How does synthetic musks affect methane production from the anaerobic digestion of waste activated sludge?

The increasing use of synthetic musks has led to a large amount of synthetic musks retaining in waste activated sludge (WAS) via wastewater treatment, thereby entering anaerobic digester. However, the potential effects of synthetic musks on WAS anaerobic digestion remain unknown. Herein, this study selected the dominant galaxolide (HHCB) in WAS as the typical synthetic musks and experimentally evaluated the long-term effects on WAS anaerobic digestion using continuous lab-scale anaerobic digesters as well as the mechanisms involved. The results demonstrated that the increased HHCB levels (i.e., 90, 150 and 200 mg/kg-dw) resulted in the decreased methane production, with the methane production at 200 mg/kg-dw being only 80.5 ± 0.1% of the control. Supporting the methane production data, volatile solids (VS) destruction decreased by 18.6 ± 0.9%, which increased 6.8% of volume waste sludge for transfer and disposal. Correspondingly, the microbial community was shifted in the direction against anaerobic digestion. By modeling based on biochemical methane potential tests and investigating the key stages involved in anaerobic digestion, it was found that although the HHCB showed little impacts on the solubilization, WAS hydrolysis-acidification steps was inhibited by HHCB with the decreased hydrolysis rate and methane production potential, thereby causing the deteriorated performance of WAS anaerobic digestion.