exchanges Na + , Ba + , Ca 2+

, 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 Ri ver 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

ALL Consulting, LLC 16The 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 pe r barrel of treated water depending on the influent composition, SAR, and availability of resources. The ion ex change treated water may then be discharged to the envi ronment 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 stabili ty over a large rang e of pH. Based on the results of various experiments, SNL repor ted average ion exchange capacity of HTC and Permutite as 2.5 mEq/gram (measured with Na 2 So 4 ), and 1.7-2.7 mEq/gram (measured with NaOH) respectively.

Water i n Lim e in HTC in Perm u tite in

Treated
water ou t UF

HTC
rege nerat i on/ di spo s al Perm u tite
rege nerat i on/ di spo s al

Figure 9 – Ion Ex ch an g e /So r p tio n d e salin atio n pro cess (Sou rce: SNL)

Anions in the inlet water are replaced by hydroxide ions (HTC anion exchange) and cation s are replaced by hydrogen io ns (Perm u tite cation exchange). Lime softening pretrea tm ent is optiona l sta g e.

Ion exch ang e rs are regenerated after they ar e exhausted. In the re generation process ion exchangers regain their ion ex change capacity. It m a y not be possible to regain 100% ion exchange capacity dur ing regeneration proces s. SNL attem p ted to de ter m ine ef f

ects of regeneration on the ion exchange capacity of above m e ntioned ion exchangers and concluded that Perm utite can regain ion exch ange capacity without significan t loss. Regeneration of HTC at low tem p eratures was not prom isi ng, and at high tem p eratures regeneration becam e costly.

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### Electrodialysis (ED) and Electrodialysis Reversal (EDR) Electrodialysis (ED) Most salts dissolved in water are ionic, bei ng positively (cationic) or negatively (anionic) charged. These ions are attracted to elec trodes 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 membra nes are arranged alternately. A spacer sheet that permits feed water to flow along the f ace 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 charge d electrodes. Positively charged ions (Na + etc) migrate to cathode and negatively charged ions (Cl - etc) migrate to anode.

Cathode ( - ) Anode ( + )

Figure 10 – An ED un it in op eration (So u r ce: Electrosynt hesis C o m p any Inc)

During m i gration the charged ions are rej ected by si m ilarly charg e d ion exchange

m e m b ranes. As a resu lt, wa ter within the a l terna t e com p artm ent ge ts con centr ated leaving des a lted wate r within th e nex t com p artm ent of the ED unit. The concentr ate a n d desalted water are continuously removed from the unit. T h e basic electrodialysis unit consists of several hundred cell pairs bound toge ther with electrodes on the outside and is referred to a s a m e m b rane stack.

ALL Consul ting, LLC 18Feed 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-pr essure pump with enough power to overcome the resistance of the water as it passes th rough the narrow passages. The raw feed water must be pre-treated to remove materials th at could harm the me mbranes or clog the narrow channels in the cells from entering th e membrane stack. A re ctifier 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 st abilizing the water and prepari ng it for distribution. This post-treatment might consist of removing gase s such as hydrogen sulfide and adjusting the pH.

Electrodialysis Reversal Process (EDR) An EDR unit operates on the same general prin ciple as a standard electrodialysis plant except that both the product and the brine channels are iden tical in construction. At intervals of several times an hour, the polarity of the electrod es is reversed, and the flows are simultaneously switched so that the brin e 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 th e 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 mi nutes, 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 re versed 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 Re verse 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 H 2 S, oil, acid, BTEX, dissolved solids etc. About 93% of total TDS (8,300 to 10,000 ppm) is accounted for as sodium, chlo ride, calcium and bicarbonates. Oil and grease content was about 65 ppm and BOD va lue 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 vi a 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 oxi dation of dissolved organics.

