Mitigation of membrane fouling in a seawater-driven forward osmosis system for waste activated sludge thickening

Abstract

Abstract Forward osmosis is a promising technology for waste activated sludge thickening. It would be desirable if the membrane fouling could be controlled so that the operation for waste activated sludge thickening can be more sustainable. In this study, the role of polyaluminium chloride conditioning in improving performance of forward osmosis for waste activated sludge thickening and its effects on fouling mitigation were investigated. The results show sludge can be concentrated up to 52.5 g L−1 at the end of each operation cycle. In comparison with raw waste activated sludge, sludge thickening efficiency and water recovery flux of forward osmosis were greatly enhanced by polyaluminium chloride conditioning. Polyaluminium chloride facilitated the reduction of sludge capillary suction time, extracellular polymeric substances content, loosely bound extracellular polymeric substances in particular, which had significant impact on mitigating membrane fouling. As a result, long-term stable operation of sludge thickening without substantial flux decline was successfully obtained. In addition, seawater brine which holds high osmotic pressure could be an alternative draw solution.