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.
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