3. Desalting/Demineralization using an ED unit.

ALL Consulting, LLC 19ED provided economical demineralization in th is case. The feed water had approximately 9,000 ppm TDS. As usual, the cost of the ED unit operation increas es as the required TDS removal increases. Table 5 shows th e overall removal of contaminants using different treatment technologies. The ED re moved 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 (HEED TM ), Frac Water Inc: Frac Water Inc developed mobile ED treatment units for treating CBM produced water and reusing it in fracturing treatment. Seve ral 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 (140 o 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 fou ling 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 trea tment units from Frac Water Inc. ED treatment primarily recovers 80-90% of brackish water. The patents-pending electrodialysis HEED TM 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 20Figure 11 – Mobile ED treatment traile r developed by Frac Water Inc



### Capacitive Deionization Technology (CDT) Capacitive deionization technology (CDT) is a new technology bei ng developed for the purification of ocean and brackish ground wate r. 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 pro cesses. In CDT, a br ackish water stream flows between pairs of high su rface area carbon electrodes th at 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 oppos ite 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 (NO 3 ). Eventually the electrodes become saturated with ions and must be regenerated. The applied potential is removed, and the elec trodes are flushed to release attached ions from the system, pr oducing the more concen trated brine stream.

The current carbon aero gel electrodes provid e approximately 500 m 2 /g surface area. They provide high electrical conductivit y and high ion permeability. Carbon aero gel electrodes are expensive and their ion storag e 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 pr ovide higher surface area. CD T System Inc is developing impregnate of carbon nanotubes on the RF resins.

ALL Consulting, LLC 21Figure 12 shows conceptual di agram of CDT. Unlike ion ex change, exchange of ions does not occur; ions are adsorbed within th e pores of charged electrodes under the effect of capacitance.

Positive electrode attracts negatively charged ions (anions). Chloride (Cl - ) Nitrate (NO 3 - ) Silica (SiO 2 - ) 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 th roughput capacity of a 28 ft. mobile CDT unit, which includes 30 AquaCells with the capability to be field expanded

ALL Consulting, LLC 22to 88 AquaCells. The expected quality of treated water is fixed at 500 ppm TDS for drinking water and 1000 ppm TD S for agriculture water.

Table 7 – Treatment capacity of CDT unit Feed Water TDS, ppm Capacity, Pota ble 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) technol ogy is an innovative water disinfection technology which involves the exposure of wate r, and the natural sa lts, 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 elect rolysis 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 wate r type of application. With this technology the natural water chemistry is used to produce highly eff ective disinfection agents that would destroy viruses and bacteria.

Typically activated water would be dosed be fore and after the CDT AquaCells. Dosage before reduces the overall orga nic 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 wate r technology is that the dosag e 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 dioxi de, 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, an d a DC electrical field. In EDI, ionized species are removed much like conventional el ectrodialysis (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 re moved under the influence of the DC electrical field. In effect, ionized sp ecies are removed in one area of an EDI stack, and weakly-ionized species are removed in a second area.

ALL Consulting, LLC 23Figure 13 shows the removal of ions as wa ter travels through the EDI cell. Strongly ionized species are removed first in the fl ow path and weakly ionized species are removed as the water moves down the flow pa th. 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 un its in various power plants and semiconductor plants in the US. Table 8 shows the average removal of weak ly 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 ab le 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 requ ire 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 c oncentration of salts/solids.

Falling film vertical tube evaporators [16] have the highest heat transfer coefficient which is required to save energy. It also mini mizes 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 por tion 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. Compresse d 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 ev aporator sump is continuously discarded through a blowdown valve to maintain density of the slurry in the evaporator. The concentrated blowdown can be disposed th rough a class I inject ion well or can be converted into solid wast e 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 deve loped a Rapid Spray Evaporation TM (RSE) system of ejecting contaminated water at high velocitie s through a specialized injector-nozzle into waste heat. The unit uses a heating element fo r a heat source across which air is blown into the evaporation chamber. As the heat ed air moves along the evaporation chamber, nebulized wastewater is injected into th e evaporation chamber. The moving vapor and brine droplets pass through a mechanical filter which traps the brin e droplets. The pure vapor phase passes on to a condenser. The brin e droplets are period ically flushed from the filter with the water being treated.

