Kitchen waste composting leachate stimulates endogenous simultaneous nitrifying and denitrifying pathways in WWTPs

Kitchen waste CL serves as an abundant source of organic compounds for WWTPs. This study examines the impact of CL on nitrifying and denitrifying processes through SBR. Results indicate that CL enhances nitrogen removal efficiency, achieving rates of approximately 95 %, and alters microbial communities associated with denitrification, particularly with a mixing ratio of up to 1.5 %. The effects of specific carbon components-NaAc, SBA, and LA-were analyzed on anaerobic denitrification and HN-AD pathways. Anaerobically, NaAc and SBA supported Stutzerimonas balearica, lacking N₂O reduction ability, while SBA suppressed Stenotrophomonas acidaminiphila with narG and norB genes. LA favored Stutzerimonas stutzeri, promoting NO₂^- reduction to N₂. Aerobically, LA boosted napA, norB, and nosZ gene abundances, facilitating NO₃^- reduction, whereas NaAc and SBA elevated nirS/K levels. Unlike traditional nitrification-denitrification methods, a novel HN-AD pathway was suggested, driven by heterotrophic nitrification and denitrification via CL. These insights reveal the potential of CL as an external carbon source for WWTPs, optimizing nitrogen management and minimizing greenhouse gas emissions.