Bio-promoter-driven conversion of 4-chlorophenol into utilizable carbon source: Enhancing electron supply-consume and attenuating bio-toxicity.

4-chlorophenol (4-CP), a toxic organic compound, poses dual challenges in biological wastewater treatment: disrupting denitrification and remaining underutilized as potential carbon sources. Transforming 4-CP into a utilizable carbon source not only mitigates its inhibitory effects on denitrification but also supports microbial metabolism for enhanced nitrogen removal. This study presents a composite bio-promoter integrating a basic bio-promoter (growth factor and antidote) with phosphomolybdic acid (PMo) to convert 4-CP into utilizable carbon source by enhancing electron supply-consume and attenuating bio-toxicity. 60 mg/L 4-CP inhibited nitrogen removal by decreasing 29.12% of nitrate reductase (NAR) and 27.53% of nitrite reductase (NIR) activities. Meanwhile, 4-CP impaired electron supply by reducing 54.80% of glucose-provided chemical oxygen demand through inducing severe lipid peroxidation. Composite bio-promoter recovered nitrogen removal to 96.43% within 33T, a 53.20% improvement over self-recovery. Basic bio-promoter increased biomass by 1.63-fold, and its synergy with PMo facilitated oxidative-antioxidant homeostasis, enhancing electron supply and alleviating cellular damage. Molybdenum-mediated electron shuttling shortened transfer distances and increased flavin adenine dinucleotide levels by 9.27 pg/mL. Functional genes linked to NO-N and NO-N reduction (napA, napB, napC, narG/nxrA, narH/nxrB, narI, and nirS) were significantly up-regulated, supporting enhanced denitrification-linked electron consumption. The bacteria that simultaneously possessed 4-CP-glucose metabolism and denitrification functions cooperated, particularly Acidovorax and unclassfied_c_Betaproteobacteria, further enabled the conversion of 4-CP into utilizable carbon sources.