Effect of intermittent operation and shunt wastewater on pollutant removal and microbial community changes in subsurface wastewater infiltration system

Abstract

Subsurface wastewater infiltration system (SWIS) is widely used in the treatment of rural domestic sewage. However, the nitrogen removal effect is unsatisfactory. In this study, laboratory-scale SWIS was built, and the nitrogen removal capacity of the system was optimized by a combination of intermittent operation and the shunt method. The optimal total nitrogen (TN) removal rate (56.53%) is obtained when the wet-dry ratio (Rwd) is 1:2 and the shunt ratio is 3:1. The optimal ammonia nitrogen (NH4+-N) removal rate (54.97%) is obtained when Rwd is 1:3 and shunt ratio is 2:1. In addition, SWIS achieved a good COD removal rate (>75%) and TP removal rate (>95%) during the whole operation stage. Proteobacteria, Acidobateria and Bacteroidetes are high abundance phyla in SWIS. Bacteroidetes, Chloroflexi and Nitrospirae associated with nitrogen removal are abundant at the shunt ratio of 2:1 and 3:1. At the genus level, Bosea, Bradyrhizobium and Phenylobacterium were functional genera associated with denitrification, enriching the substratum of SWIS at shunt ratios of 1:1, 2:1 and 3:1. Nitrogen (N) forms and ORP analysis showed that under the appropriate shunt ratio and Rwd, the SWIS matrix has a suitable redox microenvironment, and thus creates a well-defined nitrification area and denitrification area. This research provides a reliable theoretical basis for the construction and operation of SWIS in rural areas.