Influence of Sludge Retention Time on the Performance and Stability of Mesophilic Anaerobic Co-digestion of Food Waste with Waste Activated Sludge

Abstract

Two parallel digestion systems of food waste (FW) and waste-activated sludge (WAS) were successfully initiated using a continuous stirred-tank reactor (CSTR), and the effect of different reduction extents of sludge retention time (SRT) on the co-digestion of FW and WAS was investigated. SRT Reduction extents longer than 8.3 d were not conducive to the stable operation of the co-digestion system when the organic load rate (OLR) was increased. The reduction extent of SRT should be reduced gradually from 5 d to 0.9 d to achieve high load and stable operation of the co-digestion of FW and WAS. After a long-term operation (approximately 282 d), the co-digestion reached stable operation at SRT of 9.1 d and OLR (calculated by COD) of (12.9±1.5) g·(L·d)-1. The corresponding methane production, methane yield (calculated by COD), pH, and volatile fatty acid (VFA, calculated by COD) were 3.94-4.25 L·(L·d)-1, 288-302 mL·g-1, 7.80-7.83, and 0.32-0.39 g·L-1, respectively. Additionly, the sludge characteristics of the co-digestion of FW and WAS under a high loading rate were also investigated. The results showed that the primary pathway of methane conversion was through acetic acid during the co-digestion of FW and WAS. Meanwhile, higher methanogenic activity of acetic acid, propionic acid, butyric acid, valeric acid, and coenzyme F420 concentration were also measured.