Development and implementation of small-scale biogas balloon biodigester in Bali, Indonesia

Abstract: Indonesia, due to its abundant resource of organic waste and a climate characterized by elevated and constant temperatures, is perfectly suited for anaerobic degradation and biogas production without applying expensive technologies. A huge number of household-level fixed-dome biodigesters installed in the last years in Indonesia have manifested problems such as costs, complex logistics, a bad follow-up strategy, the poor quality of the material and lack of farmers’ knowledge to operate and maintain the system. For this reason, a local company started to develop a prototype of a household balloon biodigester technology as an alternative to the common system, as a solution for the identified problems. Starting from a deep understanding of the issues shown by the prototype pilot test, a literature review of the anaerobic degradation process and similar technologies applied in developing countries was conducted, and the balloon biodigester was improved and a final product implemented. A second pilot test was carried out to assess the technical and economic feasibility of the technology. Its results showed that, compared with the prototype, the developed balloon design led to an increased time to carry out the installation steps due to the excavation process, but a reduced time to complete the operational activities and higher stability of the balloon. Moreover, the system provided almost the same output as the fixed-dome digester, achieving biogas to cook for almost three hours per day with no weight system required to achieve a sufficient pressure to cook. The biogas production was considerably faster than the first prototype, due to the sunlight irradiation. The material used for the bag, PVC 550, appeared sturdy and elastic, therefore offering an effective solution for the balloon digester technology. However, the technology should be tested for a longer period of time to ensure that no problem occurs in the material and in the anaerobic degradation process. Additionally, the economic assessment showed that, with a final cost of 637 dollars, the developed technology is not advantageous for the farmers as a substitute for LPG for cooking and more expensive than a fixed-dome digester. This is due to the expenses that cover the installation and the cost of the material. However, if part of the biogas could be used to cover the electricity needs for lightning, the NPV could slightly increase. The sensitivity analysis showed that at least the investment cost should be reduced by 20% to 500 dollars or the LPG price would need to increase by 80%, reaching 0.86 dollars per kg to make the system profitable for the farmers.