As the water vaporizes within milliseconds of ejection, the so lids in the solution flash or separate out. The water vapor is condensed a nd collected while the precipitated solids form isolated crystalline particles, which ar e collected through a vacuum process and sold as a byproduct. RSE ejects the salt water throu gh a nozzle into a stream of heated air, forming a mist of droplets which vaporize almo st instantly. The minute flakes of solid salt left behind fall to the bottom of the evapor ation 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 c ontaining up to 16% salt. The operating costs for RSE are about one-third of the cost of conventional desalin ation methods alone, producing 1,000 liters of fresh water for between 16 and 27 cent s. AquaSonics claims to attain nearly 100% salt conversion of salt water into fresh wate r. 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 se parate freezing pad which consists of an

ALL Consulting, LLC 26elevated pipe grid with strategically placed sprinklers. These sprinklers can be raised as the ice builds up on the pi pe grid. The unfrozen brine water drains from the ice grid and is separated using condu ctivity-controlled valves.

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

The concentrated brine water is then transp orted to separate storage ponds for either secondary treatment or for disposal. Figur e 14 shows a picture of Spray Freezing unit with sprinklers. The alternate to Spray Freezing process involve s 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 fi rst 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 w ith 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; a nd 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), Ultraf iltration (UF), Nanofiltration (NF) and Reverse Osmosis (RO) utilize high pressure across the membra nes to accomplish filtration of contaminants from the produced water. These technologies are the most common techniques of water purification. The membranes are also cont inuously being upgraded or modified for superior performance. Various applicatio ns 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 certai n 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 CO 2 , H 2 S 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 us es the operating pressure higher than the osmotic pressure of salt present in the wate r 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 lowe r concentration solution to attain natural equilibrium. The notion of these filtration t echnologies is discussed in the literature [19]

. In gas-liquid separation, the pr essure 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 CO 2 to pass through) is applied. Gas penetrates into the membrane at a rate that depends on diffusivity and solubi lity 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 exploi t the clear advantages of using mobile produced water treatment units. Osmonics Inc, one of the leading manufacturers of membranes focusing

ALL Consulting, LLC 28on produced water treatment applications, has been developing high performance compact membrane (such as sp iral wound membrane) modules [20] . These membrane modules are easy to utilize in mobile syst ems. 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 memb ranes is reduced by hi gher 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 an d so more energy is required to achieve desired separation. However, higher temper ature reduces the visc osity of the solution which somewhat offsets the temperature effect [21] . The pH of the solution is also an important factor during the membrane f iltration operations. High pH RO operation effectively removes boron if the membrane can sustain high pH.

Membrane fouling is a common problem in th e various membrane filtration processes. Higher flow rate through the membrane module can produce enough shears near the membrane to avoid accumulation of oil a nd fouling agents. A hydrophilic membrane is less prone to oil fouling as it has a higher affi nity for water and abili ty to reject oil and grease. New Logic Research developed vi brating membrane mechanism to avoid membrane fouling caused by fr ee oils and scaling agents [22] . The sinusoidal vibration of the membrane avoids the migration of collo ids 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 (P RRC) of New Mexico Institute of Mining and Technology has developed inorganic memb ranes for the produced water treatment focusing on the treatment of high salinity pr oduced water (> 50,000 ppm in San Juan and > 100,000 ppm in Permian basin). The inor ganic 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 pre ssure and higher flux operations. Each row is for different membranes.

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

Membrane Ions in feed TDS, ppm Pressure, psi Flux, kg/m 2 .h Rejection, % 1 Na + , K + , Ca 2+

, Mg 2+ , NH 4 +

, Cl 39,000 350 0.112 74.5

2 Na + , Cl - 5,500 300 0.135 89.2 3 Mg 2+ , Cl - 9,400 300 0.081 68.6 4 Ca 2+ , Cl - 11,000 300 0.096 57.6 5 Na + , SO 4 - 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 th e surface at 185°F with approximately 10,000 ppm of salt, a high level of su spended solids and free oil.

