MEMORANDUM 

TO: Public Record for the Effluent Limitations Guidelines and Standards for Drinking 

 Water Treatment Facilities 

 EPA Docket Number: EPA-HQ-OW-2008-0517 (www.regulations.gov), DCN 10003 

FROM: Paul Hanson, P.E. 

PG Environmental LLC (PG) 

DATE: 30 August 2010 

SUBJECT: Ion Exchange for Produced Water Treatment 

EPA requested PG assemble literature data on ion exchange. 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 (ALL 2006a). Ion exchange is considered to be an 

efficient process, with low energy demand, possible continuous regeneration of resin, and systems can be 

mobile (ALL 2006a). Ion exchange is the primary produced water treatment method in the Powder River 

Basin (PRB) (ALL 2006b). This memorandum discusses the process, performance, and residuals. 

Description of the Treatment Process 

Ion exchange (IX) is a physical-chemical process by which ionic contaminants are removed from the 

water (US EPA 2000). The ion exchange process effectively removes arsenic, heavy metals, nitrates, 

radium, barium, strontium, salts, uranium, and other elements from produced water (ALL 2006a). Ion 

exchange is a reversible chemical reaction wherein positively or negatively charged ions present in the 

water are replaced by similarly charged ions present within the resin (ALL 2006a). The resins immersed

in the water are either naturally occurring inorganic zeolites or synthetically produced organic resins 

(ALL 2006a). To accomplish this exchange of ions, feed water is continuously passed through a bed of 

ion exchange resin beads in a down-flow or up-flow mode until the resin is exhausted (i.e., when all sites 

on the resin beads have been filled by contaminant ions) (US EPA 2000). When the replacement ions on 

the resin are exhausted, the resin is recharged/regenerated with more replacement ions (ALL 2006a). The 

number of bed volumes that can be treated before exhaustion varies with resin type and influent water 

quality. Typically 300 to 60,000 (up to 300,000) bed volumes can be treated before regeneration is 

required, depending on the adsorptive capacity of the resin and the feed water quality. (US EPA 2000). 

Residuals include backwash/rinses and regeneration waste. Product water and regeneration wastes may 

require pH stabilization. 

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

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

classified as: 

Strong Acid Cation (SAC) Resins (ALL 2006a): 

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

 or Na+ ions 

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

removal with SAC. 

(1) 2(R – SO3H) + NiCl2 → (R – SO4)Ni + 2HCl 
Equation 2 shows an example of Ca+ softening with SAC. 

 (2) 2(R – SO3H) + Ca+ → (R – SO3)

2Ca + 2H+

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

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

exhaustion, the resin is regenerated to the hydrogen form by contact with a strong acid 

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

Weak Acid Cation (WAC) Resins (ALL 2006a): 

Weak acid resin has carboxylic acid (COOH) group as opposed to the sulfonic acid group (SO3H) 

used in strong acid resins. These resins behave similarly to organic acids that are weakly 

dissociated. WAC has high affinity for divalent salts. Equation 3 shows an example of Ca+

softening with WAC. Alkalinity present in bicarbonate form also can be removed by WAC. 

(3) 2(R – COOH) + Ca+ → (R – COO) 2Ca + 2H+

 

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

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

carbon dioxide or decarbonation (Moftah 2002) is necessary during the water treatment 

process. 

(4) HCO3

-

 + H

+ → H2CO3 → CO2 + H2O 

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

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

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

stoichiometric amounts of acid. The degree of dissociation of a WAC is strongly influenced by 

the solution pH. Consequently, resin capacity depends in part on solution pH. 

Strong Base Anion Resins (ALL 2006a): 

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

are used in the hydroxide (OH-

) form for water deionization. They will react with anions in 

solution and can convert an acid solution to nearly pure water. Equation 5 shows the reaction 

involved in an anion exchange step. 

(5) (R – NH3OH) + HCl → (R – NH3Cl) + HOH 

Regeneration with concentrated sodium hydroxide converts the exhausted resin to the hydroxide form. 

