An Evaluation of a Batch Pilot-Scale Digester for Gas Production from Agricultural Wastes

Abstract

A batch pilot-scale biogas reactor was fabricated using 3 mm mild steel. It was a horizontal, cylindrical digester measuring 58 cm (diameter) by 106 cm (length) of total volume 0.28 m 3 . This package facility was easy to install and operate, consisting of several components that can be assembled and put to use much like a do-it-yourself kit. During a forty-day anaerobic digestion of four types of agricultural wastes (poultry droppings, cow dung, corn stalk and mixed substrate), the biogas production from each waste was determined using the water displacement method via batch operation. 38.49 kg (wet weight) of substrate mixed with water in the ratio of 1:1 was used as feed. The results showed that the average daily gas production from poultry droppings, 137.16 liters, was the highest, while corn stalk produced the least, 16.38 liters. Laboratory analysis showed that the biogas produced contained 60% methane while carbon dioxide and other trace gases made up the balance of 40%. The gas produced burnt well in a Bunsen burner with a blue flame. The gas production was good and is a practical indicator of the performance of the digester. A maximum reactor pressure of 1.34 bars was recorded for a period of seven days of no gas harvest when poultry droppings were used as substrate, indicating that biogas production in a reactor is a relatively low-pressure operation.