Biodegradation pathway of organophosphate esters in sludge composting implications for environmental safety

Organophosphate esters (OPEs) are emerging contaminants of growing concern, and there is limited information about the bacterial transformation during sludge composting. In this study, under the stress of 100 mg/kg ∑₇OPEs, three bacterial strains with degradation capabilities-Bacillus subtilis, Bacillus licheniformis, and Ralstonia pickettii-were screened and isolated, and a synthetic bacterial community (SynCom) was constructed. During 55 days sludge composting, the concentration of ∑₇OPEs decreased significantly. In CK, TnBP degraded the fastest (> 90%). For the exogenous OPE-added groups strengthened with SynCom (T1B and T2B), the removal rates of TCPP and TPhP were nearly complete (> 93%). However, high concentrations of ∑₇OPEs inhibited the degradation of compounds such as TCrP and EHDPP. Hydrolysis was identified as the preferentially initiated pathway for ∑₇OPEs degradation during sludge composting. Functional enzyme such as phosphatase, as well as bacterial strains from the Rhodococcus and Paracoccus, synergistically participated in the degradation process. Multiple linear regression analysis confirmed that SynCom promoted ∑₇OPEs removal by boosting phosphomonoesterase activity and enriching phosphatase-producing microorganisms. pH and total phosphorus (TP) emerged as critical environmental factors influencing this degradation. Composting significantly lowered OPE-associated ecological risks, ensuring the safe resource recovery of sludge. This study focused on the biological removal of OPEs during sludge composting. It first systematically evaluated the biodegradation efficiency of ∑₇OPEs and clarified core metabolic pathways. Furthermore, key microbial communities and functional genes associated with ∑₇OPEs degradation were identified, revealing their regulatory roles. It provides scientific support for controlling OPEs pollution and promoting sludge resource utilization.