Anaerobic Membrane Bioreactors (AnMBR) For WAS Digestion: Tubular Versus Hollow Fiber (HF) Membranes

Anaerobic digestion is a common technology that is employed for reducing the quantity of solids that are generated in wastewater treatment while also generating a biogas that can be employed as an alternative fuel thereby increasing the sustainability of these facilities. However, hydrolysis processes typically limit the rate of anaerobic digestion, particularly of secondary sludges, and hence extended solids residence times in digestion are required. The extended solids residence times lead to large digester volumes with substantial capital costs and operating costs associated with heating, mixing and pumping. The implementation of anaerobic membrane bioreactors (AnMBRs) for sludge digestion can decouple solids residence times from hydraulic residence times thereby facilitating a substantial reduction in digester volume while maintaining good solids destruction. This paper presents the results of pilot scale studies that examined the use of tubular and hollow fiber (HF) anaerobic membrane bioreactors (AnMBRs) for anaerobic digestion of waste activated sludge (WAS). The results indicate that both membrane digesters showed comparable CODT and VS removals of 47.6 and 49.1% respectively while maintaining a throughput that was 2 times that of the control digester. The average fluxes for the neutral and negative tubular membranes were 32.3±0.8 and 38.6±2.1 LMH when operated at a TMP of 30 kPa. The HF membranes were operated at a constant flux of 11±0.7 LMH and the average TMP was less than 10 kPa.