Journal of the Society of Agricultural Structures, Japan

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Vegetable wastes accounts high percentage of plant residues in food industry wastes, and they are expected to be converted to biogas due to its high water content and large amount of waste. Since vegetable wastes have a low VS concentration, it is assumed that it will be used as a base raw material in anaerobic digestion, and additional materials are required to increase the amount of biogas production. In this study, we investigated the possibility of vegetable wastes as a base raw material by co-digestion of food biomass. A biogas potential test was conducted using five types of vegetable and boiled pasta as the main substrates, and cheese and chocolate as co-substrates. When 60 % of cheese or chocolate was added to the organic load of vegetable wastes, the amount of biogas production increased from 3.37 m³/m³ to 4.76 m³/m³ and 5.89 m³/m³ , respectively. The biogas yield also improved slightly. The effect of the mixing ratio of vegetable wastes and chocolate was investigated under the condition of constant organic load. Mixing 20-50 % of chocolate compared to mono-digestion of vegetables waste increased biogas production and biogas yield. From these results, it was shown that vegetable wastes and cheese and chocolate can be anaerobically co-digested, and that vegetable wastes can be used as a base substrate for co-digestion of food biomass.

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The mass and bulk density of supplementary materials for livestock manure composting in the pile state were estimated from the amount of subsidence in the small volume load test. Estimating the mass when piled up 2 meters high, it was about 60 % of the previous value for sawdust, and for rice husks it was about 80 %. Although the moisture content of returned swine manure compost was different, its mass was about twice the previous value. The value obtained with returned dairy manure compost was less than 40 % that of returned swine manure compost. It was estimated that the bulk density value increased as the deposition height increased even for the same material. This change was the smallest in rice husks, larger in sawdust and returned dairy manure compost than in rice husks, and the largest was returned swine manure compost. Therefore, if rice husks are used as supplementary material for composting mixture, it is considered that the lower part is not easily affected by the load on the upper part, even if the sedimentation height is high. On the other hand, returned swine manure compost had a high bulk density and was easily affected by load. Although it has a function of adjusting moisture when used as supplementary material, it is expected that it is unlikely to lead to a decrease in bulk density, that is, an increase in air space.

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