Weak Base Anion Resins (ALL 2006a): 

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

resins sorbs anions associated with weak acid. 

EPA observed numerous ion exchange installations in the Powder River Basin as part of its site visit 

program (see Attachment A). EMIT Water Discharge Technology, LLC (EMIT) Higgins LoopTM 

continuous counter-current IX systems are the most commonly used IX systems in the PRB (Johnston 

2010b). The EMIT process utilizes a strong acid cation exchange resin, which has a sulfonic acid group 

that exchanges sodium, barium, calcium, and magnesium ions with hydrogen ions (ALL 2006a). Because 

divalent ions (Ca, Mg, etc.) are favored over monovalent (Na, etc.) ions by the resin for replacement,
calcium and magnesium often need to be added back to the treated water to reduce the Sodium 

Absorption Ratio (SAR). EPA observed a pilot scale Drake Water Technologies, Inc. (Drake) process 

that selectively targets the removal of the sodium ion from CBM produced water (U.S. EPA, 2010). 

Operational Limitations 

TDS Limitations 

The average TDS application range is between 500 mg/L and 7,000 mg/L (CSM 2009). EMIT estimated a 

cation load of 1,600 to1,700 mg/L is the approximate breakpoint when it becomes uneconomical to treat 

CBM produced waters. EMIT has successfully treated CBM produced waters at cation loads up to 1,500 

mg/L (Johnston 2010b). 

Fouling and Scaling 

Ion exchange requires pretreatment against fouling agents, including suspended solids, oxidized metals, 

and scaling minerals (e.g., CaSO4) (CSM 2009). Oil and grease and iron bacteria are two constituents that 

must be removed prior to ion exchange (ALL 2006b). Occasional chemical disinfection of the resins may 

be required to mitigate biofouling and will typically consist of H2O2 or NaOCl cleaning solutions (CSM 

2009). Additionally, many IX resins are sensitive to free chlorine oxidation. IX processes must also be 

carefully managed to reduce osmotic shock and mechanical abrasion of IX resin, which will lead to 

physical loss of the resin (Dow Chemical 2005). 

Temperature 

Acid cation resins should not be exposed to feed temperatures in excess of 120°C, while base anion resins 

are limited to 100°C or lower (CSM 2009). 

Variable Feed Water Volumes 

In order to handle variable quantities of water, some operators are exploring using two or more smaller 

capacity units and bringing on line the number of units to handle the capacity as needed instead having 

one large capacity unit (ALL 2006b) EMIT reported units treating as little as 6,000 bbls/day, and that 

they recently completed a 125,000 bbl/day treatment system. (Johnston 2010b) 

Performance Data and Costs (What discharge levels can these treatment systems meet? Do costs 

vary with levels of discharge? Are final effluent concentrations independent from influent 

concentrations?) 

Ion exchange resins are chosen to preferentially adsorb the particular contaminant of concern (US EPA 

2000). Ion exchange can achieve a wide range of results depending on the concentrations in the influent 

stream and how the system is operated and maintained. For example, different types of ion exchange 

resins are available that will yield different performance. The frequency of backwashing, replacement of 

resins, and the nature of pretreatment steps all contribute to how well the system will perform and how 

costly the treatment process will be. (Argonne National Laboratory 2006) Treatment process permeate 

quality is dependent on feed water salinity and operating conditions with greater than 93 percent rejection 

of target ions achievable (CSM 2009). 

Potential Data Sources 

CBM Detailed Questionnaire 

EPA received questionnaire responses from 11 ion exchange treatment processes in the PRB basin (WY 

and MT) and the Green River basin. 
Office of Ground Water and Drinking Water (OGWDW) 

Note for Brian: OGWDW may have some useful data, but drinking water IX is typically focused on Ca 

and Mg softening or anion removal. 

Vendors 

See Attachment A for a list of vendor information in or to be posted to the CBM record. 

