Coffee is one of the important crops as its ingredients are being consumed across the continents in a variety of food products and drink forms, and do possess significant economic importance to the coffee producing areas of Ethiopia. Dry coffee processing units generates husk as solid waste which is commonly dumped in the surrounding areas without any treatment. The aim of this study is to evaluate biogas production potentials coffee husk anaerobically co-digested with poultry manure or cow dung. The design of this study had nine treatment mixtures of coffee husk, poultry manure and cow dung co-digested in different ratio in batch-type anaerobic digesters for 30 days under mesophilic condition (38oC). The physico-chemical parameters such as moisture content, total solid, volatile solid, pH, organic carbon, total nitrogen and C: N ratio of the feedstock before anaerobic digestion and bio-slurry after anaerobic digestion were determined following standard procedures. The amount of biogas produced by the process was measured for about 30 days of retention time and statistically significant variations were observed among the treatments. The cumulative biogas yield produced from coffee husk and cow dung co-digested in 1:1 ratio was the highest followed by coffee husk and poultry manure in 1:1 ratio while it was the lowest in 100% poultry manure. Moreover, combination of coffee husk and cow dung in the ratio of 1:1 had showed the highest percent reduction in total solid, volatile solid and organic carbon. Therefore, it can be concluded from the results that anaerobic co-digestion of coffee husk and cow dung in equal proportion appeared to be the best combination for large amount of biogas production and hence recommended for further study at pilot scale.
Keywords: Total solids, volatile solids, coffee husk, poultry manure, cow dung, biogas