Abstract
Anaerobic co-digestion of sheep manure and potato waste was studied under batch and semi-continuous conditions. Biochemical methane potential tests were carried out for the different substrates before evaluating co-digestion at high-solid content. The reactors presented stable performance under mesophilic conditions, at an organic loading rate (OLR) of 3.5–4.0 kg VS/m3 and a hydraulic retention time (HRT) of approximately 20 days. Increasing the OLR of semi-continuous reactors decreased the methane yield and degradation efficiency of the digestion. Methane-specific production was in the range of 196 and 467 mL CH4/g vs. (sheep manure system and co-digestion, respectively). Based on the experimental data obtained, a techno-economic study was performed for wet and solid-state fermentation systems, with the first configuration presenting better results. The economic feasibility of the hypothetical plant was analyzed considering the variability in electricity and compost selling prices. The economic feasibility of the plant was determined with an electricity selling price of EUR 0.25/kWh, and assuming a centralized plant serving several farmers. Still, this price was considered excessive, given the current electricity market values.
Highlights
Anaerobic digestion is a well-established process for the treatment of organic wastes and the recovery of energy through biogas valorization
This material is suitable for operating under a high solid content configuration, given the high value of volatiles
Sheep manure presented behavior that can be categorized as linear in its initial stage, which is indicative of hydrolysis limitations
Summary
Anaerobic digestion is a well-established process for the treatment of organic wastes and the recovery of energy through biogas valorization. The process transforms organic compounds into methane-rich gas, which is transformed into electricity, helping to mitigate global warming [1]. A liquid slurry is obtained from the digestion process, called digestate, which contains microbial biomass, metabolic compounds, complex organic structures, and material that is not degradable under anaerobic conditions. The benefits of anaerobic digestion are clear, but the economic feasibility of this type of treatment plant are not as clear. Digestion technology should be considered an important adjunct to aid in the prevention of environmental pollution, and the production of renewable energy. The reality is that the number of digestion plants treating manure in Spain is much lower than in other European countries, due to inadequate public incentives
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