Abstract
In this work, performance and microbial structure of a digestion (food waste-only) and a co-digestion process (mixture of cow manure and food waste) were studied at mesophilic (37 °C) and thermophilic (55 °C) temperatures. The highest methane yield (480 mL/g VS) was observed in the mesophilic digester (MDi) fed with food waste alone. The mesophilic co-digestion of food waste and manure (McoDi) yielded 26% more methane than the sum of individual digestions of manure and food waste. The main volatile fatty acid (VFA) in the mesophilic systems was acetate, averaging 93 and 172 mg/L for McoDi and MDi, respectively. Acetate (2150 mg/L) and propionate (833 mg/L) were the main VFAs in the thermophilic digester (TDi), while propionate (163 mg/L) was the major VFA in the thermophilic co-digester (TcoDi). The dominant bacteria in MDi was Chloroflexi (54%), while Firmicutes was dominant in McoDi (60%). For the mesophilic reactors, the dominant archaea was Methanosaeta in MDi, while Methanobacterium and Methanosaeta had similar abundance in McoDi. In the thermophilic systems, the dominant bacteria were Thermotogae, Firmicutes and Synergistetes in both digesters, however, the relative abundance of these phyla were different. For archaea, the genus Methanothermobacter were entirely dominant in both TDi and TcoDi.
Highlights
Anaerobic digestion process has widely been employed for treatment of various organic wastes because the process can be used for production of value-added products such as an energy-rich gas and bio-fertilizer
While the pH of thermophilic digester (TDi) was similar to mesophilic processes, an elevated pH was clearly seen for thermophilic co-digester (TcoDi)
This agrees with the higher ammonia concentrations in the co-digestion systems (McoDi and TcoDi), which were 16.5% and 13.7% higher than the mesophilic digester (MDi) and TDi digesters, respectively (Fig. 2)
Summary
Anaerobic digestion process has widely been employed for treatment of various organic wastes because the process can be used for production of value-added products such as an energy-rich gas and bio-fertilizer. This process is carried out by a complex microbial community which degrade various organic compounds into final products such as methane and carbon dioxide, collectively called biogas. The aim of this study was to investigate the microbial structure of co-digestion of food waste and cow manure under mesophilic (37 °C) and thermophilic (55 °C) conditions. Performance parameters were studied under the various conditions and it was attempted to explain performance efficiencies using microbial data
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