Influence of Digester Height-to-Diameter Ratio on Biomethanation of Market Vegetable Wastes

Abstract

Biogas digesters are used to produce methane gas from organic wastes such as vegetable wastes. They come in different sizes and designs depending on available space, costs, type of operations and other considerations. Fifteen types of vegetable wastes from Cagayan de Oro markets were anaerobically digested in a batch-type digester with cow manure as inoculum at ambient conditions for 40 days. Five 1-L plastic cylinders with different height-to-diameter ratios (0.77, 1.08, 1.58, 1.93 and 2.80) were used as digesters to determine the effect of digester height-to-diameter ratio on methane production using these vegetable wastes. Results revealed that the digester with the lowest height-to-diameter ratio produced the most methane (53.3%) after the retention time. In contrast, the digester with the highest height-to-diameter ratio yielded the least methane concentration (46.8%). This indicated that there was an inverse relationship between the ratio and the methane production of vegetable wastes mixed with cow manure. Although the results suggested a minor influence, the statistical analysis presented an insignificant influence of the height-to-diameter ratio on the biomethanation of vegetable wastes.