PRODUCTION OFEDIBLE OYSTER MUSHROOM SPECIES (pleurotus ostreatus, pleurotus sajor-caju, pleurotus florida)USING COFFEE(coffea arabica L.) HUSK AND KHAT(Catha edulis) LEAF AS GROWTH SUBSTRATES

Biogas technology, which is meant to produce methane rich gas through anaerobic digestion of biological materials, is an environmentally friendly technology that reduces emission of green house gases. Therefore, this research was initiated to utilize biomasses such as barley straw (BS) and goat manure (GM) for biogas production. In this study, biogas production from co-digestion of the BS and GM in five mix ratios (100%BS, 75%BS: 25%GM, 50%BS: 50%GM, 25%BS: 75%GM and 100%GM mix) were evaluated by incubating at 38ºC using batch fermentation after the substrates were pre-treated with temperature of 60 and 80°C separately. In all treatments, physico-chemical parameters such as total solid (TS), volatile solid (VS), organic carbon, total nitrogen, carbon to nitrogen ratio and pH were measured before and after anaerobic digestion (AD). Gas production was noticed in all of the digesters from day 1st of AD. The daily biogas production was subsequently measured by water displacement method for 21 days. Higher daily mean biogas amount was produced at day 3rd and 4th for all substrates which were thermally pre-treated under 80 and 60°C, respectively and went down to zero at about the 21st days almost in both thermal pre-treated substrates. Out of the five treatments, treatment 4 (T4=25%BS: 75%GM mix ratio) has produced high cumulative amount of biogas in both 60 and 80°C thermal pre-treatments (1185.33 and 1442.67mL, respectively). Better cumulative biogas yield was observed on the treatments pretreated under 80°C than 60°C. Highest reductions of TS (22.77%) and VS (36.23%) were recorded in T4 pre-treated at 80°C. The result also revealed that co-digestion enhances the production of biogas and an increment of biogas was observed with the increment of the GM concentration in the co-digestion. Generally, the T4 was the best mix among all other treatments which produced high cumulative biogas in 80°C thermal pre-treatment (1442.67mL).