Synergistic enhancement of real coal chemical wastewater treatment by aerobic granular sludge, iron-carbon microelectrolysis, and co-substrate regulation.

Coal chemical wastewater (CCW) can destabilize sludge structure and cause performance fluctuations in biological systems. Aerobic granular sludge (AGS) is structurally compact and resistant to shock loading. In this study, AGS was integrated with iron-carbon microelectrolysis (IC-ME) conditioning and co-substrate regulation for CCW treatment. Together, these strategies alleviated toxic stress and substrate limitation, stabilized the granular microenvironment, and promoted pollutant biotransformation. Two sequencing batch reactors were operated in stages to compare AGS alone with co-substrate addition, IC-ME conditioning, or both. Removal efficiencies for chemical oxygen demand, total organic carbon, and total nitrogen reached 83.1%, 76.5%, and 66.9%, respectively, in the synergistic system. Phenols, polycyclic aromatic hydrocarbons, benzene, toluene, ethylbenzene, xylenes, and nitrogen-containing heterocyclic compounds showed stage-dependent removal. After IC-ME introduction, MLSS and SVI30 reached 1.5 g/L and 43.4 mL/g, respectively; under high loading, ammonium nitrogen removal recovered to 83.1%. Protein content in loosely bound extracellular polymeric substances increased, while dehydrogenase activity reached 8.68 μg TF/(mL·h), reflecting oxidative metabolism. Catechol 1,2- and 2,3-dioxygenase activities reached 0.0050 and 0.0076 U/mg Pro, respectively, supporting aromatic ring cleavage. Community analysis identified Flavobacterium and Thauera as dominant genera, while principal component analysis linked restructuring to stage, co-substrate addition, and IC-ME conditioning. Deterministic contributions to community assembly increased, while napA and napB enrichment indicated denitrification potential. Mechanistically, IC-ME conditioning and co-substrate-supported metabolism jointly supported organic transformation and nitrogen conversion across the staged operation. This study offers mechanistic and operational guidance for AGS treatment of real CCW.