Enhancement of denitrification by MnO₂-modified biochar under low-temperature: Performance evaluation and mechanistic...

Low temperatures significantly hinder denitrification in cold climates. In this study, MnO₂-modified biochar (MBC) was utilized to improve microbial denitrification at low temperatures. Results showed that the modification considerably raised the specific surface area, pore volume, and electron transfer capacity of biochar (BC) by 185%, 88%, and 30%, respectively. MBC significantly enhanced the TN removal efficiency of denitrifiers, reaching 3.23 mgN·gVSS^-1·h^-1. The activities of key enzymes linked to glycolysis (HK, PFK, PK) and denitrification (Nar, Nir, Nos), alongside the electron transport system activity, as well as ATP and NADH levels, were significantly enhanced. The enrichment of Acidovorax and Tolumonas indicated that microbial manganese redox cycling played a critical role in promoting TN removal. Column experiment further demonstrated that MBC improved the TN removal efficiency of the denitrification biofilter by 33%, highlighting its practical efficacy in biofilm systems. Overall, MBC presents a novel strategy for enhancing denitrification efficiency at low temperatures.