INVESTIGATING THE EFFECCT OF TEMPERATURE ON BIOGAS PRODUCTION USING DIFFERENT DOMESTIC ORGANIC WASTES

Abstract

Biogas is one of the renewable energy sources and has a potential to overcome the problem of organic waste accumulation. Biogas technology used to provide biofuel energy, reduce organic waste and produce organic fertilizers. Organic waste management system in Ethiopia is not well developed and as result in large city like Addis Ababa is facing the problem of organic waste accumulation on land and water drainages. Thus, this study has focused in biogas production through anaerobic digestion of domestic organic wastes such as fruits, vegetables and food wastes to alleviate waste accumulation problems and enhance optional energy production. Organic wastes were collected from hotels, domestic and waste dumping sites. To make stable pH and better methanogen activity, fruit waste at C:N (36:1) was mixed in equal proportion with low carbon waste ratios [food waste (29:1), cow dung (23:1) and vegetable (25:1)] to reduce its C:N (28:1) ratio served as mixed waste. Five treatments (fruit, food, cow dung, vegetable and mixed waste) which contain 350 g for each treatment was fed into 0.5 L digester. Then, to investigate the effect of temperature on biogas production each treatment was kept at constant temperature of 20°C, 37°C and 45°C using water bath for 25 days. Every five day intervals biogas production was measured using syringe. The highest biogas yield (39.82ml/g) was from mixed waste at 45°C. Thus, mixed waste produced more biogas than other wastes because the C:N could be adjusted by different organic materials. The correlation between biogas production and temperature was positively strong (r= 0.66, P<0.05). Biogas production was significantly different in the three temperature treatments (P=0.03). After the biogas was produced, potassium and sodium hydroxide solutions were used to purify the produced biogas. Thus, the highest purification was found using potassium hydroxide solution. In summary, this study showed that mixed organic waste produced the maximum biogas at 45 C and potassium hydroxide solution was the best solution to purify the produced gas. Further, detail study on the composition of mixed organic waste for longer digestion time would give more comprehensive understanding of the field of biogas technology. o