Performance and microbial analysis of a fluidized bed membrane bioreactor operated in the partial nitrification and anammox (PN/A) mode for polishing anaerobically treated effluent to industrial discharge standard

This study evaluates the performance and microbial dynamics of an ORP-controlled fluidized bed membrane bioreactor impregnated with partial nitrification and anammox culture (FMBRPN/A) for polishing the low COD/ NH4+ anaerobically treated effluent of the seafood processing industry. Results showed that the highest average removal of COD and total nitrogen were 68.6% and 75.0% at COD/NH4+ 0.44 and 0.33, respectively. Heterotrophic denitrification accounted for only 3.0-7.1% of the overall nitrogen removals at COD/NH4+ 0.33-0.55. A low nitrite oxidation rate observed indicated that almost all NO3 - came from anammox reactions. Data on ammonia oxidation rate, nitrite oxidation rate, and anammox nitrogen removal rate pointed to the competitive advantage between heterotrophic and nitrifying/anammox consortia at higher and lower COD/NH4+ ratios. When salinity threat at 5 g/L NaCl in the influent was imposed to FMBRPN/A, nitrogen removal was almost completely eliminated but quickly recovered to 25.5% as organic removal was not affected. Activities of the nitrogenous autotrophic organisms and heterotrophic microbes were strongly dependent on the presence of organic and salinity in the wastewater. Microbial analysis of biofilm formed on the membrane surface showed a significant difference in the succession of dominant bacteria during the experiments. Next Generation Sequencing indicated the dynamic shifting proportions of ammonium oxidizing bacteria (AOB), nitrite oxidization bacteria (NOB), denitrifying bacteria (DNB), and anammox bacteria (AMX) ranging from 49.4% to 64.2% at various COD/NH4+ ratios, which suggested their syntrophic relationship. Superior membrane retention of FMBRPN/A for heterotrophic and slow-growing autotrophic cells facilitated system stability and efficiency to meet the industrial effluent standard.

Automated summary

This study evaluated the performance and microbial dynamics of an ORP-controlled fluidized bed membrane bioreactor (FMBRPN/A) for treating low COD/ NH4+ anaerobically treated effluent from the seafood processing industry. Results showed high removal rates of COD and total nitrogen, with heterotrophic denitrification accounting for only a small percentage of nitrogen removal. Salinity threat had a significant impact on nitrogen removal but did not affect organic removal. Microbial analysis revealed a shift in dominant bacteria in the biofilm on the membrane surface, indicating a symbiotic relationship between AOB, NOB, DNB, and AMX bacteria. The superior membrane retention of FMBRPN/A facilitated system stability and efficiency.