Biogas production using conventional plastic water tank digester

Article ID: 269

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Abstract

Agricultural biomass is an essential source of clean energy, particularly through technologies like anaerobic fermentation, which is used to produce biogas. This clean energy can replace fossil fuels, helping to reduce dependency on non-renewable resources. This project focuses on the design of a 0.5 m³ fixed dome plastic biogas digester, a manual biogas compressor, and biogas production from domestic biodegradable waste such as dry leaves, kitchen waste, and grass. The experiment involved mixing 120 kg of biodegradable waste with 300 kg of water and feeding it into the digester. Three batch experiments were conducted over three months. The first two months did not yield successful results, but in the third month, the digester produced 1 kg of biogas at an ambient temperature of 34 ℃ to 35 ℃. Negative pressure was observed at the start, indicating some aerobic digestion before anaerobic digestion began. The maximum pressure in the digester reached 7172.75 Pa on day nine, with a gas yield of 0.15 kg on the same day. Combustible gas production started after 20 days, and the gas produced over the next 30 days was compressed into cylinders for mobility. This success highlights the potential of biogas technology to contribute to the energy mix and address current energy challenges. The study also investigates the performance and durability of PVC (polyvinyl chloride) used in biogas digesters over a three-month period, considering long-term environmental exposure. PVC is a widely used thermoplastic polymer, known for its chemical resistance, cost-effectiveness, and strength. These properties make it suitable for small- to medium-scale digesters, particularly under mesophilic conditions (35 ℃–40 ℃). The PVC digester-maintained gas retention and structural integrity without significant degradation during the observation period. However, long-term exposure to UV radiation and thermal fluctuations presents challenges, as PVC degrades under UV exposure, leading to brittleness and cracking. Prolonged exposure to high temperatures may also cause PVC to soften, especially in thermophilic conditions (>50 ℃). Predictions suggest that PVC digesters could last 5–8 years with UV protection and under optimal conditions. Without UV stabilization or in harsh environments, their lifespan may be reduced to 2–4 years. Regular maintenance, temperature management, and UV protection are crucial for extending the durability of PVC-based digesters.