Bioenergy Science and Technology

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    INVESTIGATING THE BIOGAS PRODUCTION POTENTIAL OF COFFEE CHERRY PROCESSING WASTES CO-DIGESTED WITH ANIMAL MANURE
    (Hawassa University College of Agriculture, 2021) WOLDE MATHEWOS DELKERO
    As the human population is increasing from time to time, the energy demand also increasing in a similar fashion. To meet this energy demand, there is high dependence on traditional biomass and fossil fuel, which are major source of environmental degradation. On the other hand, agricultural and industrial wastes are becoming the sources of air and water pollution due to improper management in which otherwise can be used as a renewable energy sources. Biogas is a renewable alternative energy sources made from bio-wastes and has a huge potential for future energy security and environmental sustainability. In the present investigation a “batch feeding digester” was developed to evaluate the potential use of coffee cherries processing wastes: coffee husk, coffee pulp and their co-digestion with cow dung for biogas production at mesophilic conditions and to analyze the nutrient content of the bioslurry to be used as a bio-fertilizer. In advance of biogas production, feedstock quality parameters such as moisture content, total solid, Volatile solid and carbon to nitrogen ratio was determined using standard methods in order to check biodegradability of substrate and balance of nutrients in the substrate. The biogas production was conducted using laboratory digesters having a capacity of five liter with working volume of four liter, operated for about 35 days in incubator at a temperature of 37 0 C. One way analysis of variance (ANOVA) was performed to compare variations among treatments. The result showed that the values of feedstock quality parameters were within the acceptable range for biogas production. The amount of biogas produced from 1:1 coffee pulp with cow dung, coffee pulp, 1:1 coffee husk with cow dung, cow dung and 1:1 of coffee husk with cow dung and coffee husk with was 372.33 ± 5.0, 349.88 ± 2.65, 320.07 ± 3.54, 291.43 ± 5.07 and 268.55 ± 4.16 ml/g VS, respectively. The result indicates that 1:1 ratio of coffee pulp with cow dung produced higher amount of biogas than coffee pulp alone. Significant differences were observed in biogas production potentials between mono-digested and co-digested treatments at (P<0.05). The quality of biogas in terms of methane content was 60.0, 59.2, 58.4, 57.1, 52% respectively, for cow dung, coffee pulp with cow dung, coffee husk with cow dung, coffee pulp and coffee husk. This shows co-digestion improves biogas yield. Generally, the results encouraged the feasibility of the coffee husk, coffee pulp and their co-digestion with cow dung for biogas production in the study areas. Nitrogen, Phosphorous and potassium of bio-slurry were in the range of 1.8 - 2.25, 0.2-1.7 and 0.49-1.3% respectively. This showed that bio-slurry from all treatments had enough amounts of macronutrients that needed in bio- fertilizer.