Enhanced nutrient removal of agricultural waste-pyrite bioretention system for stormwater pollution treatment

Pyrite as filler applied to bioretention cells has the potential for simultaneous nitrogen and phosphorus removal, but its low electron supply rate cannot adapt to the demand for nitrogen and phosphorus removal under high rainfall intensity and continuous rainfall conditions. In this study, novel pyrite-based bioretention cells with agricultural waste amendment (corn cobs, rice husks, wood chips) were developed, and the pollution removal of each cell was evaluated under simulated complex rainfall conditions. The bioretention cell amended with woodchips achieved significantly higher efficiency and stability for dissolved nutrient removal compared with the pyrite bioretention cell. Its average removal efficiency of nitrate nitrogen, total nitrogen, and phosphate phosphorus was 69.39%, 45.60%, and 60.01% higher than that of the control group. The average chemical oxygen demand (COD) and total iron (TFe) concentrations in the effluent were slightly higher than those from the pyrite bioretention cell but were significantly lower than those from the corn cob and the rice husk-pyrite bioretention cell. Microbiological analysis revealed that the addition of woodchips significantly increased the relative abundance of Thiobacillus (the main functional genus of autotrophic denitrification) and Thauera (the main functional genus of heterotrophic denitrification) in the bioretention cell to 25.17% and 3.06%. The results indicated that woodchips promoted the proliferation of both heterotrophic and autotrophic microorganisms, therefore enhancing the nitrogen removal efficiency of mixotrophic denitrification.