Effects of substrate organic composition on mesophilic and thermophilic anaerobic co-digestion of food waste and paper waste

Abstract

Facing the huge output of food waste (FW) and paper waste (PW), long-term semi-continuous experiments were carried out to investigate the effect of the substrate organic composition on mesophilic and thermophilic anaerobic co-digestions (Co-ADs) of their mixtures. The experimental results showed that the organic composition of the substrate affected the biogas and methane production and yield of the two Co-ADs of the FW and PW mixtures, and its effect on thermophilic Co-AD (Co-TAD) was lower than that on mesophilic Co-AD (Co-MAD). The two Co-ADs had similar biogas (2.158 ± 0.136 L/L/d and 2.183 ± 0.142 L/L/d) and methane production (1.245 ± 0.082 L/L/d and 1.279 ± 0.088 L/L/d), and organic matter degradation (81.79 ± 1.07% and 83.81 ± 1.09%) when the substrate organic composition was carbohydrates:proteins:lipids = 6.8:1.8:1 (low carbohydrate composition, FW:PW = 4:1). When the substrate organic composition was carbohydrates:proteins:lipids = 13.5:2:1 (high carbohydrate composition, FW:PW = 1:1), the thermophilic temperature was more favorable than the mesophilic temperature for the Co-AD of FW and PW mixtures. The characteristics (pH, total ammonia, total volatile fatty acids, and total alkalinity) of the Co-TAD digestate were more sensitive to changes in the organic composition of the substrate than those of the Co-MAD digestate. Increasing the carbohydrate content of the FW:PW mixture lowered the production of biogas and methane, and degradation of organic matter in both Co-ADs.