Abstract:
Reverse solute transport (RSF) of ions inside the bioreactor from the draw solution is the main problem of forward osmosis (FO). This RSF is significantly reduced when fertilizers with anions of larger hydrated diameter are used. Performance of three selected 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). For effective recovery of draw solutes and production of clean water, a direct contact membrane distillation (DCMD) setup was integrated with FO-MBR setup to form a hybrid (FOMBR-MD) system. Results demonstrated that the MAP significantly reduced the salinity buildup (0.113 g/m2/hr (gMH)) inside the bioreactor, in comparison with SOA (0.568 gMH) and MKP (1.17 gMH), during FO operation. At constant molar concentration, SOA showed the highest initial water flux of 2.5 LMH followed by MKP (2.11 LMH) and MAP (1.97 LMH) during FO-MBR operation. Furthermore, MKP exhibited the shortest filtration run of 12 days due to increased salinity buildup inside the bioreactor which led to the rapid flux decline, and SOA showed relatively prolonged filtration runs followed by MAP of 17 and 15 days, respectively. It was found that MKP and SOA exhibited inhibitory effects on the mixed liquor characteristics in terms of biomass growth, particle size distribution and sludge filterability in contrast with MAP. Approximately 98±1% removal of COD and total phosphorus (TP) was achieved for all three fertilizers because of the synergic effect of dual barrier membranes. Only 90±2% removal of NH4+-N was found in case of ammonium-based fertilizers (i.e. SOA and MAP), while 99±1% removal was attained in case of MKP as draw solute. Based upon these findings, MAP was found to be the most viable draw solute for (FO-MBR) considering low RSF, moderate flux, prolong filtration cycle, high biomass growth, and treatment performance.
