Study of pyrite based autotrophic denitrification system for low-carbon source stormwater treatment

Improving the nitrogen removal capacity of stormwater runoff has been the main research direction of bioretention systems in recent years. Heterotrophic denitrification in traditional bioretention systems was often used, but insufficient carbon sources in the runoff limit it. In this study, two bioretention systems using natural pyrite and zeolite as substrates were constructed to explore the feasibility of pyrite-based autotrophic denitrification in bioretention for nitrogen removal. During eight months of operation at natural conditions, the results showed that pyrite had no negative effects on the removal of NH4+-N, but enhanced denitrification in the bioretention system with no or low carbon source in the influent. Pyrite based bioretention system (PBS) can adapt to low temperature and irregular wet and dry alternation. The average NH4+-N, TN, and TP removal efficiency of PBS during eight months were 87.6%, 89.3 %, and 81.6%. The average NH4+-N, TN, and TP removal efficiency of zeolite-based bioretention system (ZBS) were 98.7 %, 47.1 %, and 47.5 %. By-products (SO42- and Total iron) of PBS were all at an acceptable level. The dominant genera in PBS were Denitratisoma (3.6 %), Ellin6067 (2.7 %), Thiobacillus (2.6 %), Thauera (2.1 %), CL500-29 marine group (1.8 %), Sulfuritalea (1.7 %), Subgroup 10 (1.4 %). Genera Thiobacillus, Thauera, and Sulfuritalea were highly related to autotrophic denitrification. Moreover, genera Denitratisoma was highly related to heterotrophic denitrification. This study shows that pyrite could be a promising eco-friendly substrate in the bioretention system for nutrient removal.