Coalbed Methane Produced Water In The Western Us

deep-well reinjection, the primary CBM produced water management method employed in these basins. These variations in treatment and disposal options occur despite the fact that currently available water treatment technologies allow almost any water quality requirement or goal to be achieved, regardless of the initial quality or quantity of the source water, although at varying costs.1 The Clean Water Act expresses the necessary level of treatment for discharges to be that achievable with the best available technology at an economically achievable level.

This chapter includes information specific to the treatment techniques predominantly used today for CBM produced water in the western CBM basins, as well as some of the techniques for which significant field-scale tests have been conducted but that are not necessarily currently used on a commercial scale. Costs of these primary treatment technologies are also discussed.

Comprehensive, independent, objective evaluations of water treatment techniques for CBM produced water, their effectiveness, and costs have not been widely available, nor are they easy to conduct because of issues of vendor confidentiality and the many variables to consider in treating produced water in different locations. A broad, independent technical assessment of treatment technologies potentially applicable to CBM produced water, including those used for pre- and posttreatment, desalination, and waste disposal, is currently being conducted as part of a collaborative research project led by researchers at the Colorado School of Mines. The project has released the first edition of its technology assessment in which 54 water treatment technologies and disposal methods were addressed (RPSEA, 2009). The document has served as a source of independent information for the primary CBM produced water treatment techniques discussed in this chapter. The committee also collected information from other published sources as well as from water treatment vendors in the western states.

PRIMARY TREATMENT TECHNOLOGIES FOR CBM PRODUCED WATER

A single water treatment technology is generally optimized to address specific constituents in the water but is not usually effective in treating every potential constituent. Thus, depending on the initial quality of the produced water, its eventual use (or disposal), and desired constituent concentrations, one technique alone may serve the primary treatment purpose, or several treatment techniques may be used in sequence to achieve a desired water quality. Sodium adsorption ratio (SAR, a numeric expression of the concentration of sodium, relative to the concentration of calcium and magnesium in produced water; see also Chapter 2) and salinity (measured as electrical conductivity [EC]) are the constituents of

J. Veil, Argonne National Laboratory, personal communication, May 20, 2009; also D. Stewart, Stewart Environmental Consultants, Inc., presentation to the committee, March 30, 2009.

CBM produced water that usually receive the most focus, although treatment for additional constituents, including fluoride, barium, ammonia, bicarbonate, and some trace elements, may be necessary to meet NPDES, UIC, state, and/or tribal regulatory requirements for surface discharge or subsurface reinjection. Some amount of pretreatment may be required as a compliment to treatment for SAR and EC or for disposal by subsurface drip or deep-well reinjection; pretreatment techniques may include degassing, settling, filtration, coagulation, flotation, and/ or flocculation. These techniques are not discussed further.

Table 6.1 presents the more commonly occurring constituents in CBM produced water and the treatment technologies that are able to effectively remove or substantially reduce the concentration of these constituents: (1) ion exchange; (2) reverse osmosis; and (3) Freeze/Thaw Evaporation (FTE). The table also includes adsorption by cation exchange using zeolites and phytoremediation techniques although these techniques are not in common use for treating CBM produced water at this time. Although organics and biological agents are not known to be present in CBM produced water to any significant degree, they are included in the table for purposes of comparison between technologies. Table 6.2 provides a summary of the principles of operation, advantages, disadvantages, limitations, and relative costs of these treatment systems for CBM produced water. Each of the treatment techniques is then reviewed in detail.

Ion Exchange

Ion exchange treatments have been developed specifically in response to the need to reduce the SAR in the sodium concentration of produced water. Ion exchange systems function by capturing and removing a specific ion type within the CBM produced water. The specific purpose of ion exchange is to remove sodium by replacement with a different cation. By this fact alone, SAR will be reduced. Ion exchange resins capture specific dissolved ions and release other (like-charged) ions. Thus, the concentration of a specific ion of concern (e.g., sodium in agricultural areas) can be substantially reduced. The adsorption characteristics and saturation configuration of an ion exchange resin are specific to the ion targeted and a function of the resin composition. In as much as the fixed- and fluid-bed resin exchange technologies that are being used employ primarily sodium cation-specific resins, these treatment systems do not remove substantial proportions of anions or other cations in the produced water stream.