Drake provided confidential sampling data from a 7-day continuous demonstration of the Drake 

ion exchange process. Drake design goals are presented in Table 1: 

Table 1. Drake Process Effluent Water Quality Design Goals 

Parameter Value 

SAR 3 

Sodium <100 mg/L 

Electrical conductivity (EC) 1000 μS/cm 

pH 6.5 

Source: US EPA 2007a 

EMIT stated that for the PRB standards that they have been requested to evaluate, they have been 

able to treat water to those standards. EMIT has a wealth of performance data to use in predictive 

modeling because they regularly sample incoming and outgoing water from their systems (as well 

as some intermediate water sampling). EMIT noted that their cost data and monitoring data is 

sensitive customer data. (Johnston 2010b) A sample of EMIT performance data is provided in 

Table 2: 

Table 2: EMIT Performance of Higgins Loop Treatment for a Field Trial at a 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 

Source: ALL 2006a 

Colorado Department of Health and Environment (CDPHE) 

Gary Beers noted that the State of Colorado Water Quality Control Division (WQCD) has issued 3 to 6 

permits where advanced treatment is applied to produced waters before discharge to surface waters. 

Discussions were held with developers and manufacturers of these technologies with a focus on 
performance and general costs. The information on the various technologies and provided cost 

information is to be sent to EPA. (Johnston 2010a) It is unclear at this time if any of this data is for ion 

exchange. 

Montana Department of Environmental Quality’s (MDEQ) 

MDEQ’s Board of Environmental Review (BER) proposed technology based limits (MDEQ’s Proposed 

Rule VIII) in 2005 to restrict discharges or CBNG produced water. 

NEW RULE VIII TRATMENT-BASED EFFLUENT LIMITATIONS 

 (1) If the department grants a waiver from the zero discharge requirement for all or a portion of 

the wastewater pursuant to [New Rules II and III], the amount of wastewater that obtains the 

waiver shall achieve the following minimum technology based effluent limitations at the end of 

the pipe prior to discharge: 

(a) calcium average concentration between 0.1 mg/L and 0.2 mg/L; 

(b) magnesium average concentration between 0.1 mg/L and 0.6 mg/L; 

(c) sodium average concentration of 10 mg/L; 

(d) bicarbonate average concentration of 30 mg/L and instantaneous maximum concentration of 

115 mg/L; 

(e) sodium adsorption ratio instantaneous maximum of 0.5; 

(f) electrical conductivity average concentration of 233 μmhos/cm; 

(g) total dissolved solids average concentration of 170 mg/L; 

(h) ammonia average concentration of 0.1 mg/L and instantaneous maximum concentration of 

0.3 mg/L; and 

(i) arsenic concentration of <0.0001 mg/L.” 

Comments on Proposed Rule VIII questioned the achievability and affordability of the Montana limits, 

and noted inconsistent treatment levels for several parameters. Comments also noted that the proposed

limits were below drinking water standards, creating water that may be detrimental for beneficial use 

(e.g., leaching minerals and metals from soil), as well as noting additional environmental impacts from 

increased waste volumes (e.g., waste hauling traffic). (ALL 2006b, Sattler 2006, Argonne National 

Laboratory 2006). One report provided costs, but noted that the costs for the proposed Montana standard 

may be as much as an order of magnitude greater than current costs for treatment and discharge (ALL 

2006b). 

Bureau of Reclamation Desalting Costs 

The Water Treatment Estimation Routine (WaTER) User Manual (Wilbert 1999) provides ion exchange 

costs. 

U.S. Department of Energy Desalting Costs 

The U.S. Department of Energy provided cost estimates for ion exchange in the PRB based on TDS limits 

of 500 and 1000 mg/L (Bank 2006). 

University of Wyoming The University of Wyoming developed a decision model for treating CBM water 

(Sajtar 2008). 

