Understanding the mechanism of polybrominated diphenyl ethers reducing the anaerobic co-digestion efficiency of excess sludge and kitchen waste.

Polybrominated diphenyl ethers (PBDEs) widely existing in the environment can pose a serious threat to the ecological safety. However, the influence of PBDEs on methane production by excess sludge (ES) and kitchen waste (KW) anaerobic co-digestion and its mechanism is not clear. To fill this gap, in this work, the co-digestion characteristics of ES and KW exposed to different levels of PBDEs at medium temperature were investigated in sequencing batch reactor, and the related mechanisms were also revealed. The results showed that PBDEs reduced methane production and the proportion of methane in the biogas. Methane yield decreased from 215.3 mL/g· volatile suspended solids (VSS) to 161.5 mL/(g·VSS), accompanied by the increase of PBDE content from 0 to 8.0 mg/Kg. Volatile fatty acid (VFA) yield was also inhibited by PBDEs; especially when PBDEs were 8.0 mg/Kg, VFA production was only 215.6 mg/g VSS, accounting for 75.7% of that in the control. Mechanism investigation revealed PBDEs significantly inhibited the processes of hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Further study showed that PBDEs could inhibit the degradation and bioavailability of ES and KW, but it had a greater inhibition on the utilization of KW. Enzyme activity investigation revealed that all the key enzyme activities related to methane production were suppressed by PBDEs.