BLOG ENTRY #3: Biogas Digester

24 Mar

Biogas digester suited in rural areas

The increasing number of swine farms in the Philippines creates problems on waste disposal affecting human health and environment. Biogas digesters help lessen these problems, but technical constraints and high cost of investment prevent the use of biogas digesters in rural areas.

To address these problems, researchers of the Department of Agriculture-Western Mindanao Integrated Agricultural Research Center led by Andrew M. Balili evaluated three types of biogas digesters to determine the design suited to the villages. These are the fixed type design that uses plastic drum as tank for anaerobic digestion; the floating dome type with digester made of 4 ft x 4 ft rectangular concrete and with a floating gasholder made of plain GI sheet; and the commercial type, a cylindrical floating dome type 8 ft diameter digester.

The digesters were evaluated based on gas production; duration of gas supply to stove which was operated at various levels; time needed to refill the gas reservoir; sludge matter; and production cost.

Results showed that the commercial type digester has the highest gas production (1.78 m3) in 12 hours operation than the floating (0.71 m3) and fixed dome types (0.09 m3). Also, gas production from the commercial type was the longest to be consumed under low, medium, and high volume burning.

Based on laboratory analysis of sludge matter, biogas contains 1.09% nitrogen, 10.13% phosphoric acid, 1.44% potassium, and 9.28% moisture content (oven dry).

Also, findings show that biogasification or the microbial conversion of organic matter in anaerobic condition offers a systematic approach to manure treatment that does not only stabilize the wastewater but also produces a significant amount of energy in the form of biogas. It also controls odor, minimizes environmental impact from waste emissions, and maximizes fertilizer nutrient and water recovery for reuse.

Furthermore, the choice of digester to use at a given swine production operation depends on existing or planned manure handling. Researchers observed that the larger the reservoir, the greater the supply of gas generated. But having a large amount of waste stored in the digester does not ensure greater amount of gas production. Waste matters must also be stirred regularly to allow faster anaerobic decomposition.

In this study, the commercial type of biogas was effective in meeting the needs of 3-4 households subject to a more detailed economic evaluation. However, for a family of four, the floating type design is recommended.

The Western Mindanao Agriculture, Forestry and Resources Research and Development Consortium endorsed this study to PCARRD in 2006 as their entry to the National Symposium on Agriculture, Forestry and Natural Resources Research and Development then. PCARRD, on the other hand, featured this study in its publication “Highlights 2006” in response to the need of swine raisers and other concerned stakeholders.

-marc domingo


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