DIRECT MEMBRANE FILTRATION (DMF) OF MUNICIPAL WASTEWATER USING A BIOFILM PROCESS AS A PRE-TREATMENT

Abstract

 Organic matter in municipal wastewater should be regarded as a resource for energy production in future wastewater management. Concentration of organic matter in municipal wastewater is necessary for application of anaerobic digestion. Direct membrane filtration (DMF) of municipal wastewater using microfiltration can easily concentrate organic matter in municipal wastewater. However, severe membrane fouling and high concentration of organic matter in treated water have been identified as problems to be solved. In this study, a biofilm process using sponge carriers was used as a pre-treatment, aiming for mitigating membrane fouling and reducing concentration of organic matter in the permeate. The pretreatment worked efficiently when water temperature was low: membrane fouling could be mitigated while recovery of organic matter was maintained. However, when water temperature was high, the pre-treatment accelerated membrane fouling in the subsequent membrane process. It was probably due to production of biopolymers in the pre-treatment process. To control the fouling caused by such biopolymers, use of chemical cleaning by oxidants (e.g., NaClO) would be effective. When the water temperature was high, the BOD concentration in the DMF permeate was reduced to 7 mg/L, which is almost same the level as that in conventional activated sludge process.