Removal of emerging organic contaminants in a subsurface wastewater infiltration system: A preliminary study of microbial mechanism.

Subsurface wastewater infiltration systems (SWISs) have been widely used for rural decentralized wastewater treatment, but their performance in removing emerging organic contaminants (EOCs) from wastewater remains unclear. We investigated EOC removal and related microbial mechanism in an intermittently aerated SWIS operated at a hydraulic loading rate of 0.5 m/m/day under field conditions. Among the 89 analyzed EOCs covering a wide range of different physicochemical properties, seven biocides, five antibiotics, two other pharmaceutics and three herbicides were detected in the real domestic wastewater fed into the system, with concentrations ranging from 7.80 ng/L for lincomycin to 14809 ng/L for bentazone. All detected EOCs were effectively removed in the SWIS with removal efficiencies ≥ 74.5%, except that diethyltoluamide and sulfamonomethoxine were moderately removed (31.9% and 58.8%, respectively). Meanwhile, removal efficiencies ≥ 81.1% were observed for conventional pollutants, including chemical oxygen demand, total organic carbon and ammonium. The pollutant removal was mainly attributed to microbial degradation due to lack of plants, photodegradation and sorption of most detected compounds in the system. This was corroborated by the abundance of microbial communities in the SWIS substrate and their positive correlations with pollutant removal rates, such as Proteobacteria, Planctomycetes and Bacteroidetes at the phylum level and Ottowia, Defluviicoccus, Bradyrhizobium, Thiobacillus, Rudaea, Methylocystis, Reyranella, Parvibaculum and Parasegetibacter at the genus level. Therefore, this work supports SWIS as a promising technology for treating decentralized domestic wastewater containing EOCs in addition to conventional pollutants, and underscores the pivotal role of microorganisms in pollutant removal in SWISs.