Performance and Microbial Analysis of Anaerobic Digesters Treating Food Waste and Dairy Manure

摘要

The stability and microbial population of completely mixed anaerobic digesters were evaluated during the treatment of manure, food waste, and their mixtures at a temperature of 35�C � 2�C and a hydraulic retention time of 20 days. Two mixtures were tested; the first mixture composed of 32% and 68% and the second of 48% and 52% food waste and dairy manure, respectively, based on volatile solids (VS). The digesters treating manure and the two mixtures showed stable performance at an organic loading rate (OLR) of 4 g VS L-1 day-1. However, the digester treating food waste was not stable at this OLR nor at the reduced OLR of 2 g VS L-1 day-1, as indicated by high volatile fatty acid concentrations and low pH in the digester and low biogas producion rate. The results of this study show that the co-digestion of food waste and dairy manure significantly increases the biogas production rate as compared to digestion of dairy manure alone. The measured biogas production rates were 1.26, 1.91, and 2.02 L L-1 day-1 for manure, first mixture, and second mixture, respectively, at OLR of 4 g VS L-1 day-1. Thus, the addition of food waste into dairy digesters is a feasible method for improving the economics of dairy farm digesters. Microbial analysis of the digester contents revealed that the food waste digester contained statistically greater numbers of clones related to the phyla Thermotogae and Actinobacteria, and the manure digester contained greater amounts of the phyla Firmicutes, Bacteriodetes, and Spirochetes. The archaeal population structure had little difference in the digesters fed with different substrates and was composed of hydrogenotrophic, acetotrophyic, and methylotrophic methanogens.