Exploring microbial drivers of DOM removals and greenhouse gas emissions in a centralized wastewater treatment plant of a large-scale coal industrial park.

Coal chemical wastewater (CCW) is commonly co-treated with domestic sewage to improve its biodegradability in centralized wastewater treatment plants (CEWWTPs). Here, microbial drivers of DOM removals and greenhouse gas (GHG) emissions were explored in CEWWTP of a large-scale coal industrial park. Five fluorescence components (C1-C5: aromatic macromolecular-like, naphthenic-like, fulvic-like, phenolic-like and tryptophan-like) and three functional groups (amine, phenolic and aromatic) were identified from DOM in CCW. C1, C2 and C4 accounting for 74.85 % of all components, were mostly degraded in anaerobic and ozone oxidation tanks. The rate of N₂O emission reached the peak (1241.76 mmol m^-2 h^-1) in the 1st anoxic tank, where removal efficiencies of all components were less 10.00 %. Based on hetero 2D-EEM/UV-COS, the varying order of DOM fractions and functional groups was amine→C5→C4→phenolic→C2→aromatic→C3→C1, suggesting that amine and phenolic be intermittently degraded along with tryptophan-like and phenolic-like, while aromatic be consecutively degraded along with fulvic-like and aromatic macromolecular-like. According to structural equation model, ORP and pH showed positive effects (β = 0.71) on bacteria, while DO exhibited an inverse effect (β = -0.70). Certainly, ORP, pH and DO were the key drivers of influencing abundance and diversity of bacteria, e.g., Zoogloea and Actinobacteria. Bacteria had indirect positive effects on GHG emissions by conventional pollutants or by DOM fractions. This suggested that organic matter decomposition by bacteria should yield CO₂ via respiration or serve as an energy source for denitrifying bacteria to produce N₂O. Hence, these findings might be conducive to identify optimal carbon sources and process conditions to balance pollutant removal efficiencies and GHG emissions.