Abstract
In this study, productivity and physicochemical and microbiological (454 sequencing) parameters, as well as environmental criteria, were investigated in anaerobic reactors to contribute to the ongoing debate about the optimal temperature range for treating animal manure, and expand the general knowledge on the relation between microbiological and physicochemical process indicators. For this purpose, two reactor sizes were used (10 m3 and 16 l), in which two temperature conditions (35°C and 50°C) were tested. In addition, the effect of the hydraulic retention time was evaluated (16 versus 20 days).Thermophilic anaerobic digestion showed higher organic matter degradation (especially fiber), higher pH and higher methane (CH4) yield, as well as better percentage of ultimate CH4 yield retrieved and lower residual CH4 emission, when compared with mesophilic conditions. In addition, lower microbial diversity was found in the thermophilic reactors, especially for Bacteria, where a clear intensification towards Clostridia class members was evident.Independent of temperature, some similarities were found in digestates when comparing with animal manure, including low volatile fatty acids concentrations and a high fraction of Euryarchaeota in the total microbial community, in which members of Methanosarcinales dominated for both temperature conditions; these indicators could be considered a sign of process stability.
Highlights
Anaerobic digestion of organic by-products is a key technology for producing high-value bioenergy in form of biogas
Anaerobic digestion reduced total solids (TS) and volatile solids (VS) in the manure compared with non-digested cattle manure in all experiments
Anaerobic digestion process considerably decreased the concentration of total volatile fatty acids (VFA) in the samples, and changed the composition of the detected VFA pool, when comparing with the initial VFA content (Table 2)
Summary
Anaerobic digestion of organic by-products is a key technology for producing high-value bioenergy in form of biogas. Temperature and substrate composition are among the main factors affecting performance and stability of anaerobic digestion process (Ziganshin et al, 2013; Labatut et al, 2014). No consensus exists on the temperature range that optimizes the treatment for each substrate, since different criteria can be considered. This is a special challenge when animal manure is used, because the bioenergy production, and environmental and operational aspects must be considered. Mesophilic conditions are still recommended for treating animal manure (Labatut et al, 2014) based on a higher robustness of the process
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