Exterran Water Management Services has developed ion exchange water treatment technologies that use a modification of a Higgins Loop CCIX technology—a patented process exclusively licensed from Severn Trent Services—referred to as continuous coun-tercurrent ion exchange systems for removing sodium and other cations from produced water. Higgins Loop is the most widely used ion exchange technology for CBM produced water treatment (RPSEA, 2009). Approximately 18 percent of all permitted discharge

TABLE 6.1 Estimated Treatment Technology Effectiveness for Constituent Types in CBM Produced Water

Produced Water Constituents—Effectiveness of Removal by Indicated Treatment Expressed as percentages

TABLE 6.1 Estimated Treatment Technology Effectiveness for Constituent Types in CBM Produced Water

Produced Water Constituents—Effectiveness of Removal by Indicated Treatment Expressed as percentages

Treatment Method

TDS

Specific Conductance

SAR— sodium

Bicarbonate

Barium

Fluoride

Ammonia

Trace elements

Organics

Biologicc Agents

Ion exchange

Effective

Effective

Very effective

Very effective

Very effective

Very effective

Very effective

Variable

NA

NA

Reverse osmosis (RO)

Very effective

Very effective

Very effective

Very effective

Very effective

Very effective

Very effective

Very effective

Very effective

Very effective

Freeze/Thaw Evaporation (FTE)

Very effective

Very effective

Very effective

Very effective

Very effective

Very effective

Very effective

Very effective

Very effective

NA

Zeolites

Effective

Effective

Effective

Ancillary

Ancillary

Ancillary

Very effective

Very effective

Very effective

NA

Phytoremediation

NA

NA

NA

NA

NA

NA

Very effective

Very effective

NA

NA

NOTE: "Very effective" indicates data from one or more studies showing >70 percent removal of the given constituent; "Effective" indicates data from one or more studies showing some and up to 70 percent removal of the given constituent; "NA" indicates not applicable because the method is not optimized for that constituent; "Variable" indicates situation-specific approaches and lack of data to make a determination; "Ancillary" indicates that, although this is not the primary target for the treatment method, the method has proven effective at significantly reducing the constituent concentration. More definitive or precise evaluations of the effectiveness of these methods for applications to CBM produced water were not possible because of the lack of independently acquired and verified data, different pretreatment applications, and different starting produced water qualities in different studies. "Organics" is a nonspecific term and the types of organic constituents treated by a given method may not be the same as those treated with another method.

SOURCES: ALL Consulting (2003, 2005), IOGCC and ALL Consulting (2006), and RPSEA (2009). Other sources used to create this table are cited in the main text corresponding to each treatment method in this chapter.

TABLE 6.2 Advantages and Disadvantages of Common CBM Produced Water Treatment Methods

Treatment Method

Principle

Advantages

Disadvantages

Limitations

Relative Cost

Ion exchange

Extensive use in Powder River Basin; limited trial use in other basins

Selective removal and replacement of sodium using cation exchange resin; ancillary treatment is bicarbonate— TDS reduction; can be combined with secondary treatments for fluoride, barium, ammonia, SAR

reduction

Very efficient specifically for sodium (SAR) reduction; extensive history; low energy requirement; capable of processing large volumes of water; proven technology; all-weather operational; long operating life; operation time of 99% in service; waste stream can be eliminated with marketable dried product or reduced to 5 percent of input volume; certain systems are portable and mobile

Requires large volumes of water to be cost effective; elimination of concentrated brine waste stream may be required; turnkey operation involving hazardous material; requires routine, regular maintenance; resin needs periodic replacement; constituent removal is specific to resin; treatment process specifically targets sodium; can be combined in series for removal or reduction of other constituents

