Maximum Influent Salinity Affects the Diversity of Mineral-Precipitation-Mediating Bacterial Communities in Membrane Biofilm of Hybrid Moving Bed Biofilm Reactor-Membrane Bioreactor

Two hybrid moving bed biofilm reactor-membrane bioreactors were used for the treatment of variable-salinity influent wastewater with maximums of 4.5 and 8.5 mS cm−1 electric conductivity. Operational conditions of the bioreactors were 6 h hydraulic retention time and 2500 mg L−1 total solids. The membrane operated in a cycle of 9 min draw-1 min backwash and at 23.6 L h−1 m−2 flux rate. Membrane biofilm was collected from both systems and cultured in growth media for precipitation of carbonate and phosphate minerals, yielding only Bacillus stratosphericus for the 4.5 mS cm−1 scenario and Bacillus stratosphericus, Bacillus toyonensis, Microbacterium esteraromaticum, Comamonas testosteroni, and Janibacter meloni for the 8.5 mS cm−1 scenario. Scanning electron microscopy and X-ray analysis showed similarities in morphology and composition for the carbonate crystals from both salinity conditions and differences for the phosphate minerals. Study of the bacterial community of membrane biofilm and mixed liquor showed close similarities between them for the same salinity conditions, with both dominated by genera Rhodanobacter, Chujaibacter, and Thermomonas.