The three-step membrane separation combined with an ion exchange step proved to be sufficient to yield water suitable for irri gation (< 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 Ex change 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 Re cy cl e

Perm eate Treated Wat er Re cy cl e 12,000 GPD From oil/water separa tor

Cartridg e filter UF, 185 ° F

N F, 185 ° F To oi l/wat er sep a rator

Disposal / R e inj ect ion

Figure 17 – G E p r o d u ced wa t e r t r eat m e nt sy st em , C a l i f or ni a

The pH of t h e produced water from the oil sepa rator s was adjusted to 5. 8 with sulf uric acid. The suspended solids were allowed to se ttle in a tank with a conical bottom

. CO 2

ALL Consul ting, LLC 30and H 2 S 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 th rough high temperature UF, NF and RO units followed by cooling operation and a low temperature RO un it. The overall system recovery was more than 80% considering the recycling of th e 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 (f in-fan), trickling filte r, ion exchange and reverse osmosis. The warm softening pr ocess removed approximately 95% hardness from the produced water. Silica levels in th e softening effluent were 80 and 20 mg/l at a pH of 8.5 and 9.5, respectively. Silica le vel decreased to 3 mg/l when 400 mg/l of MgCl 2 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 a bove. 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 vari ed 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, MgCl 2 and ionic polymer were added to the produced water in orde r to precipitate cal cium and magnesium hardness. Equation 6 shows the removal of bicarbonate hardness by addition of lime.

OH CaCO OHCa HCOCa 2 3 2 23 22)()( + → + ..(6)

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

Process Specifications Treatment Comments

Warm softening 100 gpm throughput with 10 gpm/ft 2 precipitate rising rate Hardness, Boron, Silica, Ammonia removal sodium hydroxide/ polymer MgCl 2 addition

Cooling Fin-fan heat exchanger cooling effluent from softening unit necessary to prevent damage of the downstream units Trickling filter 400 ft 3 of polypropylene packing 2.5 gpm/ft 2

Hydraulic loading Biological oxidation of organic carbon effluent with < 2 ppm TOC

Ion Exchange 5 ft 3 of Ionac C-249 resin with capacity of 25-30 grains/ft 3 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 Filters Ion Exchange RO Produced Water

Figure 18 – Sc hem a ti c of p r o duce d wat e r t r eatm e nt pr oces s
Also boron, silica and ammonia were rem oved up to som e extent in the Lim e Sof t ening process. The effluent from the softening proc ess was discharged to a fin-fan type heat exchanger to cool the w a ter from more th an 150 °F to jus t ab ove am bient air tem p erature

ALL Consul ting, LLC 32as the units downstream of the softening unit we re susceptible to damage at temperatures above 100°F.

The next step was the tric kling 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 pres ence 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 degrad ed by the biological film. As the biological film thickens through microbial growth, oxyg en 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 pressu re 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-gall on 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 adjustme nt during the process. For example, as the pH of the solution increases more sili ca gets ionized and that increases silica solubility, which may increase membrane l eakage and deteriorates the silica removal. Opposite to that, as the silica solubility increas es the chances of memb rane fouling due to silica precipitation decreases, which improves RO membrane performance. As the pH of the solution increases ammonia solubility d ecreases, which diminishes ammonia removal by RO. 