Colorado School of Mines 

The Colorado School of Mines is developing a Produced Water Treatment and Beneficial Use Screening 

Tool. This tool will provide water quality (based on geographic location), suggest suitable treatment 

trains, and provide a cost-benefit analysis of different beneficial reuse options for the water. 
Typical Disposal Practices of Waste Streams and Volumes of Waste as Compared to Volumes of 

Treated Influent 

Brines are produced from rinsing, regenerating, and backwashing the ion exchange unit. The spent media

residuals are mainly solid waste media and the contaminants absorbed to it. 

The waste characteristics are highly dependent on the nature of the process water and the treatment 

processes incorporated. The predominant ion in the spent regenerate streams is often the co-ion in the 

regenerant (e.g., chloride, sulfate, carbonate, or sodium) (AWWA, ASCE 1996). The other ions present 

are those removed by the resin and reclaimed by the regenerant. With chlorides present, brine is corrosive 

to materials it contacts. The pH of the spent regenerant could be low or high depending on the type of

resin used. For example, a cationic exchange resin may be regenerated using concentrated sulfuric or 

hydrochloric acid, while an anionic exchange resin may be regenerated using a strong base(U.S. EPA 

2007b). In addition to the spent regenerant waste, IX generates backwash water used before and after 

regeneration. 

Table 3 summarizes the typical residuals generated from drinking water ion exchange and potential 

pollutants in each waste stream. (AWWA, ASCE 1996; AWWA & AWWARF 1987). 

Table 3. Drinking Water Treatment Processes and Waste Streams 

Typical Residual Waste 

Streams 

Typical Waste Stream 

Constituents 

Brine stream 

(regenerate waste) 

TDS 

Metals 

Hardness 

Calcium 

Magnesium 

Sodium 

Sulfate 

Chloride 

Nitrates 

Radionuclides 

Rinse water and/or backwash Dilutes regenerate waste 

Of these streams, the regeneration stream contains the highest levels of TDS, ranging from 10 to 300 

times the levels found in drinking water feed water (US EPA 1993). This high TDS content is due to the

ions removed from the exchange resin during regeneration and excess regeneration ions (US EPA 1993). 

Note that drinking water ion exchange is typically used for calcium and magnesium softening and often 

regenerated using sodium chloride while produced water ion exchange is typically used for sodium 

removal (typically also removing calcium and magnesium) and regenerated using acids. The regeneration 

stream is often mixed with the rinse and backwash streams, diluting the regenerant by as much as an order 

of magnitude (US EPA 1993). 

Regeneration volumes are dependent on regeneration needs, but is typically requires less than 2 percent of 

the product water (2 to 20 bed volumes of rinse water) to restore the adsorptive capacity of the IX resin 

(CSM 2009). EMIT reports concentrated brine volumes average approximately 1.0 percent or less of the 

total loop feed volume in the PRB, depending on the cation loading that is removed from the treated water 

(All 2006b, Johnston 2010b). Drake reported the volume of brine is approximately 1 to 3 percent of the 

influent flow to the treatment units (US EPA 2007a). Drinking water ion exchange concentrated brine is 

reported to vary between 1.5 and 10 percent and to average 15,000 to 35,000 mg/L (US EPA 1993). Note 
that the PRB contains relatively low TDS concentrations and the concentrated brine volumes increase 

with influent TDS concentrations. 

Disposal 

Depending on the ionic species removed, disposal of this material can cause problems, especially if 

discharged to a waterway. High-TDS residuals are often disposed via underground injection, or used as a 

deep fracking fluid; however, the availability of disposal options is highly dependent on geographic 

location and regulatory requirements. Technologies to further concentrate IX residuals include 

evaporation, crystallization, and thermal distillation. POTW’s are not designed to remove TDS and 

Region 3 recently limited POTW’s to accept no more than 1 percent of their daily flow from fracking 

water. 

References 

AWWA, ASCE 1996. American Society of Civil Engineers, American Water Work Association, U.S. 

Environmental Protection Agency. Management of Water Treatment Plant Residuals: Technical Transfer 

Handbook. April 1996. EPA-HQ-OW-2008-0465-0728. 

