Modelling the effects of particle size pretreatment method on biogas yield of groundnut shells

Optimising biogas yields from anaerobic digestion of organic wastes is significant to maximum energy recovery in the biodigestion process and has become an important topic of interest. Substrate particle size is an important process parameter in biogas production, and it precedes other pretreatments methods for the majority of the lignocellulose materials. Optimisation of biogas yield using Response Surface Methodology (RSM) was done, and temperature, hydraulic retention time and particle size were considered variables to develop the predictive models. Pretreatment of groundnut shells was investigated using particle size reduction of mechanical pretreatment methods. After pretreatment, 30 samples were digested in a batch digester at mesophilic temperature. The experimental results showed that the temperature, hydraulic retention time and particle size had significant effects of interaction (p < 0.05). The optimum experimental and predicted yields are: 44.70 and 42.92 (l_NkgoDM) organic dry matter biogas yield, 20.80 and 19.09 (l_N/kgFM) fresh mass biogas yield, 24.00 and 22.68 (l_NCH₄oDM) organic dry methane yield and 12.30 and 15.59 (l_NCH₄FM) fresh mass methane yield, respectively. The R² recorded for the four yield components were 0.6268, 0.5875, 0.6109 and 0.5547. These values seem to be lower and a sign of the average fit of the model. Biogas production from groundnut shells was significantly improved with statistical optimisation and the pretreatment method.