Passive remediation of coalbed natural gas co-produced water using zeolite
Coalbed natural gas (CBNG) co-produced waters can contain sodium (Na+) concentrations that may be environmentally detrimental if discharged to receiving bodies of water or applied to land surfaces. A field demonstration and companion laboratory studies were conducted to evaluate the use of a Bear River zeolite (BR-zeolite) for mitigating impacts associated with Na+ in CBNG waters. Bench-scale kinetic and adsorption isotherm studies were performed to determine both the rate and extent of sodium Na+ adsorption and assess the effects of bicarbonate (HCO3-) and chloride (Cl-) anions. Results of these studies showed that the adsorption of Na+ on BR-zeolite followed the Langmuir adsorption model with maximum adsorption equal to 21 and 18 g Na+/kg zeolite with 0.0012 and 0.0006 L/mg Langmuir coefficients (KL) for sodium bicarbonate and sodium chloride, respectively. The kinetics study indicated that the sorption of Na+ was inversely related to the size of the zeolite particles with significantly greater adsorption for smaller particles. The field demonstration evaluated the effectiveness of BR-zeolite for mitigating infiltration losses from Na+ in CBNG waters. The field site utilized 12 open boreholes, each installed to a depth of approximately 1.8 m. Each borehole was lined with a 3.0 m long, 15 cm diameter schedule 40 PVC pipe and fitted with an automatic data logging pressure transducer for measuring water levels over time. The BR-zeolite was found to mitigate much of the deleterious effect that high sodium adsorption ratio (SAR = 27 (mol/m3)1/2) CBNG co-produced water had on soil permeabilities.