A Combination of an Anaerobic Baffled Reactor with Membrane Filtration for Decentralised Wastewater Treatment

This paper presents the performance of a laboratory-scale anaerobic baffled reactor (ABR) with a combined membrane filtration polishing step. The plant treated a synthetic blackwater comprised of a faecal and urine slurry obtained from ventilated improved pit latrine (VIP) toilets. Feed to the system was kept constant at 2 000 mg COD/L with COD, TS and VS removal efficiencies of 81, 24 and 20% obtained through the ABR. Two effluent polishing systems were investigated: a hollow-fibre system that housed Polymem modules and a flat-sheet system that housed Kubota and locally-produced fabric modules. Membranes were operated in the dead-end mode under ultra-low pressures using a hydrostatic pressure head (less than a metre). Fouling behaviour differed with the type of filtration process despite the same feed characteristics. Effluent filtration with the Polymem module showed that the flux did not reach a stabilisation period with severe fouling occurring after 8 d. Membrane fouling was largely reversible with the fouling layer easily removed by a simple tap water wash. In contrast, effluent filtration with Kubota and fabric membranes resulted in a period of low stabilised flux (˜0.5 L/m².h) at ultra-low pressures with flux independent on the TMP used. Kubota modules exhibited a similar performance to fabric ones but were able to produce slighter higher fluxes after prolonged filtration. Membrane fouling in both flat-sheet module types was irreversible with a gel-like layer forming during filtration. The difference in hollow-fibre and flat-sheet modules may be due to a number of factors, such as pore size and the manufacturing process used to prepare membranes. Through deductive investigations, it was concluded that the fouling constituents in the effluent may be colloidal and/or soluble in nature.