Evaluation of biogas production potential from anaerobic codigestion of khat (catha edulis) and food waste with cow dung in jimma town, southwest Ethiopia

Abstract

Biogas is produced by bacteria through the bio-degradation of organic material under anaerobic conditions. The aim of this study was to evaluate biogas production potential from anaerobic codigestion of khat (Catha edulis) and food waste with cow dung. Khat waste, food waste, and cow dung were used for this study. Khat waste samples were collected from khat markets of Jimma town, whereas; food and cow dung were collected from Jimma University College of Agriculture and Veterinary Medicine. Ten treatments with different mixing proportions were conducted from khat waste, food waste, and cow dung. These all treatments were evaluated for their potential of gas production. The gas produced was measured by water displacement method until it stopped to produce any more gas. The CH4 content in the biogas was determined by allowing the gas to pass through a CO2 absorption solution. The physico-chemical parameters were determined in a laboratory-scale bench digester for a total period of 41 days at a mean temperature of 22.5 ± 3 °C monitored by Styrofoam. The mean, standard error of the mean for average biogas yield and methane percentage of the triplications of the ten treatments, and correlation statistics at 5 and 1 % significant level, respectively were carried out using SPSS software. The results in this study indicated that the mean biogas produced in ascending order was T3 (5526 mL), T4 (5855 mL), T9 (6003 mL), T8 (6020 mL), T6 (6218 mL), T7 (6375 mL), T10 (6423 mL), T1 (6823 mL), T6 (7310 mL) and T5 (8565 mL) per 100g fresh mass sample. T5 produced the highest biogas yield. This may be because of its optimum C/N ratio (25:1) and synergistic effects of organic matter in terms of provision of nutrient for the growth of methanogenic bacteria. This study helps to improve energy shortage and is a very promising way to overcome the problem of energy demand and waste treatment of our country (Ethiopia)