Optimisation of the anaerobic co-digestion process of Calotropis procera leaves, stems, and cow dung using a mixture design

Abstract

Batch tests were carried out to evaluate the biogas production potential of the co-digestion of Calotropis Procera and cow manure. An augmented simplex centroid design was used to establish the mixture proportions for the co-digestion process. Cow dung, Calotropis procera leaves, and Calotropis procera stems were the three components that went into forming the mixtures. Before and after the digestion process, each mixture combination was analyzed for Total Solids content, Volatile Solids content, and pH. Cumulative biogas production, cumulative methane yield, and the percentage of volatile solids reduction were the responses utilized to evaluate the performance of the reactors. The Response Surface Methodology was used in order to determine the optimal combination that would result in the maximum amount of biogas and bio-methane generation. Contour, 3D surfaces and residual plots were used to locate and display the regions that showed the best performance in terms of responses. The results showed that the optimal proportions for maximum biogas yield, cumulative methane production, and percentage reduction in volatile solids were 17.17% leaves and 82.83% stems. The study has thus revealed that the co-digestion of Calotropis Procera leaves with stems is more significant than that of the mixtures containing cow dung. The findings of this study suggest that although the co-digestion of Calotropis Procera with cow dung is a viable solution for improving the biogas production, the co-digestion of Calotropis Procera leaves and stems has a higher yield.

Keywords

• Calotropis procera
• Anaerobic co-digestion
• Mixture design
• Response surface methodology