Investigation of the Effect of Percentage Carbohydrate Composition on Carbon/Nitrogen Stability on Biogas Yield from Selected Kitchen Biodegradable Wastes

Abstract

This study investigated the effect of varying percentage carbohydrate composition on carbon/nitrogen (C/N) stability and subsequent biogas yield from selected kitchen biodegradable wastes. The objective was to optimize the anaerobic digestion process for maximum energy recovery by identifying the ideal C/N ratio. Experiments were conducted in 10 litres batch plastic digesters under mesophilic conditions range of 35-37 ⁰C, utilizing different mixtures of kitchen wastes to achieve specific C/N ratios (<30, >30, and 20≤C/N≤30). Feedstocks were characterized for their percentage composition of carbohydrates. The volume of daily biogas production and methane concentration were measured over a defined hydraulic retention time (HRT) of 45 days. Digester stability was monitored by tracking pH of the slurry throughout the HRT. The results obtained showed that biogas yield was significantly affected by the carbohydrate content and the C/N ratio, with the optimal range typically found with C/N ratio 20≤C/N≤30. The ratios outside this range resulted in lower yields due to nutrient imbalance or inhibition. The findings emphasize the critical importance of feedstock characterization and blending to achieve an optimal C/N ratio for efficient and stable biogas production from kitchen waste. This research provides valuable insights for waste management and renewable energy applications, highlighting a practical approach to maximizing energy potential from a readily available organic waste source. Keywords: Anaerobic digestion; Kitchen waste; Carbon–nitrogen ratio; Carbohydrate c