Significant infrastructure; involves hazardous material handling

High initial capital investment cost; relatively low per-unit treatment cost once in operation continued

TABLE 6.2 Continued Treatment

Method

Use

Principle

Advantages

Reverse

Specialized

Pressurized

Highly effective,

osmosis

use in San

filtration

can remove most

Juan, Raton,

through

contaminants; can

Uinta, and

fine-pore

minimize waste

Piceance

membrane

stream for disposal;

basins; trial

proven technique and

use in Powder

technology

River Basin

Freeze-

Application

Distillation by

No energy input

Thaw

specific

freezing and

required at

Evaporation

to limited

evaporation

treatment facility;

locations;

environmentally

initially

benign process; no

developed for

hazardous waste

conventional

material handling;

oil and gas

relatively inexpensive

waste handling

per-unit treatment cost

Disadvantages

Limitations

Relative Cost

Requires frequent

May require

High initial

maintenance; produces

pretreatment;

capital

concentrated brine waste

temperature

investment cost;

stream; treated water

sensitive—operates

high per-unit

quality may exceed

in 50 to 95° F

treatment cost;

needs; substantial energy

range; significant

waste stream

requirement; may require

infrastructure,

disposal cost

membrane replacement;

relatively immobile

turnkey operation;

requires large volumes to

be cost effective

No mobility of treatment

Wastewater

High initial

facility; often requires

storage ponds

capital cost for

hauling water long

and basins may

land acquisition

distances; requires large,

be hazardous

and basin

dedicated land area; only

to waterfowl;

construction;

effective in subfreezing

may require

relatively

environments, for

canopy screening;

high per-unit

limited time periods;

requires access to

treatment cost

requires full-time onsite

disposal facility

management when in

for concentrate;

operation

unpredictable

process timing

Phyto-remediation

No evidence

Selective

Utilizes naturally

Zeolites require

Technology has

Minimal capital

of large-scale

removal and/

occurring mineral

initial conditioning

not been tested

and equipment

commercial

or replacement

adsorbent; no

to remove sodium;

on water qualities

costs; low per-

use; primarily

of sodium

hazardous waste

flushing and periodic

found in San Juan,

unit treatment

used on

using cation

material handling;

replacement required;

Raton, Uinta, and

cost

experimental

exchange

minimal capital

produces waste stream;

Piceance basins;

(if zeolites are

or trial basis

aluminosilicates

investment; suitable

multiple engineered

questionable

ever applied at

(naturally

zeolite deposits occur

water treatment steps

effectiveness with

larger scale, they

occurring

within Powder River

involved; requires large

saline-brackish

may incur high

mineral

Basin; concept well

operational footprint and

waters; efficiency

initial capital

deposits)

known

extensive water storage

of sodium

costs, similar to

and handling

removal limited

ion exchange)

by specificity of

zeolite

Extensive

Consumptive

Utilizes natural and

Limited or no

No net long-

Ranges from

wetlands have

water use

constructed wetlands

effectiveness for salt or

term beneficial

none to extensive

evolved in

and selective

as water treatment

sodium removal; potential

water treatment

if wetlands or

Wyoming due

removal of

mechanism; no

evapoconcentration

in context of

plant community

to discharges

elements by

energy input required;

of salts; consumes

CBM produced

construction

and seeps;

plants

no hazardous waste

water; requires large

water treatment;

required;

limited direct

material handling;

operational footprint;

functional benefits

only per-unit

or intentional

no waste stream;

has potential to

may be temporally

treatment cost is

construction

environmentally

enhance invasive plant

limited

water delivery

or use

benign; enhanced

species and ecological

wildlife/waterfowl

community change;

habitat

nonsustainable in

absence of water; may

require periodic flushing

NOTE: Unless stated, technologies summarized in table do not provide treatment or control for bacteria.

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