### High Efficiency Reverse Osmosis (HERO TM 

### ) Ionics Inc developed HERO TM [26] to provide higher water recovery, higher quality permeate, higher operating flux and lower overa ll cost than conventional RO treatment. The most important stage of HERO is pretreat ment of the feed water before RO operation to raise the pH of feed water which enable s higher efficiency. As discussed earlier, increase in pH improves boron remova l 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 332. Carbon dioxide removal : As discussed in earlier sect ions, degasification using air stripping removes carbon dioxide from the wa ter. 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 Aci d C a t i on Exc h ange Carbo n Dio x ide R e m oval RO

Alk a li ( if ne eded ) Alkali Acid ( if n e ed ed ) Perm eate

Co n c en tr a t e

Figure 19 – A schem a t i c of H E R O sy st em devel o ped by I o ni cs I n c The biggest advantage o f the HERO system is t h e reduced capital cost (~15%) at h i gher flux rate (5 0 GPM). Because of red u ced fou lin g and scalin g of the RO m e m b rane, the operating and energy costs for HERO are also le ss than conventional RO. The increase in
water r ecov e ry is obv ious with HERO syst em s due to the high perform a nce of

m e mbrane. The shortcom ings of HERO are th e treatm e nt chem ical requirem e nts and the higher costs at lower flux operations.

Ionics Inc tested a HE RO system to upg ra de the water purif ica tion plan t of S a ndia National L a boratories at Albuquerque, New Me xico. The system produced approxim a tely 94% water recovery. The reported power usage was approxim ately 17 kW h per 1000 gallons of treated water. The reported operating cost was approxim a tely $0.064 per gallon of treated water.



### Oxidation Reactor Newpark Environm ental Services offers an innovative treatm ent system consisting of several com ponents and is base d on aggressive oxidation foll owed by precipitation of the
contam inants present in the produced water [28] . Oxidation of contam inants is the m o st im portant p a rt which is accom p lished in HB Reacto r , a p r oprietary d e sign of Newpark Environm ental Serv ices. HB Reactor is the pa rt of che m ica l/physical treatm e nt stage of this m u lti-stage technology. Chem i cal/phy sical stage is often adequa te to ach ieve m a ny water treatm ent requirem e nts on its own. Dissolved contam inants such as m onovalent salts are extrem ely resis t ant to oxid a tion / pr ecipitation and m a y not be rem oved during chem ical/ph y sical treatm ent stage. Such co ntam inants can b e rem oved in the dem i neralization stage which c onsists of MF, U F and/or RO units. The chem ical/physical
trea tm ent stage bef o re the dem i neraliza tion st ag e rem oves contam inants that can p l u g the

m e mbrane and im proves efficiency of the dem i ne ralization stage.

ALL Consul ting, LLC 34The Newpark system contains three separate st ages that can be used separately or in tandem: the chemical/physical stage, the demi neralization 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 CO 2 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. Wa ter/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 a ssociated with positively char ged ions) in the form of a contaminant (Ca + CO3 - , Na 2 + SO 4 -2 etc.).

Figure 20 – HB Reactor for aggressive oxidation of contaminants – proprietary design (Source: Newpark Environmental Services)

ALL Consulting, LLC 35The charged micro-bubbles attract more oppositely charged contaminants and become thicker which increases their su rface tension conti nually. Due to ever increasing surface tension, the size of th e micro-bubble decreases and the pressures and temperatures inside the bubble signifi cantly increase, which creates points of highly localized temperature. Under the effects of increased pressure and temperature contaminants attached to micro-bubb les are violently reacted with O 2 associated with atmospheric air inside the micro-bubble. The energy associated with this reaction results in ultrasonic wave and a very a ggressive oxidation of contaminants. Those contaminants not oxidized are highly energized and in a very reactive state. The water (along with the oxidized a nd energized ions/contaminants) flows out of the reactor to the next stage.

• Degasser – at this stage all O 2 has been consumed but a significant amount of N 2 remains trapped in the water. Degasser removes the trapped N 2
.

