Metagenomic analysis revealed the mechanism of extracellular polymeric substances on enhanced nitrogen removal in coupled MABR systems with low C/N ratio containing salinity

Abstract

A combined membrane-aerated biofilm reactor (MABR) was conducted to treat various C/N ratios with saline wastewater. The influence of C/N on nitrogen removal property, extracellular polymeric substances (EPS) features, bacterial community and relevant functional genes were investigated. Fourier-transform infrared spectrum (FTIR), three-dimensional exaction and emission matrix (3D-EEM) fluorescence spectra and metagenomics analysis were conducted to study the mechanism of EPS for enhanced nitrogen removal at low C/N ratio. The results showed that TN removal rate of the whole MABR system were 73.21%, 69.51% and 67.04%, respectively, with the C/N ratio of 6, 4.5 and 3. MABR-2 biofilms secreted more EPS under low C/N and high-salinity conditions to maintain intracellular and extracellular osmotic pressure balance and to participate in cellular metabolic processes. Meanwhile, under the stimulation of low C/N, MABR-2 system with low influent loading was in a “starvation state”, thus EPS could be utilized by the biofilm of MABR-2 system as carbon source to enhance nitrogen removal. Besides, metagenomics analysis showed that aerobic denitrification and dissimilatory nitrite reduction to ammonia (DNRA) were dominant nitrogen removal pathways in MABR-2 system at low C/N ratio. EPS might participate in related metabolic processes in the electron donors and energy production processes as well as the electron transfer pathways in denitrification system. This work provided a feasible practical application scheme for the enhanced TN removal of low C/N ratio containing salinity.