Enhancing methane production in anaerobic co-digestion of food wastes and sewage sludge: roles of different types of iron amendments

Iron element is known to be an effective additive for accelerating the anaerobic digestion (AD) process for treating organic wastes. However, the effects of different kinds of iron additives on food waste (FW) and sewage sludge of co-digestion process have not been yet investigated thoroughly. This study aimed to elucidate how different kinds of iron components affect methane production during FW and sewage sludge anaerobic co-digestion (co-AD) process and to investigate the possible mechanism of Fe amendment. Experimental results revealed that Fe amendment could effectively promote the substrate degradation and methane production, and FeCl₃ amended group presented the best digestion performance, boosting the methane production from 465.9 mL to 2650.4 mL. The results of the excitation-emission matrix fluorescence spectra analysis further supported that Fe supplements facilitated the waste hydrolysis with a higher concentration of dissolved organic matters and thereby more substrates can be used for methane generation. In addition, the activity of coenzyme F420 and direct interspecies electron transfer in FeCl₃ group were 5.82 and 5.89 times higher than those in the control group, respectively, indicating that electron transfer, particularly the interspecies one, was enhanced by Fe amendment. As compared to that in the control group, the increased cytochrome c concentration in Fe amended groups also proved it. Therefore, this study will provide a reference regarding Fe amendment in the co-AD process for FW and sewage sludge.