Use of hollow fibre membrane contactors to remove dissolved gases from effluents of UASB reactors treating sewage after its conditioning with dynamic membrane filtration

Abstract

Dissolved gases in the effluent of anaerobic reactors, such as dissolved methane (D-CH4) and sulphide (S2−), are a drawback for anaerobic-based sewage treatment plants. Hollow fibre membrane contactors (HFMCs) have been tested for the removal of these compounds, and this paper evaluated a novel configuration with pressurised dynamic membrane modules (PDMMs) for conditioning an anaerobic effluent (from UASB reactor fed with sewage) as a means to reduce HFMCs clogging and fouling. Three PDMMs were used for the anaerobic effluent conditioning before two types of HFMCs (dense and microporous membranes). An automated backwash with a tap water cleaning protocol complemented with a chemical cleaning protocol (NaOH and citric acid) was applied for fouling control. The microporous HFMC could not maintain a stable performance (D-CH4 and S2− removal drop of 30 % and 40 %, respectively, in 10 days of operation), arguably due to membrane wetting, meanwhile the dense HFMC showed a more stable behaviour (removal efficiencies close to 100 % and 90 % for S2− and D-CH4, respectively in >30 days). The water backwash removed an important fraction of the entrapped organic solids. Meanwhile, the NaOH cleaning was efficient in removing inorganic compounds. Citric acid contributed to the removal of calcium and phosphate.