Rapid start-up and microbial response strategies of an anaerobic digestion system for coal chemical wastewater treatment.

Coal chemical wastewater (CCW) contains high concentrations of difficult-to-biodegrade organic matter, which complicates the start-up and stable operation of biochemical treatment. This study designed an anaerobic biochemical system for CCW treatment. The system achieved rapid start-up and stable operation for CCW using a small amount of co-metabolism substrate. The results reveal that at a chemical oxygen demand (CODCCW) of 2500 mg/L, the biochemical system achieves a COD removal rate of 80.72 %. Moreover, the effluent total organic carbon concentration decreases to 141.44 mg/L. The removal rates of benzene series, phenolic compounds, polycyclic aromatic hydrocarbons, long-chain alkanes, and nitrogen-containing heterocyclic organic pollutants are maintained above 80 %, while effluent biodegradability is significantly improved. Although CCW causes sludge loss, it stimulates microorganisms to secrete more extracellular polymeric substances (EPS) to mitigate the adverse effects of the wastewater. Among the various EPS, loosely bound EPS (LB-EPS) plays a crucial role in rapid start-up, stable operation, and the capture and degradation of organic matter. In stage VI, the contents of LB-EPS and tightly bound EPS reach their highest levels at 21.47 and 30.74 mg/g-MLSS, respectively. Although CCW reduces microbial diversity, it increases the abundance of functional bacteria and the expression of genes related to organic matter degradation (such as Proteobacteria and Halobacterota). This study provides a theoretical basis and engineering insights for the anaerobic digestion treatment of CCW.