In order to clarify effect of magnetic biocarriers on the performance of MBBR at low temperatures, the microbial diversity, community structure, functional characteristics, and nitrogen metabolism of biofilm in the reaction system were investigated. The results indicated that MBBR with magnetic biocarriers had a better pollutant removal efficiency, with the average removal rates of NH4+-N and TN being 16.2% and 12.1% higher than those in the control group (commercial biocarriers), respectively. Illumina high-throughput sequencing analysis showed that higher diversity and richness of the bacterial community was established in the biofilm of magnetic biocarriers. There were obvious differences in microbial community structure of biofilm between the two biocarrier duos to bacterial magnetic susceptibility. The relative abundances of nitrifying bacteria (e.g., Nitrosomonas and Nitrospira) and denitrifying bacteria (e.g., Sphaerotilus and Zoogloea) were increased in the magnetic biocarriers. Functional prediction analysis with PICRUSt2 showed that the microorganism of magnetic biocarriers had a better total gene function expression level, which was significantly more increased than commercial biocarriers in gene-representing signal transduction mechanisms and intracellular trafficking, secretion, and vesicular transport. Furthermore, most of the abundances of nitrogen metabolism genes were raised in the biofilm of magnetic biocarriers (e.g., genes amo and hao, were responsible for nitrification, and genes nap and nor, which were responsible for denitrification). Magnetic biocarriers increased biofilm potential for denitrification at low temperatures. Our results explained the difference in performance between the two reactors from microbiology and provided the theoretical basis for magnetic biocarrier-enhanced performances of MBBR at low temperatures.
Keywords: biofilm; gene function prediction; high-throughput sequencing; magnetic biocarrier; microbial community structure.