Two-stage anaerobic digestion of food waste and horticultural waste in high-solid system

A two-stage process was proposed to increase biogas yield, efficiency and stability of the codigestion process of food waste, chicken manure and horticultural waste in a high-solid system. In this two-stage process, high-solid codigestion of food waste and chicken manure was carried out in the first stage and then, transferred and codigested with grass in the second stage. It was found that high-solid digestion of food waste failed after 3 days because of the accumulation of volatile fatty acids (VFAs). The two-stage process could be optimized by adjusting the mass ratio (based on volatile solids (VS)) among food waste, chicken manure, and grass, and a ratio of 4:5:5 of food waste to chicken manure to grass could lead to the highest biogas yield and efficiency. The biogas yield of the two-stage process 83.25% higher and the duration of digestion was 18 days shorter than those of the codigestion. The VS removal efficiency of the two-stage process was 57.30% higher than that of one-stage codigestion. When the organic loading rate (OLR) was 4.00 gVS/(L·day), the two-stage process was stable, with an average methane yield of 113.4 mL/gVS.