Evaluation of silica fouling for coal seam gas produced water in a submerged vacuum membrane distillation system

Abstract This study assessed the formation and the effect of membrane fouling in membrane distillation in treating coal seam gas produced water that contains high silica concentration (200 ppm) on membrane performance. The effects of interactions of polyvalent ions (magnesium and calcium) with carbonates and silica on membrane fouling in a submerged vacuum membrane distillation (VMD) system were evaluated. Significantly better performance was observed with the feed contained silica with gradual flux decrease to 75% of the value achieved with pure water over 80 h, than that in the feed without silica. The precipitated crystals on the membrane surface were mostly calcites in the MD tests with magnesium silicate co-precipitation instead of aragonites found in the non-silica feed. The precipitated species in the solution and on the membrane surface agrees with the estimation of saturation index in the feed solution at the relevant temperature and pH values. The foulant on membrane surface in the submerged VMD process was easily removed by a simple cleaning protocol through immersion of the module in 0.32 wt.% hydrochloric acid for 10 min at 24 h interval in the treatment of silica rich feed, with sustainable performance for at least 78 h.