• Coagulation/Flocculation – a coagulant (lime) and flo cculent (anionic polymer) is mixed into the water to precipitate out th e 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 contaminan ts 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 a nd 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 gene rally hauled to the nearest di sposal facility. Large volumes of concentrate, transportation costs, and limited capacity of dis posal sites encourage further treatment of concentrat e. 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 36associated TDS increases significantly. Th e water (extract phase) is re-circulated through the RO and concentrat e (sludge-water) flows throug h evaporators. Water gets evaporated and the dissolved solids remain in sludge state. Hand ling and disposal of reduced volume of waste in sludge form is easier.

Figure 21 shows a schematic of produced wa ter 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 CH 4 recovery CO 2 removal Clasiker SS Removal HB Reactor Oxidation Degaser N 2 removal

Settler

Frictioning Large flocs removal Clarifier Contaminants removal

Finer flocs removal Activated

Carbon

Polishing

stage

MF RO Produced Wate r

Sludge Disposal Evaporator Stage 1:ChemicalPhysical

Stage 2: Demineralization

Stage 3: Waste disposal Crystallizer Sludge

Sludge Sludge

Concentrate Water Recovery Concentrate Permeate Treated Water Ai r

pH Ven t

Sludge

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

ALL Consulting, LLC 37Table 14 shows the performance of Newpark’s system for the treatment of produced water from three facilities. The quality of effl uent or treated water at the end of both the chemical/physical treatment stage and demi neralization stage was supervised. The Pinedale and Gillette plants are company-ow ned 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 (CO 3 ) < 1 - - < 1 < 1 < 1 < 1 - < 1

Bicarbonate (HCO 3 ) 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 CaCO 3 582 - - 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 solub ility 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 precipi tates scale containing high concentrations of radium in the form of barium sulfate or ba rite [Equation 7] under the effects of varying temperature and pressure dur ing the production operations.

4 4 ][ SORaBaSORaBa →++ − + + ..(7)
The handling and treatment of the precipitated sulfate deposits containing decaying radioactive materials is absolute necessity be cause of the dangers of radioactivity. BPF Inc., Texas [30] , developed mobile automated treat ment includes separation of NORM

ALL Consulting, LLC 38solids from other oil field waste (produ ced water) containing less than 30 pCi/g (Picocuries per gram, a measurement of radi oactivity) 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 NO RM containing solution is transported to class II injection site and reinjected into the formation.

Radioactive materials also occur in natural ga s 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 NOR M treatment which is accomplished by in-situ radio-assay capability.

ALL Consulting, LLC 39

## Handling of Water Treatment Waste/Concentrate Produced water treatment technologies c onvert poor quality pr oduced water into good quality water by removing contaminants and impurities. As discussed earlier, many of such treatment technol ogies decontaminate inlet pr oduced water producing a waste stream with higher concentr ation of contaminants and a treated water stream. For example, membrane systems separate influe nt 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. Considerin g large scale of produced water treatment, the amount of concentrated waste volume need s to be considered when planning water treatment facilities.

The selection of concentrate disposal practi ce depends on several factors such as regional disposal availability (geology, geographical. climate etc), local avai lability (existence of suitable disposal site, distance, compatibil ity etc), volume of concentrate stream, applicable environmental regul ations (NPDES, underground in jection control regulations, and underground water resource regulations et c. are imposed by local, state or federal agencies), environmental impacts, public reception, cost, etc. Along with cost contributing factors such as tr ansportation, treatment, develo pment of disposal site, etc; environmental regulations also have major im pact 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 c ontaminants in it are some of the limiting factors for this practice.


### Disposal to sewer: NPDES permit is not required for the dispos al 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 Cl ass I injection well beneath the lowermost underground source of drinking water require s 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. Th is technology is limite d to regions where

ALL Consulting, LLC 40solar irradiation is high which results in higher eva poration 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 ev aporation if the poten tial of waste runoff to a receiving water body exists. 

