Enhancement of anaerobic co-digestion performance at the high organic load by application of waste seashell: the synergistic impacts of alkaline additive

This study aims to enhance the performance of a low-buffered anaerobic co-digestion of food waste and sewage sludge using an alkaline-based additive (waste seashell). Eighteen lab-scaled reactors were performed to evaluate the synergistic effects of waste seashell on methane production at different organic load. The addition of waste seashell showed significant synergistic effects with organic load on the anaerobic co-digestion performance in reducing the inhibitory level of volatile fatty acids and ammonia by (i) increasing buffer capacity of the systems, (ii) providing various slats, and (iii) changing the methanogenic pathway for achieving higher methane production yield. The addition of waste seashell with the concentration of 8 g/L, 20 g/L, and 26 g/L declined the propionic accumulation by 55%, 54%, and 49%, respectively, compared to their peer reactor at the same organic load. The utilization of waste seashell at 26 g/L increased the methane yield up to 219 mLCH 4 /gVS at an organic load of 15.6 gVS/L, represented 6.44, and 7.8-times higher methane yield and organic load increment, respectively, than that of conventional anaerobic co-digestion. However, at further increase of waste seashell and organic load, the anaerobic co-digestion showed low methane generation of 89.3 mL CH 4 /gVS due to the inhibitory impacts of calcium concentration on the biological process. Graphic abstract