Production of biogas using small-scale plug flow reactor and sizing calculation for biodegradable solid waste

Abstract

Experiment was conducted on the fabricated biodigester of capacity 30 l. Slurry of cow manure in water was fed through the inlet until the digester is about 80% filled with slurry, and the slurry surface on both inlet and outlet did not leave holes by which the air can get into the digester. This was to ensure the anaerobic condition in the gas space inside the digester. After the first filling, both the inlet and outlet were covered and gas valve to the gas holder was opened. In the first 20 days, the gas holder expanded with produced gas. The first 20 days was the transient phase of the biogas production and it acted as a batch reactor. At the end of 20 days, the content of the gas holder was released as it did not burn due to the predomination of carbon dioxide. The next phase was started wherein the biodigester was fed periodically with slurry including kitchen and domestic waste from the M.S. Ramaiah Institute of Technology college canteen and hostels. After the digester was operational for several weeks (in reactor from which inoculation charge is obtained) and after the initial filling, the pH value had reached the stable value of 6.5 that remained constant during the period of sampling. The temperature was constant between 35 to 40 during the day and 25 to 30 during the night. Therefore, those two parameters were considered as the constants with respect to the model development. Based on our field data, those two parameters did not fluctuate significantly in Bangalore climate (where plug flow reactor is operated).