Use of a Portable Greenhouse for Temperature Control in a Small-scale Biogas Production Unit

Abstract

Biogas yield in anaerobic digesters is negatively affected by low temperatures during cold seasons and nights, temperature fluctuations and inefficient agitation. In this study a 100 ℓ, agitated portable carbon steel digester housed within a greenhouse, whose operation temperature is automatically maintained at 35±1^oC by means of an electronic circuit for ventilation control through a suitably sized window and insulation offered by an air film between a double layer of polyethylene plastic covering of the greenhouse, was designed. Analysis of biogas produced from cow dung starting from day 6 of the 31-day retention period showed a specific biogas yield of 0.036 m3/kgVSadded and an improved methane yield of 55% which was higher than 50% achieved by other digester designs. The optimum pH for good buffering capacity and efficient anaerobic digestion was successfully maintained at 7.2 and the COD reduction achieved was 61%. The maintenance of a narrow temperature range (34℃-36℃) was successful resulting in solving the challenge of poor temperature control which affects biogas production and methane yield in most small-scale digester designs. This simple, easy to construct, inexpensive and efficient design led to improved biogas yields, quality and faster dissemination of biogas technology.