Full-scale operation of an integrated aerated biofilter–denitrification shallow biofilter system for simultaneous nitrogen and phosphorus removal from low-carbon domestic sewage: Influencing parameters, microbial community and mechanism

Abstract

At present the problem of not satisfying the increasingly strict emission standards in the biological treatment of domestic sewage characterized by high nitrogen and phosphorus stress has become prominent, especially under the insufficient carbon source. For the efficient treatment of low-carbon sewage, a full-scale integrated system was constructed and practically applied, which is based on a combination of an up-flow aerated biofilter and a denitrification shallow biofilter (UAB-DSB). The effects of operation parameters such as air/water ratio, hydraulic load, C/N ratio, and polyaluminum chloride (PAC) dosage on nitrogen and phosphorus removal were investigated. With the optimal parameters, the maximum removal efficiencies of chemical oxygen demand (COD), NH4+-N, total nitrogen (TN), and total phosphorus (TP) reached approximately 90%, 85%, 80%, and 92%, respectively, achieving an excellent quality effluent. Based on the water quality changes along the filter layer height, a dynamic equation for predicting NH4+-N removal was established, which can be applicable to different hydraulic loads. High-throughput sequencing analysis results indicated that the dominant bacteria genera were Longilinea, Nitrospira, and Terrimonas in UAB, while those in DSB were Longilinea, Ornatilinea, and Thauera. As proved by metagenomic analysis, the nxrA and nxrB genes encoded key enzymes in the nitrification, while narG, napA, nirS, norB, and nosZ genes were mainly responsible for the denitrification. By analyzing the spatial variations of the microbial communities and functions, the main mechanisms underlying the UAB-DSB system along the water flow direction were in turn carbon removal, ammoniation, synchronous nitrification and denitrification, aerobic denitrification, and heterotrophic denitrification.