Co-digestion of Hyptis suaveolens (bushmint) and poultry manure for energy generation: Effects of pretreat-ment methods, Modelling and process parameter optimization study

The potentials of anaerobic co-digestion of poultry dropping with chemically pretreated and untreated Hyptis suaveolens (bushmint weeds) shoots for biogas generation, as well as the process optimization after using a combination of mechanical and thermo-alkaline pretreatment methods, were assessed in this study. Inoculum from cattle rumen content was used to anaerobically digest the shoots. A batch experiment was designed by the Central Composite Design (CCD). Standard procedures were used to assess the physicochemical parameters of the substrates and inoculum, as well as the components of the generated biogas. For the chemically pretreated and untreated tests, the experimental biogas yields were 0.7652 L/kg VS and 1.1396 L/kg VS, respectively. The methane and carbon dioxide content of biogas from both experiments was 69.08%; 17.64% and 62.13%; 21.39% respectively. The Response Surface Methodology (RSM) was employed in data optimization. The predicted biogas yield was 0.7652L/kg VS in the chemically treated experiment, and the model's coefficient of determination (R2) was high (0.9159), indicating strong modeling and prediction accuracy for the chemically treated experiment. There was a 11.19% increase in methane gas yield in the chemically treated experiment over the untreated. The study recommended the worldwide usage of Hyptis suaveolens shoots for biofuels generation and several combinations of pretreatment methods to improve biogas yields.