Comparison of Biogas Productivity in Thermophilic and Mesophilic Anaerobic Digestion of Bioethanol Liquid Waste

Most of the anaerobic digesters in Indonesia are run under mesophilic conditions because the Indonesian climate is sufficiently pleasant to maintain mesophilic conditions easily. On the other hand, thermophilic anaerobic digestion offers an advantage of a much higher biogas production rate, although it needs more tedious control and energy supply to achieve the thermophilic temperature of 50-60°C. We run laboratory-scale experiments to compare the process performance of anaerobic digestion of bioethanol liquid waste (vinasse) at mesophilic and thermophilic conditions. Inoculum on this test using digested cow manure. Start-up was conducted with only the inoculum inside the reactors. After the reactor passed through the starvation period, the vinasse feeding was started. The hydraulic retention time (HRT) was gradually decreasing from 60, 42, until 30 days. Each step of HRT took 7 up to 14 days for stabilization. At the same HRT, thermophilic reactors produced biogas at the rate of four times faster than the mesophilic reactors. The methane concentration in the biogas for the thermophilic process was relatively the same as the mesophilic one. With such a higher rate of biogas production, the energy cost for thermophilic can be possibly better compensated.