ALL 2006a. ALL Consulting. A Guide to Practical Management of Produced Water from Onshore Oil 

and Gas Operations in the United States. October 2006. Prepared for US DOE, National Petroleum 

Technology Office. EPA-HQ-OW-2008-0517 (DCN 10000).

ALL 2006b. ALL Consulting. Feasibility Study of Expanded Coal Bed Natural Gas Produced Water 

Management Alternatives in the Wyoming Portion of the Powder River Basin, Phase One. Prepared For 

U.S. Department of Energy National Energy Technology Laboratory Wyoming State Planning Office, 

January 2006. EPA-HQ-OW-2004-0032-2524. 

Argonne National Laboratory 2006. Observations on a Montana Water Quality Proposal. Prepared by 

Environmental Science Division, Argonne National Laboratory, January 2006. ANL/EVS/R-06/2. EPAHQ-OW-2008-0517 (DCN 10004). 

AWWA & AWWARF 1987. American Water Works Association Research Foundation. 1987. Water 

Treatment Plant Waste Management. EPA-HQ-OW-2008-0517 (DCN 10018). 

Bank 2006. The Economics of Powder River Basin Coalbed Methane Development. Prepared for: U.S. 

Department of Energy. Prepared by: Gregory C. Bank, Vello A. Kuuskraa. Advanced Resources 

International, Inc. January 2006. EPA-HQ-OW-2004-0032-2451. 

CSM 2009. An Integrated Framework for Treatment and Management of Produced Water: TECHNICAL 

ASSESSMENT OF PRODUCED WATER TREATMENT TECHNOLOGIES 1st Edition. RPSEA Project 

07122-12. November 2009. EPA-HQ-OW-2008-0517 (DCN 10007).

Dow Chemical 2005. Dow Chemical Company, DOWEXTM Ion Exchange Resins Practical Guidelines. 

Form 177-01537-1006, 2005, 

http://www.dow.com/PublishedLiterature/dh_0064/0901b80380064a0d.pdf?filepath=liquidseps/pdfs/nore

g/177-01537.pdf&fromPage=GetDoc. EPA-HQ-OW-2008-0517 (DCN 10019). 

Johnston 2010a. Notes from 29 January 2010 Teleconference with Gary Beers, Colorado Department of 

Public Health and Environment, on the Colorado General NPDES Permit for Produced Water Treatment 

Facilities (COG840000). July 27, 2010. EPA-HQ-OW-2008-0517 (DCN 10014). 
Johnston 2010b. Summary of EMIT Water Discharge Technology (an Exterran Company) held on 18 

February 2010. July 27, 2010. EPA-HQ-OW-2008-0517 (DCN 10020). 

Moftah, K. 2002. High pH RO for Wastewater Treatment, Pollution Engineering. October 2002. EPAHQ-OW-2008-0517 (DCN 10021). 

Sajtar 2008, Sajtar, Eric T., M.S.; David M. Bagley Ph.D. P.E. Toolbox to Evaluate Treatment 

Technologies for PRB CBM Water. Department of Civil and Architectural Engineering, University of 

Wyoming. February 2008. EPA-HQ-OW-2008-0517 (DCN 10017). 

Sattler 2006. Allan R. Sattler, Malynda A. Aragon, M. Michael Hightower. Technical Review of Proposed 

Changes in Montana Water Quality Standards for Coal Bed Natural Gas Produced Water. Printed 

January 2006, Prepared by Sandia National Laboratories Albuquerque, New Mexico 87185 and 

Livermore, California 94550. SAND2006-0312. EPA-HQ-OW-2008-0517 (DCN 10011). 

U.S. EPA 1993. Large Water System Byproducts Treatment and Disposal Cost Document. EPA 811-D93-002. EPA-HQ-OW-2008-0517 (DCN 10013). 

U.S. EPA 2000. Technologies and Cost for Removal of Arsenic from Drinking Water. EPA 815-R-00-

028. EPA-HQ-OW-2008-0465-0728. 

U.S. EPA 2007a. Final Site Visit Report: Drake Water Technologies, Inc. Gillette, WY (Powder River 

Basin), November 30, 2007. EPA-HQ-OW-2006-0771-0975. 

