Biomethanation of tofu liquid waste using two-stage anaerobic fermentation system

Biogas is a renewable energy source that is undergoing continual improvement in its technique and method of fermentation. The use of biogas in small industries or households is still facing un-fully utilized waste material, although it has a large potential to produce biogas. One of these underutilized waste materials comes from the tofu making industry, a common household industry in Indonesia, especially in Bandung. Generally,household-scale biogas productionuses a single bio-digester (one stage anaerobic fermentation) technology, which accommodates two main principles of biogas formation, namely the acetogenic stage and the methanogenic stage. The problems that arise from the use of a one-stage biogas digester are the imbalance of the fermentation process due to differences in environmental conditions at each stage, increasing of the organic load rate, the longer retention time of the organic compound, and low biogas productivity. Those issues result in un-optimized production. From this condition, a study of the application of biogas production through a two-stage anaerobic digestion fermentation system through fed-batch fermentation was conducted. We found that the decrease of the chemical oxygen demand (COD) value of tofu waste reached 21%-38% in acetogenic fermentation and 71% in the methanogenic digester. Biogas production yielded the highest methane gas composition value at 74.05%, and the highest biogas volume of 48.55 L/day, with highest energy potential value at 1249,2 kJ/day.