Optimization of process parameters for anaerobic co-digestion of cow dung and jatropha cake using response surface methodology

¹ Department of Mechanical Engineering Science, Faculty of Engineering and the Built Environment, University of Johannesburg, South Africa.
² Process Energy and Environmental Technology Station, Faculty of Engineering and Built Environment, University of Johannesburg, South Africa.

Abstract

The United Nations Sustainable Development Goals (SDGs) can be achieved with the help of waste-to-energy technology, which utilizes agricultural waste, particularly in developing nations. Anaerobic co-digestion of two or more substrates is gaining popularity due to its ability to increase organic waste management and biogas generation. This work investigates the impacts of three independent input variables of temperature, mixing ratio, and retention time on the biogas released from cow dung (CD) and jatropha cake (JC). Biogas yield was optimized and predicted using a Central Composite Design of Response Surface Methodology (RSM) in an anaerobic co-digestion process. The observed result indicates that the linear model terms of retention time, mixing ratio, and temperature have a significant interactive influence (P ≤ 0.05). The optimal conditions were a temperature of 34 °C, a retention time of 29 days, and a 75:25 % mixing ratio (CD to JC). The model predicted 1.87 L/Kg VS_added at the optimum conditions with a correlation value (R²) of 0.8390. In general, this study has demonstrated that co-digestion of CD and JC is a promising approach to enhance biogas yield by providing a balanced nutrient supply, which can be applied for commercial purposes, and the process can be optimized using RSM.