Biochemical methane potential of Jatropha curcas fruit shell: comparative effect of mechanical, steam explosion and alkaline pretreatments

Jatropha curcas is a promising tropical and subtropical plant species for biodiesel production that can reduce the competition between food and energy production. Jatropha seed processing for oil extraction usually generates considerable amount of Jatropha curcas fruit shell (JCFS), which can be considered as a potential substrate for biogas production rather than being discarded as solid waste. However, the higher lignocellulosic constituents in JCFS potentially affect the biological degradation process. Thus, applying suitable pretreatment techniques in advance of anaerobic digestion could enhance the biodegradability and methane yield of JCFS. In this study, the effect of mechanical, steam explosion (SE), and alkaline pretreatments on the chemical composition and methane yield of JCFS was examined at various process conditions. As compared with the untreated sample, grinding the JCFS into a particle size of less than 1 mm increased the methane yield by 74.23%, while at the optimum SE pretreatment process (160 degrees C, 5 min), the methane yield was increased by 54.75%. The alkaline pretreatment was relatively less effective over the other pretreatments; 44.05% methane yield increment was achieved after soaking the JCFS with 7.32% NaOH at 36 degrees C for 54 h. The effect of SE on compositional change depends on the severity factor in which severe pretreatment conditions were adequate for solubilizing the hemicellulose but resulted in higher pseudo-lignin and lower methane yields. In conclusion, all pretreatments processes have significantly increased the methane yield of JCFS as compared to the untreated JCFS; however, mechanical pretreatment was more effective than SE and alkaline pretreatments.

Automated summary

Jatropha curcas fruit shell (JCFS) can be a potential substrate for biogas production, but suitable pretreatment techniques are needed to enhance its biodegradability and methane yield. Mechanical pretreatment showed the highest methane yield increment, while steam explosion (SE) and alkaline pretreatments also had positive effects, though less effective.