A sulfur-limestone bioretention system for stormwater treatment: Nitrogen removal performance and microbial community

A lab-scale sulfur-limestone based bioretention system with a submerged zone was used to remove nitrate-nitrogen (NO₃^--N) from stormwater. The results indicated that denitrification mainly occurred during the first 5 d of drying period. With the NO₃^--N concentration in the influent increasing from 20 to 50 mg/L, after 5 d of drying period 93.99-97.26% NO₃^--N was removed, and the effluent sulfate (SO₄^2-) concentration ranged from 170.28 to 359.87 mg/L. When the NO₃^--N content in the influent was lower than 30 mg/L, the effluent SO₄^2- concentration met the Chinese Quality Standard for Ground Water (GB/T 14848-2017). Compared with the woodchips bioretention, there was no organic matter leakage problem. Sulfur autotrophic denitrification process followed first-order kinetic model, and the reaction kinetic parameters (k) were 0.7392-1.1472 d^-1. The dominant genera in the submerged zone were Thiobacillus and Halothiobacillus (>63.69%) which participated in the sulfur autotrophic denitrification process.