U.S. EPA 2007b. Identification and Characterization of Typical Drinking Water Treatment Residuals. 

September 2007. EPA-HQ-OW-2008-0465-0555. 

U.S. EPA, 2010. Final Site Visit Report: Drake Water Technologies, Inc. June 16, 2009, Powder River 

Basin, WY. EPA-HQ-OW-2008-0517 (DCN 10032). 

Wilbert 1999. Water Treatment Estimation Routine (WaTER) User Manual. Bureau of Reclamation. 

Water Desalination Research and Development Report No. 43. August 1999. EPA-HQ-OW-2008-0517 

(DCN 10016). 
Attachment A. Ion Exchange Vendors 

Technology Name Vendor 

Technology in Use or Pilot? Operators, if in use 

Site visit completed? 

Reference Materials / OtInformation 

Higgins Loop Continuous Ion Exchange 

EMIT, Severn Trent Services 

In use Pinnacle Gas 

Resources, Black Diamond Energy, Lance Oil and Gas, Fidelity Exploration & Production Co. 

Yes EPA-HQ-OW-2006-0771

EPA-HQ-OW-2004-0032

Remco Metal Recovery Ion Exchange Process 

Remco In use Not available No EPA-HQ-OW-2006-0771

Drake Process Drake The Drake Process has 

operated under several Wyoming DEQ “Permits to Construct” and has received approval for pit treatment by the Wyoming Oil & Gas Conservation Commission. 

Bill Barrett Corporation at their Willow Creek Plan of Development 

Yes EPA-HQ-OW-2006-0771

EPA-HQ-OW-2006-0771EPA-HQ-OW-2006-0771EPA-HQ-OW-2008-0517 10032) 

Ion Exchange Triwatech, 

LLC Treatment System 

Triwatech, LLC Pilot Plant Yes EPA-HQ-OW-2006-0771

RecoPur water treatment system /RecoFlo Short Bed Ion Exchange Technology 

PureTech LLC, Eco-Tec equipment 

Near Completion Marathon Oil Company Yes EPA-HQ-OW-2006-0771

EPA-HQ-OW-2006-0771 EPA-HQ-OW-2006-0771EPA-HQ-OW-2008-0517 10034) 

Fixed-bed dynamic flow ion exchange, with filtration 

SET Corp (formerly RG Global Lifestyles, Inc.) 

In use Yates Petroleum Corp 

(Gilette, WY) 

 Yes EPA-HQ-OW-2006-0771

EPA-HQ-OW-2008-0517 10036) 
Attachment A. Ion Exchange Vendors 

Technology Name Vendor 

Technology in Use or Pilot? Operators, if in use 

Site visit completed? 

Reference Materials / OtInformation 

Advanced “Amberpack” Ion Exchange Treatment Systems 

Watergy Produced Water Solutions, Inc. (in association with Rohm and Haas) 

Not available Not available No http://www.energyexposit

ibitor_list.htm http://www.watergypws.co_technology.html 

Groundwater ion exchange system for arsenic, nitrate, perchlorate, uranium, and chromium VI 

Basin Water Not available Not available No http://www.energyexposit

ibitor_list.htm http://www.basinwater.com

Ion exchange treatment system 

Rohm and Haas 

Not operational at time of site visit 

Anardarko Yes EPA-HQ-OW-2006-0771

Ion exchange (or reverse osmosis), as a component of complete pre-, polishing, and posttreatment 

Triwatech, LLC 

Field pilot Field pilot for BP 

America, Inc.’s CBM operations in Wallace Gulch, Colorado; plus tests for several other operators 

Yes EPA-HQ-OW-2006-0771

Testing has been completedifferent CBM produced wstreams from several opercategorize water quality anmarkets for treatment; howtest results and operator naconfidential and were not EPA.