Performance evaluation of fertilizer draw solutions for forward osmosis membrane bioreactor treating domestic wastewater

The reverse solute flux (RSF) of draw solute ions towards the bioreactor is one of the main issues for concern during the forward osmosis membrane bioreactor (FO-MBR). This RSF can be significantly reduced with fertilizer-based draw solutes with anions of relatively large hydrated diameter. The individual performance of three such fertilizer-based draw solutes, ammonium sulfate (SOA), potassium hydrogen phosphate monobasic (MKP) and mono ammonium phosphate (MAP) was investigated in a forward osmosis membrane bioreactor (FO-MBR) integrated with direct contact membrane distillation (DCMD) process. During FO operation, results demonstrated that use of MAP significantly reduced the RSF (0.113 g/m(2)/hr (gMH)) towards the bioreactor, in contrast with that of SOA (0.568 gMH) and MKP (1.17 gMH). MKP exhibited the shortest filtration run of 12 days because of increased buildup of draw solute inside the bioreactor. On the other hand, SOA showed relatively prolonged filtration runs of 17 days, followed by 15 days for MAP. It was also found that MKP and SOA exhibited inhibitory effects on the mixed liquor characteristics in contrast with MAP in terms of biomass growth, particle size distribution and sludge filterability. Based upon these findings, MAP was found to be the most viable draw solute for the FO-MBR. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.