An on-site survey on household-scale anaerobic digestion in Sri Lanka

In this study, household-scale anaerobic digestion (AD) in Sri Lanka was surveyed by visiting 100 AD users. The process flow, material flow, management of biogas and bioslurry, changes in waste disposal, and cost of construction were analyzed in terms of encountered problems. The main motivations to use AD are energy recovery by biogas and proper organic waste management instead of open dumping. On the other hand, several problems are clarified. The AD is mostly uneconomically oversized for the amount of input waste. Maintenance is poor, especially the lack of desulfurizer will reduce the lifetime of gas utilization equipment. The imbalance between supply and demand of biogas is also a problem. The example of low supply includes a case when only a limited part of livestock waste is only fed into AD, and it is necessary to supply accessories for lightning or electricity generation to users. To overcome these problems, technical guidance and assistance by national and local government are necessary. The possible scenario for extending the appropriate use of AD in the future for waste management shows with savings by maximized use of biogas and slurry, the implementation cost of the AD can be recovered mostly within a 6-year period.