Design and Fabrication of Electric Jacketed Anaerobic Digester

Abstract

An anaerobic bio-digester is a bioreactor used to convert organic matter to biogas through anaerobic reaction carried out by a consortium of micro-organisms. The activities of the micro-organisms and biogas yield depend on digester operating factors which include temperature, pH, agitation, total solid content, organic loading rate and concentration of substrate. Unfortunately, lack of introducing monitoring and proper control of the temperature, pH and agitation result into large hydraulic retention time and low biogas generation which consequently limits the popularization of biogas technology in rural areas. This problem can be solved by designing and fabricating an anaerobic digester which incorporates proper monitoring and control of these factors in order to achieve maximum yield of biogas and reduced retention time. Hence, a jacketed bio-digester system which incorporates a heater, an agitator and a pH probe was designed, fabricated and successfully utilized for the anaerobic co-digestion of kitchen waste and cow dung. The digester was operated at a constant volume of 12 kg, temperature of 40 oC, agitation speed of 30 rpm, a total solid content of 8% and pH of 7.5 for a period of 70 days. The pH, agitation and temperature of the substrate were introduced, monitored and controlled in the reaction. The biogas yield showed a good performance of the bio-digester system. This bio-digester system can be used for laboratory experiments to train students on the conversion of biodegradable solids to biogas. It can also be used to simulate a biogas plant and generate energy for laboratory use.