Sustainable sewage treatment plants - application of nanofiltration and ultrafiltration to a pressurized bioreactor

Abstract

Based on earlier studies and experiences the Institute of Sanitary Engineering, Water Quality and Waste Management at the University of Stuttgart has developed a new technology to purify wastewater to a quality suitable for reuse as industrial water. This technology consists of a pressurized bioreactor under 3 bar with an ultrafiltration unit for sludge retention coupled with a nanofiltration unit. The concentrate retained in the nanofiltration is fed back to the bioreactor resulting in an enhanced biodegradability and a better quality of the effluent. The flux through the ultrafiltration membrane ranged from 100 to 200 l/(m3h); that through the nanofiltration membrane was around 0.05 l/(m3h). While attaining a very high biomass concentration (20 to 40 kg MLVSS/m3) in the bioreactor the excess sludge production is remarkably small with 0.7 to 1.0% of the influent COD.