Simultaneous synergistic effects of addition of agro-based adsorbent on anaerobic co-digestion of food waste and sewage sludge

The aim of this study was to evaluate the performance of anaerobic co-digestion of food waste (FW) and sewage sludge (SS) at high organic load with the aid of an inorganic adsorbent supplementary. From BMP tests of seven mesophilic reactors, it was found that the stability of the system was hindered at higher organic load due to low alkalinity capacity of sludge (1600 mg/L) and excessive accumulation of inhibitory substances such as free ammonia and VFA. Thus, the low-cost adsorbent was applied to enhance the digestion process stability at high organic load (12.8 g VS/L). The results showed that addition of 1 g of sorghum-based activated carbon (SAC) (4 g TS/L) stabilized the system, reduced ammonia and T-VFA concentration from 267 to 39 mg/L, and 1300 to under 600 mg/L, respectively. Consequently, the methane yield increased from 201 to 272 mL/g VS (35%), solid retention time (SRT) reduced by 34%, and T-COD removal achieved by 79.38%. However, with a further increase of SAC the biogas generation decreased due to excessive adsorption of VFAs. Graphic abstract