Design and Testing of an Optimized Anaerobic Digestion System

Abstract

This paper presents the design and testing of an optimized anaerobic digestion system by focussing on the thermal, mechanical and chemical aspects of the anaerobic digestion process parameters such as temperature, organic loading rates, air tightness and mixing. Eleven pilot batch biogas digesters were fabricated based on an already existing design and using locally available construction materials. Cow dung and poultry droppings were used as feed materials. The digesters were tested and ran for twelve months. Pressure buildup in the digesters started 24 hours after the initial loading, while combustible gas production was noticed after 72 hours. Tests results showed that the highest biogas yields were produced by poultry ratios 5, 6 and 7. A 7.1°C monthly average increase in temperature was observed during the period of study. The gas produced was found to be burning cleanly with a blue flame and no smoke. The optimum cow dung/ poultry droppings ratio for better anaerobic digestion performance was obtained and found to fall between 1.4 and 1.6 g VS/L under near thermophilic conditions. Complete digestion of the feed was accomplished within 14 days of hydraulic retention time. Improved biogas generation would greatly influence sustainable development, waste management and economic development in affected communities.