Optimization of the methane production from Mangifera Indica (mango) and Manihot Utilissima (cassava) leaves in co-digestion

Abstract

Leaves of Mangifera indica (MI, mango leaves) and Manihot utilissima (MU, cassava leaves) are available in tropical regions and are the most accessible vegetable waste of Kinshasa Province, capital of the Democratic Republic of Congo. The main objective of this study was to investigate the optimization of methane production from MI and MU leaves in co-digestion by BMP tests at 30°C. The yields for 100 days achieved from the anaerobic digestion of up to 61.3 g raw matters in 1 l medium were 0.001 l/g and 0.100 l CH4/g volatile solids of MI and MU leaves respectively. By comparison to MI, MU leaves are generally characterized by a higher in mineral content. The TOC and TKN related to MU were slightly lower and 6-fold higher respectively than the corresponding levels in MI. Therefore, the carbon to nitrogen ratio C/N, i.e. about 7, was significantly different regarding the range from 20 to 30 commonly recommended for optimal anaerobic digestion. The reason why, MU and MI leaves were mixed for correcting their C/N ratios. Therefore, leaves yields of methane production in relation to volatile solids were improved. The MU and MI yields in the mixture of MU (75%) and MI (25%) have increased; they were 0.121 l/g and 0.114 l CH4/g volatile solids respectively or nearly 1-fold higher and nearly 100-fold higher respectively than the corresponding leaves in the isolated digestion