A study on bioethanol production from cashew apple pulp and coffee pulp waste

Bioethanol production from dry cashew apple pulp and coffee pulp was investigated. The pulp was digested with 2% sulfuric acid and subjected to high pressure (15 psi) cooking at 120 °C for 10 min followed by further 1 and a half hour pressure cooking at 90 °C to solubilize the pulp. Solubilized pulp was filtered and the debris on the filter paper was washed with minimum quantity of distilled water and then oven dried to find the weight of the insoluble lignin mass. Total sugar content in squeezed and dried cashew apple pulp (CAP), dry coffee pulp (DCP) and wet coffee pulp (WCP) was found to be 2.12, 1.62 and 0.62 g/100 ml of hydrolyzate. Reducing sugar content in squeezed CAP, DCP and WCP was found to be 0.14, 0.71and 0.23g/100 ml of hydrolyzate. Filtrate was neutralized with thick suspension of calcium hydroxide slurry until the pH reaches to 6.0. Neutralized slurry was kept at lab temperature overnight and the supernatant was decanted through filter paper. To 150 ml of filtrate yeast (Saccharomyces creviciae) was added at a concentration of 5.0 g/l concentration and subjected to fermentation for 48 h at 30 °C in a shaker incubator at 120 rpm. Ethanol content in the fermented broth was estimated by titrimetric and gas chromatographic method. Ethanol yield in the fermented broth was found to be 0.5, 0.46 and 0.46 g/g of sugar in squeezed CAP, DCP and WCP. Theoretical ethanol yield (Ymax%) of squeezed CAP, DCP and WCP was found to be 46, 9.35 and 40% respectively.