How does food waste to municipal sludge ratio affect anaerobic digestion: performance evaluation and fate of antibiotic resistance genes.

Anaerobic co-digestion of food waste (FW) and sewage sludge (SS) has shown superior performance over anaerobic mono-digestion. However, the fate of antibiotic resistance genes (ARGs) under various co-digestion ratios has been rarely reported to date. Thus, this study investigates the effects of FW:SS ratios on the digester's performance and the fate of ARGs at different FW:SS ratios. The results demonstrated that at a 50:50 FW:SS ratio, 738 mL.g VS of biogas and 393 mL.g VS of methane were produced in the system on day 18. Response surface methodology (RSM) was also used for optimization, showing 42.5% FW is the optimal FW content for maximum biogas and minimum HS production. The distribution of select ARGs (qnrS, tetA, emrB, bla, ampR) was tracked in the liquid and solid fraction of the digestate. Results illustrated a decrease (83-99% reduction) in the overall abundance of the ARGs in the solid fraction after AD. A similar trend was observed for the ARGs in the liquid fractions (65-99% reduction), except for ermB which became 1.74-10.6-fold higher in the final digestate. Also, at 50% FW, the abundance of intl1 increased in the liquid and solid fraction of digestate, indicating increased potential of ARG dissemination via horizontal gene transfer.