In-situ utilization of nitrogen-rich wastewater discharged from a biotrickling filter as a moisture conditioning agent for composting: Insights into nitrogen transformation behavior and microbial mechanism

An NH₄⁺–NO₂^–-rich wastewater discharged from a composting-biotrickling filter coupled system can be reused as a composting moisture adjustment agent. To investigate the impact mechanism of reuse, NH₄⁺–NO₂^–-rich wastewater, NH₄⁺-rich wastewater, NO₂^–-rich wastewater, and distilled water were added into the composting (i.e., AMN, AAN, ANO2, and ADW groups). Results show that compost of all groups met the corresponding criteria for stabilization, humification, and non-phytotoxicity of mature compost. AMN increased organic-N and NO₃^–-N content and reduced NH₃ emissions, like AAN or ANO2, and avoid stimulating N₂O emission in AAN and ANO2. Furthermore, LEfSe analysis of microorganisms revealed that AMN reduced NH₃ emissions and increase organic-N content probably due to the inhibition of Alphaproteobacteria by ammonium, and increased nitrate content probably due to the stimulation of Aquamicrobium by nitrite. The avoided N₂O emission is probably due to a negative synergistic effect on the stimulation from ammonia and nitrite to denitrifying bacteria (eg., Sphingobacteriaceae).