Abstract
Any type of biomass can be used as substrate for biogas production, but the performance of the biodigestion depends on the composition of the feed, and no direct extrapolation of the yield of the process from one substrate to another can be made. In this work, the performance of a bench-scale anaerobic biodigester of 93 L installed at ambient conditions is studied. The biodigester was set up in a region where temperature varies significantly during the year, and was operated under semi-batch conditions with non-thermal control for 16 months with a feed of rabbit manure and ground sorghum grains. To our knowledge, this is the first time the co-digestion of rabbit manure with sorghum grains is considered. To evaluate the biodigestion performance, critical operational variables (pH, temperature, biogas flowrate) were monitored, and composition of substrate, digestate and produced biogas was determined. Moreover, the following variables were quantified: (a) the theoretical methane potential, (b) the specific methane yield and (c) the degree of degradation of the substrate. A 1-D non-stationary model was formulated and validated with experimental data in order to analyze, in a theoretical form, the impact of incorporating thermal insulation to the unit. The results show that is it possible to produce biogas in a bench-scale biodigester, with a novel feed of rabbit manure and ground sorghum grains, in a region with significant temperature changes along the year. Moreover, it is shown that the 1-D model constitutes a useful tool for the design or improvement of biodigesters regarding the insulation system and the warming policies.
Highlights
Technologies around renewable resources are gaining more importance
The substrate was composed by rabbit manure, ground sorghum grains and water in the proportions previously mentioned
It is worth noting that, according to our determinations, the C/N ratio for rabbit manure alone is 14.5, which is less suitable for anaerobic processes and requires the addition of a carbon source
Summary
Technologies around renewable resources are gaining more importance. Biogas constitutes a product derived from renewable resources and is defined as secondary energy source, which means that it is a product generated through transformation of primary energy carriers into higher quality products by applying a fermentation process (Deublein and Steinhauser 2008). Anaerobic conversion of organic matter such as animal manure and crop residues into biogas provides a clean and renewable source of energy and a nutrient-rich digestate for Regarding the substrate, it should be mentioned that all types of biomass can be used as substrates for biogas production as long as they contain carbohydrates, proteins, fats, cellulose, and hemicelluloses as main components. Anaerobic digestion has mainly been associated with the treatment of animal manure and sewage sludge from aerobic wastewater treatment. It has been demonstrated that the anaerobic co-digestion of manure and various biomass substrates increases the biogas yield (Li et al 2013b) and offers a number of advantages for the treatment of manure and organic wastes, improvement of fertilizer properties of the digestate and reduction of greenhouse gas emissions from manure and organic wastes (HolmNielsen et al 2009)
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