Determining the most appropriate and optimum ratios of Organic waste for Biogas generation from small-scale food processing units

Small scale food processing is characteristic of many enterprises in Uganda. As such, the Food Technology Business Incubation Centre (FTBIC), at Makerere University offers food processing entrepreneurs an opportunity to learn practical skills that are indispensable in food processing value chains. Despite the good intensions, FTBIC organic waste, is a menace and a source of pests. The main goal of this study was to determine the most appropriate and optimum ratios of organic wastes for production of biogas to be converted to meet heating needs of FTBIC. The samples of organic waste were quantified and characterized for their potential to generate biogas. Nine treatments in duplicate without inoculum were selected for production of biogas in the ratios: pineapples and other waste 3:1 (A1), 1:1 (A2), and 1:3 (A3); Mangoes and other wastes 3:1 (B1), 1:1 (B2), and 1:3 (B3); and orange and other wastes 3:1 (C1), 1:1 (C2) and 1:3 (C3). Other wastes included: Irish potatoes, bananas, vegetables, passion fruits water melon, pumpkins, pawpaw, mixed food leftovers and jackfruit. The food/microorganism (F/M) ratio was 0.5 i.e. 1.5 gVS of the substrate was digested with 3 gVS of inoculum. On average, 213.7 kg of organic waste was produced daily from the processing unit. The moisture content (MC), total solids (TS), and volatile solids (VS) for the individual organic wastes ranged from 45 to 97.3% wet basis, 54.4 to 6.3% and 60 to 97.3% respectively. The MC, TS and VS of the treatments ranged from 80.8 to 89.2% wet basis, 10.8 to 19.2 gTS/kg and 923.2 to 952.7 gVS/kg respectively. Orange waste with other waste in the ratio of 3:1 yielded the best performance of food waste for biogas production (0.7 L/gVS). Thus more percentage of orange waste in a mixture of organic waste yielded the highest quantity of biogas.