### Zero liquid discharge: The objective of zero liquid discharge is to e liminate any liquid waste at the end of the water treatment. Evaporators or concentrators can be utilized to conc entrate waste stream. Conversion of concentrated sludge into soli ds/salts form can be accomplished by using crystallizer. Disposal of solid waste from cr ystallizer 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 fiel d applicability. Within each objective (for example “De-oiling”), technologies can be compared in terms of their advantages, disadvantages, resulting waste st ream, 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. Compar isons of inherent durability can be made within each objectiv e but these are only generalizations. No attempt was made to ascribe economic factors to these technologies si nce costs will vary from location to location a nd may be dependent upon comme rcial configurations and innovations.

Waste products are specific to each technology; for example desalinization can result in a residue consisting of 20% of th e 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 st andard industrial wast e 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 subj ect to increased regulatory compliance costs.

Applications might include specific oil and gas operations as well as general producing situations. Applications include the treatmen t 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 de scription of certain applications.

ALL Consulting, LLC 42Treatment 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
p eroxide/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 CO 2 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 43Treatment 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 lesspower 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, filtratewaste from posttreatment stage
Capacitive deionization ionized salts are adsorbed b y 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 44Treatment 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 45Treatment 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 stri p ping of dissolved gas from water concurrent or countercurrent operations, cheaper p ost treatment, lower efficiency



### Ranking The effectiveness and performance of the va rious treatment technol ogies can also be analyzed according to a new five-step ranki ng 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 a nd as innovations are installed and made newly available. The ranking of each step depends on the ranki ngs of other steps. Reasonable engineering judgment and experi ence 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 th e product of the authors, and are subject to change.

Step 1 – Ability to remove t echnology specific contaminants: The simplest method to express the perf ormance of a treatment technology is the removal of contaminants in percentage. Ra nking 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 46Step 2 – Consumption of resources to achi eve desire removal using given technologies: The consumption of resources in terms of effort, cost, energy, natural resources, etc. must be considered in ranking. As st ated earlier regarding the interdependency of ranking criteria, in the case of RO operatio n, higher pressure across the membrane (energy) is required to achieve higher rem oval 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]. Fo r the same membrane and contaminants level >95% [rank 5] removal requires hi gh energy [rank 2].

Step 3 – Requirement of pre- or post-trea tment technologies with given technologies: Most of the treatment technologies requi re pre- or post-treatments to improve efficiency, to achieve better quality, to ha ndle byproducts, etc. Th e extent of such requirements significantly contributes to the overall performance but also adds to cost, facilities, and technol ogical complexity. Ranking a ssigned 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. + tech nologies in previous sections 3

Moderate : regeneration, fouling prevention, trickling filter, construc ted 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 activ ation of pumps and valves to move fluid while other technologies feature simpler flow paths that are gravity-driven. Simpler

ALL Consulting, LLC 47technologies are easier to main tain 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 technologi es to be performed as mobile units benefits the produced water treatment and a dds 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 individua l technologies can be performed by mobile units. However, they ma y require pre- or post-treatments which can only be performed by fixed units. Such operati ons 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 ga s 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 al so 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 48Medium : 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, mo novalent 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 step s, the final formula as described below calculates overall rank. The possi ble highest rank is 7 and the least possible rank is 1. On the scale of 7, the treatment technologies w ith 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 wa ter [step 6, rank 5] with low pressure RO [step 2, rank 4]. Th e 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 poi nts. Even the difference of 0.05 can be significant. The following table compares performance of HERO TM (high efficiency RO) and HEED TM (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 bett er performance with HERO TM system and highlight that system’s higher efficiency in spite of requiring more resources. Th is ranking was made on the basis of individual, hi storical 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 49of the ranking mechanism. This ranking scheme can be applied to a range of technological options for treating produced wa ters. 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 c hosen end use for the water.

ALL Consulting, LLC 50

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ALL Consulting, LLC 52ALL Consulting, LLC 53 26. Hayter S., Tanner S., Urbatsch E., a nd Zuboy J.: “Saving Energy, Water, and Money with Efficient Water Treatment Technologies,” DOE/EE -0294 (June 2004), A New Technology Demonstration Public ation, Federal Energy Management Program.

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