Production of bioenergy from rice-melon husk co-digested with cow dung as inoculant

Abstract

Anaerobic digestion of energy crops, residues, and wastes is of increasing interest in order to reduce the greenhouse gas emissions and to facilitate a sustainable development of energy. Production of bioenergy provides a versatile carrier of renewable energy, as methane can be used for replacement of fossil fuels in both heat and power generation. Biogas was produced from co-digestion of rice husk (RH), melon husk, (MH) and cow dung (CD) for 200 days at different rice-melon husk (RH:MH) ratios. Fixed quantity of cow dung slurry was added to each treatment as inoculant to seed the digesters. A mixture-process variable design was used to formulate biogas production from different biomaterials. Concentration of NaOH was varied from 8 to 9% while total solids were also varied within a range of 8% to10%. Initial properties of RH, MH and CD were determined. Melon husk was found to be the densest with total solids (96.9%), followed by rice husk (91.8%) then cow dung (16%). In terms of volatile solids, cow dung and melon husk have values close to each other (96.4% and 89.5% respectively), rice husk recorded lower value (79.2%). RH:MH (100:0) recorded the highest biogas yield (606.933 mL kg-1) while RH:MH (0:100) recorded the least biogas yield (376.533 mL kg-1). Biodegradation and maximum biogas yield models based on first-order kinetics were fitted to the experimental biogas yields to predict maximum biogas yields from each treatment. The high R2 values showed that the biodegradation model and the maximum biogas yield model predicted the maximum yields adequately. Biogas yield from RH:MH (0:100) was the best described and predicted by the biodegradation model while biogas yield from RH:MH (100:0) was best described by the maximum yield model. Keywords: rice husk, melon husk, agro-residue, biodegradation model, co-digestion, biogas yield