Abstract
Biogas plants are the most complex systems and are heavily studied in the field of renewable energy. A biogas system is mainly influenced by biological and technical parameters that strongly interact with each other. One recommended practice when operating a biogas plant is the recirculation of the substrate from the second fermenter into the first fermenter, which extends the recirculation amount (RA) and, in turn, the recirculation rate (RR). This technique should be applied to support and secure the biogas process. In this investigation, the RA was varied, starting with the recommended “best practice” of 10.0 m3/d (RR 40%). Every ten days, the RA was reduced in steps of 1.5 m3/d, with 5.5 m3/d (RR 27%) being the final value. The basic question to be addressed concerns to what extent the RR influences the methane yield and thereby influence the efficiency of a manure-based biogas plant in practice. Diverting the “best practice” to a RR of 27% stabilised the fermentation process and lead to significantly higher methane yields with smaller standard deviations. In addition, with a reduced RR, the standard optimal acid concentration within the biogas substrate was approximately reached.
Highlights
In today’s society and economy, there is high acceptance of biogas as a green energy resource because of increasingly energy-demanding lifestyles [1] and dwindling fossil resources
The calculated organic loading rate (OLR) and hydraulic retention time (HRT) confirm these values to be the most important parameters describing the functionality of the biogas system with regard to the economic viability of the optimized substrate reduction
We demonstrated that an increasing recirculation rate (RR) results in lower concentrations of various organic acids (Figure 7) and leads to a positive effect on the acid concentration as well as of various organic acids (Figure 7) and leads to a positive effect on the acid concentration as well as in in the pH-regulation
Summary
In today’s society and economy, there is high acceptance of biogas as a green energy resource because of increasingly energy-demanding lifestyles [1] and dwindling fossil resources. The use of biogas as a renewable energy source based on energy crops and organic residual materials is of high importance [2], even in the agricultural sector. Biogas technology has been refined through many studies over the last few years. Two main key levers of biogas research can be distinguished: the understanding of microbiological activity and function and the optimization of the engineering performance. The type of supply and the fermentation temperature are two of the main technical aspects of concern in a biogas plant. Most biogas plants are mainly fed with energy crops and a small amount of manure
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