Design and fabrication of 3.60 m3 household plastic bio digester loaded with kitchen waste and cow dung for biogas generation

Abstract

A 3.6 m 3 pilot plastic digester for family generation of biogas was designed, constructed and evaluated through physico-chemical studies using 50% cow dung and 50% kitchen wastes. The ash content of waste increased after digestion while the fibre and fat contents of the waste was 5.10 and 1.05% but significantly (p<0.05) decreased to 2.49 and 0.70% after digestion. The carbohydrate content of the waste was 11.02% which significantly (p<0.05) decreased to 7.91%. The volatile solid content of 50% cow dung + 50% cassava peel + yam peels + vegetable was 11.10%. The biochemical oxygen demand was 44.58% while the chemical oxygen demand was 139.20% before digestion but decreased significantly (p<0.05) after digestion. The pH of 50% cow dung + 50% cassava + yam peels + vegetable waste during digestion increased from 6.71 at day of charging to 6.81 at the 8th day after which it began to fluctuate between 6.68 and 6.85 throughout the retention period. Afternoon temperatures of both ambient and slurry were within the mesophilic (30 and 40°C) temperature which was higher than the morning and evening temperatures. The production of biogas started at the 2nd day by producing 406 L and increased each day till day 8, by producing 738 L and after which its production began to fluctuate between 572 and 718 L/day. Early biogas flammability was observed on the 4th day for 50% cow dung + 50% cassava + yam peels + vegetable. At the point of flaming, the methane content of the biogas increased significantly (p<0.05) to 65.65%, while the carbon dioxide decreased significantly (p<0.05) to 25.15%, for 50% cow dung + 50% cassava + yam peels + vegetable. The average biogas (0.601 to 0.505 m 3 /day) produced from the waste using 3.6 m 3 capacity plastic bio-digester could be sufficient to cook three times a day for household of 3 to 4 persons.

Development of a Batch-Type Biogas Digester Using a Combination of Cow Dung, Swine Dung and Poultry Dropping

“…The mesophilic (21˚C -38˚C) is the temperature range that was identified from the slurry temperature. This is similar to the result observed by Otun et al [7] and Nwanko et al [11]. From the results obtained, anaerobic bacteria thrive best at a mesophilic temperature of about 34˚C [27] [40].…”

“…It was also observed that the changes in the pH value also resulted in changes in the volume of gas produced, as consistency in the higher range of pH favours the methanogenic bacteria. These bacteria are inhibited in pH greater than 8 or less than 5 as reported by Nwanko et al [11] and Okewale [40]. Figure 2 shows the slurry temperature trend of the mixed substrates.…”

“…It is obvious that the moisture, ash content and pH increased significantly (p < 0.05) while the total solids, volatile solids and the temperature reduced significantly (p < 0.05) as also observed by Nwankwo et al [11]. Although the total solid content of the waste used was above the optimum range of 7% -9% recommended by Nwankwo et al [11] and Deepanraj, et al [37] in order to avoid overloading the system. However, the digestion process was efficient in removing the total solid.…”

“…From the experiment, it was revealed that the acidity in the digester caused the very low yield of biogas in the first 7 days of retention. The result was compared to some other results obtained previously by Musa and Raji [10] from the analysis of biogas from three organic wastes, Ukpabi [30] who produced biogas from cow dung and food waste, Nwanko et al [11] who generated biogas from kitchen waste and cow dung, and Otun et al [7] who evaluated the production of biogas from the co-digestion of animal, food and fruit waste.…”

“…Achieving solutions to probable scarcity of fossil fuels and environmental problems that the world is facing today requires long-term potential actions for sustainable development [9] [10] [11]. The dependence on fuel wood for the domestic energy supply has aggravated deforestation, with annual deforestation rate estimated at 3%, which is equivalent to the loss of 410,000 hectares of forested land annually.…”