Influence of Inoculums Source and Pretreatment on Biogas Production from Cashew Nut Shells (Anacardium occidentale)

Bioenergy recovery from cashew nut shells was investigated throughout using efficient inoculums source and appropriate pretreatment. Physicochemical characteristics of shells and inoculums including pH, volatile fatty acid (VFA, total solid, volatile solid, ash were determined using standard methods. Total anaerobes and methanogenic archaea from inocula were determined by MPP method. Wastewater (WW), sludge from bioreactor (SBR), bovine dung (BD) and mixed inoculums (MIX) were used to evaluate inoculums source in batch system. Biochemical methane potential of pretreated shells was evaluated. Biogas was measurement by liquid displacement. CH4 and CO2 were performed by GC. MIX and WW showed high concentration of methanogenic bacteria (2.3 102 CFU/mL). Best biomethane levels 70.38% with yields of 55.52 L biogas. (Kg VS)-1 was observed with old shells inoculated by MIX. Low productivity was noted with thermal and biological treatment of old and fresh shells, 11.20 and 0.02 L CH4. (Kg VS)-1, respectively. Inoculums source has significant effect on biogas production. Mixed inoculums exhibited significantly high yields of biomethane. Thermo-biological pretreatment seems to be not appropriate for a better biomethane production. Combination of thermochemical and biological pretreatment could be necessary for best biomethane production yield.