Optimization of methane yield from co-digestion of alkalipretreated groundnut shells and duck waste using response surface methodology

Abstract

Anaerobic co-digestion of lignocellulose feedstock with livestock waste can assist in overcoming the challenges of digesting lignocellulose and balancing the nutrient contents of the process. This study investigated the optimum conditions for methane yield production from anaerobic co-digestion of alkali-pretreated groundnut shells and duck waste using Response Surface Methodology (RSM). A central composite design of the RSM model with three input variables of retention time, temperature, and substrate mixing ratio was used to set up the anaerobic digestion process. Individual and interactive influence of the three process parameters were examined. The result showed that all three process parameters considered are significant and determine the methane yield. The developed RSM model predicted a daily methane yield of 53.33 mL CH4/g VSadded for optimal conditions of 11 days, 26 °C temperature, and 50: 50 mixing ratio, which is not the same as the optimum methane yield observed from the experiment (54.26 mL CH4/g VSadded) and at different process conditions. Cumulative methane yields of 666.72 and 666.66 mL CH4/g VSadded were predicted and observed, respectively, which shows a very close range. The RSM coefficient of determination (R2) value of 0.8251 (82.51%) was observed, indicating a close fit between the predicted and observed yields. Analysis of variance (ANOVA) p < 0.0001 indicates that the developed model could be helpful in anaerobic co-digestion of lignocellulose materials and livestock waste. This study can be replicated at the industrial scale.