Biofouling control of a forward osmosis membrane during single-pass pre-concentration of wastewater.

Pre-concentration of wastewater using a forward osmosis (FO) membrane prior to processing by an anaerobic digester can enhance biogas production. However, biofouling caused by microbes in wastewater remains a challenge. The study aimed to evaluate the efficacy of chloramination in mitigating the biofouling of an FO membrane during a single-pass concentration of primary wastewater effluent. Pre-disinfection at a chloramine dose of 22-121 mg/L successfully alleviated membrane fouling. Bacterial cell counts in the feed and concentrate showed that most of the bacterial cells in the wastewater were trapped on the membrane surface or spacer. The FO membrane surfaces in non-chloraminated/chloraminated systems were fully-covered by intact/damaged bacterial cells, respectively, indicating that chloramination effectively mitigated biofouling. However, due to high permeate-recovery and low cross-flow velocity in a single-pass concentration process, organic fouling on the membrane surface (and possibly on the interior wall of the membrane-pores) appeared to cause a gradual reduction in permeate-flux. This study demonstrated successful biofouling control using chloramination during a single-pass and high-recovery pre-concentration of primary wastewater effluent.