Physicochemical Characterization and Biogas Potential Assessment of Three Organic Substrates

Abstract

This study evaluates the biogas and methane production potential of three organic substrates, namely slaughterhouse waste, camel dung, and brewery waste (brewers’ spent grain), to assess their suitability for anaerobic digestion and renewable energy production. The evaluation was based on the physicochemical characterization of the substrates, including organic matter content and carbon-to-nitrogen (C/N) ratio, which are recognized as key factors influencing microbial activity, process stability, and methane generation. Fresh samples were analyzed using standardized laboratory methods to estimate theoretical biogas potential together with expected biogas and methane yields. Results show that physicochemical composition strongly affects methanogenic performance. Camel dung exhibited high organic matter content and a favorable C/N ratio (20.2), resulting in a methane yield of 111 Nm³ CH₄/t FM and good process stability. Its balanced nutrient composition provides favorable conditions for methanogenic microorganisms, promoting efficient organic matter degradation and stable methane production. These characteristics identify camel dung as the most suitable substrate for anaerobic digestion among those investigated. In contrast, brewery waste showed the highest theoretical biogas potential (650 LN/kg OM) due to its high biodegradable organic matter content. However, its low C/N ratio (5.4) increased the risk of ammonia inhibition, limiting methane yield to 75 Nm³ CH₄/t FM despite its considerable energy potential. This finding demonstrates that a high theoretical biogas potential does not necessarily result in high methane production when nutrient balance is unfavorable for microbial metabolism. Although slaughterhouse waste had an optimal C/N ratio (23.3), it produced the lowest methane yield (32 Nm³ CH₄/t FM), suggesting lower biodegradability. This reduced performance may be associated with the presence of protein- and lipid-rich compounds capable of generating inhibitory intermediates that negatively affect methanogenic activity and methane conversion efficiency. Overall, camel dung appeared to be the most balanced substrate, while spent grain represents a promising energy-rich co-substrate and slaughterhouse waste a complementary feedstock for co-digestion. Their complementary characteristics suggest that co-digestion could optimize the C/N ratio, improve process stability, and enhance methane production. Analyses were conducted at the Biogaz PlanET France laboratory.