USING MEMBRANES FOR RECUPERATIVE THICKENING OF ANAEROBICALLY DIGESTING SLUDGE

This paper will report the observed flux rates and cleaning requirements of two membrane systems coupled to an anaerobic sludge digestion pilot. This study was the second of two pilot projects designed to increase the processing capacity of municipal anaerobic sludge digesters.The first project analyzed the impact of shear on biomass activity in anaerobic sludge digesters. It was found that biomass activity did increase at increasing shear rates. However, it was also found that certain thickening polymers could limit the achievable increase in biomass activity. In order to circumvent this process limitation, alternate thickening methods not depending on thickening polymers were being considered. Membranes seemed to fit the bill, but it wasn't clear how well sludge might thicken in the absence of polymers. It was decided to analyze the membrane thickening concept in a second pilot study.The aim of the second study was to investigate the application of membranes for recuperative thickening during anaerobic sludge digestion rather than for thickening of raw sludge prior to anaerobic sludge digestion. This pilot project was carried out at our facility in Camden, New Jersey using non-thickened mixed primary and secondary sludge from the Gloucester County Utilities Authority (GCUA) in Paulsboro, New Jersey. The performances of two membrane systems were evaluated during the course of this study. One of the membrane systems was an oscillating cross flow system with Teflon sheet membranes and the other a tubular cross flow system with a membrane of titanium oxide sintered onto stainless steel. By operating the digester and one of the membrane systems for an extended period of time we hoped to gain insight into the longevity of the membrane system when treating a dirty substrate such as municipal sewage sludge.