Efficient removal of nitrate under low temperature is challenging because of the reduction of the microbial activity. This study successfully explored the promotion on the performance of denitrification utilizing the immobilized biochar in biofilters under low temperature (6 ± 2 °C). The results showed that the immobilized biochar increased the denitrification rate by 76.8% and decreased the nitrous oxide emissions by 82.5%. Mechanistic studies revealed that the immobilized biochar increased the activities of the denitrifying enzymes and three enzymes involved in glycolysis. Furthermore, the immobilized biochar elevated the activity of the electron transport system by 31.8%. Finally, structural equation model explained that the increase of nitrate reductase activity was a crucial factor to enhance the total nitrogen removal efficiency in biofilters with immobilized biochar. Overall, the use of immobilized biochar can be a novel strategy to enhance nitrogen removal and reduce greenhouse gas emissions in biofilters under low temperature.

Beijing Capital Eco Environment Protection Group Co Ltd Beijing 100044 China; Sichuan Shuihui Ecological Environment Treatment Co Ltd Neijiang 641100 Sichuan Province China

Dapartment of Engineering Westlake University Hangzhou 310024 Zhejiang Province China

Faculty of Environmental Sciences Czech University of Life Sciences Prague Kymýcká 129 16521 Praha 6 Czech Republic

Key Laboratory of the Three Gorges Reservoir Region's Eco Environment Ministry of Education Chongqing University Chongqing 400045 China; College of Environmental and Ecology Chongqing University Chongqing 400045 China

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