Low-energy advanced wastewater treatment using submerged nanofiltration

Abstract

The use of submerged nanofiltration (NF) membranes in wastewater treatment is an emerging process that produces high-quality recycled water with low energy consumption. This study aimed to identify the potential of coupling anaerobic digestion with this low-energy advanced wastewater treatment using submerged NF membranes. The direct NF of primary wastewater effluent using four types of commercial NF membranes resulted in progressive membrane fouling over 4 d. However, almost all the foulants contributing to hydraulic loss were removed by one-swipe sponge cleaning. This indicated that the major foulants were generally deposited on the membrane surface during direct NF. The membrane fouling speed varied during the long-term test depending on the feed wastewater quality. Although the transmembrane pressure increased by up to 50 kPa in every filtration cycle (4–7 d), sponge cleaning removed all the membrane foulants, resulting in >30 d of operation without chemical cleaning. The NF concentrates (four times concentrated wastewater) were then used for biogas production in an anaerobic digester. The volume of biogas formed from the NF concentrates sufficiently compensated for the energy consumption of direct NF. This study realized a low-energy advanced wastewater treatment utilizing NF concentrates that can also be used for biogas formation.