Treatment of Simulated Coalbed Methane Produced Water Using Direct Contact Membrane Distillation

Expolitation of coalbed methane (CBM) involves production of a massive amount saline water that needs to be properly managed for environmental protection. In this study, direct contact membrane distillation (DCMD) was utilized for treatment of CBM-produced water to remove saline components in the water. Simulated CBM waters containing varying concentrations of NaCl (1, 20, and 500 mM) and NaHCO₃ (1 and 25 mM) were used as feed solutions under two transmembrane temperatures (Δ40 and 60 °C). In short-term distillation (~360 min), DCMD systems showed good performance with nearly 100% removal of salts for all solutes concentrations at both temperatures. The permeate flux increased with the feed temperature, but at a given temperature, it remained fairly stable throughout the whole operation. A gradual decline in permeate flux was observed at Δ60 °C at high NaHCO₃ concentration (25 mM). In long-term distillation (5400 min), the presence of 25 mM NaHCO₃ further decreased the flux to 25%–35% of the initial value toward the end of the operation, likely due to membrane fouling by deposition of Ca-carbonate minerals on the pore openings. Furthermore, pore wetting by the scalants occurred at the end of the experiment, and it increased the distillate conducitivity to 110 µS·cm⁻¹. The precipitates formed on the surface were dominantly CaCO₃ crystals, identified as aragonite. View Full-Text