High−saline and long−term treatability of industrial wastewater by AnOMBR using organic and inorganic draw solutions

Abstract

Less costly to AnMBR, anaerobic osmotic membrane bioreactor (AnOMBR) proceeds water and energy−efficient progresses within green and cleaner technologies. Long−term effectively operation of AnOMBR in high salinities due to salt accumulation is of the greatest priority, accompanied with a cost−performance efficient and non−inhibitory draw solution (DS) usage. Operational stability of AnOMBR in industrial wastewater treatment was studied at 30 mS/cm using the most favorable organic and inorganic DS within 29 DSs in our prior work, namely HCOONa and CaCl2. Osmotic and microbial yields during unintervented operations were lost due to severe salt stress and membrane biofouling. With a virgin membrane replacement, removal efficiencies, water and salt flux selectivity were partially restored, but the AnOMBRs turned towards collapse due to microbial activity lost. Therefore, sludge inoculation was applied and improved all AnOMBR performances to levels so close to before losses with 78 ± 3 % COD and 98.3 ± 0.6 % PO43-–P, 0.44 ± 0.2 L CH4/d excluding NH4+–N of 44 ± 10 %. It was designated that reverse salt passage for both the DS was responsible for approximately two-thirds of in-reactor salt build-up during stable AnOMBR operations. Statistical analysis results of the AnOMBR system for HCOONa and CaCl2 showed that statistical significances of performances in treatments with both DSs were from moderate to strong evidence levels. Microbial diversity increased by salt accumulation, and archaeal community differentiated. HCOONa promoted hydrogenotrophic halotolerant methanogenic archaeas, but not by CaCl2. Biofilm formed predominantly by biomass, Na+/Ca2+−bound biopolimers and inorganic precipitates provided bioactively better C, N, and P exhaustions in more porous and thicker secondary membrane layer by HCOONa. Beyond a virgin membrane replacement and sludge inoculation, an AnOMBR can be efficiently operated by sludge acclimation to high salinities, finest membrane clean-up, and even fabrication of FO membrane with the integrated nano-structured novel membranes such as including silver, nanofibers, graphene oxides etc.