Anaerobic manure treatment under extreme temperature conditions

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Usually anaerobic treatment of manure is performed as one stage fermentation under mesophilic (30-35°C) or moderate thermophilic (50-55°C) conditions, with the aim to stabilize organic material for the use of digested manure as a fertilizer. The present study was conducted to develop a new approach for manure treatment, which concerned the sanitation of manure and saving energy for its treatment. Laboratory scale experiments were performed on the digestion of cattle and pig manure under psychrophilic conditions (5-20°C) and extreme thermophilic (55-82°C) conditions. Specifically, we were interested in the digestive activities of microbial populations under low and high temperature conditions. Long-term adaptation (or selection) of active psychrophilic microbial communities is essential to perform sufficient manure treatment at low temperatures. Results of this investigation indicated the development and accumulation of a specific microbial populations at high and at low temperatures in both cattle and pig manure. An acclimated methanogenic microbial community active at 5°C was obtained after 1.5-years incubation of cattle manure at low temperatures, prior to digestion under mesophilic conditions. Fermentation under high temperature conditions resulted in the development of a thermophilic acidogenic microbial populations, with the observed accumulation of volatile fatty acids in the liquid fraction of manure. Thus, a two-step anaerobic manure treatment is proposed in which the sanitation of manure and saving energy present: i) acidogenic fermentation at high temperature, ii) separation for solid and liquid fractions, iii) treatment of liquid manure fraction under low temperature conditions.