Performance and microbial communities of different biofilm membrane bioreactors with pre-anoxic tanks treating mariculture wastewater

The performance of pollutant removals, activated sludge characteristics, and microbial communities of two biofilm membrane bioreactors coupled with pre-anoxic tanks (BF-AO-MBRs) (one using fiber bundle bio-carriers (FB-MBR) and the other using suspended bio-carriers (MB-MBR)) were compared at the salinity between zero and 60 g/L. At all salinities, three bioreactors showed good COD average removal efficiencies (> 94.1%), and FB-MBR showed the best TN removal efficiency (90.4% at 30 g/L salinity). Moreover, FB-MBR had the faster process start-up time and better salt shock resistance. At high salinities (30-60 g/L), more extracellular polymeric substances were produced by the BF-AO-MBRs to avoid the penetration of salt and protect the bacterial community. Because of the different attachment patterns of biofilms, the microbial community structure in the FB-MBR exposed to 30 g/L salinity had higher nitrite-oxidizing/ammonia-oxidizing bacteria ratio (6.44) with more abundance of denitrifiers, which contribute to higher TN removal efficiency and lower nitrite accumulation.