Continuous municipal wastewater up-concentration by direct membrane filtration, considering the effect of intermittent gas scouring and threshold flux determination

Abstract

Municipal wastewater is recognized as having a high amount of biodegradable matter which is not easily hydrolyzed through anaerobic treatments in cold climate countries. Under proper operating conditions, the direct membrane filtration (DMF) appears to be a feasible technology, capable of efficiently separating and concentrating the primary wastewater for subsequent anaerobic digestion under mesophilic conditions. The long-term operation of a municipal wastewater concentration process was proved feasible with intermittent gas scouring (40 s of operation followed by a pause of 3.5 min) and permeate backwash. Operating at 12.7 L/m2.h feed with medium strength wastewaters, a permeate stream below the discharge limit was obtained, and the resulting concentrate streams presented levels of between 19,000 and 54,000 mg/L of COD. An estimated energy balance pointed to the self-sufficiency of the process by allowing for an energy production of 0.19 kW h/m3 through the anaerobic digestion, while the power consumption for the gas scouring and pumping resulted in 0.15 kW h/m3. Experiments demonstrated that the threshold flux for a wastewater filtration is highly influenced by the gas scouring velocity. The operation performed with 32.9 gTSS/L of primary concentrated wastewater indicated that the threshold fluxes increase by more than 300 % through increasing the gas scouring velocities from 0 to 30.6 m/h.