Substrate-inoculum Ratio Optimization upon the Biogas Production from Peels of Eggplant and Cassava by Biomethanization

Abstract

In this work we have highlighted the importance of substrate-inoculum ratio on the biogas (biomethane) production when using peels of eggplant and that of cassava by biomethanization method. The study has been designed as follow: digestion of pig manure (inoculums) produced under anaerobic conditions; degradation of organic wastes (substrate) and measures of cumulative volumes of biogas produced, respectively. The study was conducted at the Department of Chemistry and Faculty of Oil and Gaz, University of Kinshasa, DR Congo, from February 2013 to May 2016. Standard method of serum bottles liquid displacement systems was used to measure cumulative volumes of biogas produced each day. Digested pig manure was utilized as inoculum and peels of eggplant and that of cassava as substrate sources. Previously, the inoculum was characterized.  The inoculum physico-chemical parameters are: (93.27±0.27)% of moisture, (69.46±2.23)% of ash, (30.54±3.27)% of volatil solids and (6.73 ± 0.26)% of total solids. During 14 days of biogas production, the results of cumulative volumes of biogas produced showed that methanogenic bacteria exhibited high biodegradation activity of peels of eggplant than the one of cassava. And for the two cases a substrate-inoculum ratio of 50% produced high amount of biomethane. From the ratio 50% and progressively decreasing the amount of inoculum the yield also decreased proportionately. Weak biodegradation activity of peels of cassava could be explained as an occurrence of cyanide that is toxic to the methanogenic bacteria. Therefore for an optimal production of biomethane from peels of cassava a preliminary deep step of pretreatment is required for the removal of cyanide in order to improve the production yield. The substrate-inoculum ratios as well as pretreatment of substrate are valuable for an optimal yield of biomethanization.