A review: biogas production from tofu liquid waste

The tofu consumption will increase in the future. As consequent, the tofu production increases significantly. In other side, the amount of tofu wastes also increases. The solid waste can be utilized as solid compost but the liquid waste is discharged directly to the waster bodies at the moment. The latter is potential to be used as biogas feedstock. Some important factors affecting biogas rate need to be considered such as power Hydrogen (pH), Chemical Oxygen Demand (COD) to Nitrogen ratio, Total solid (TS) content, biological agent addition, initial concentration and two-stage anaerobic digestion. Furthermore, purification of the biogas formed by digestion of the tofu liquid waste is needed to be conducted to increase the methane content and decrease carbon dioxide (CO2) and hydrogensulfide (H2S) content. The H2S has to be removed prior to CO2 removal. The H2S can be removed by biofiltration and CO2 can be removed by biological absorption with help of microalgae. The effluent of anaerobic digester (digestate) may still contain high pollutant so it can be used as nutrient sources for microalgae. The zero waste system for tofu industries is successfully proposed in this paper. Future trend in treating tofu liquid waste in not only for biogas production butalso for biohydrogen production.