Enzymatic hydrolysis and fermentation of seaweed solid wastes for bioethanol production: An optimization study

Studies on bioethanol produced from a variety of non-edible feedstocks have recently gained considerable attention because such production can avoid the conflict between food and fuel. In this study, an attempt was made to investigate the production of bioethanol using low-cost feedstock, namely, seaweed solid wastes obtained after the extraction of κ-carrageenan. The utilisation of seaweed solid wastes will simultaneously help to overcome its disposal problem. Two different processes were used: the SHF (separate hydrolysis and fermentation) process and the SSF (simultaneous saccharification and fermentation) process. For the SHF process, enzymatic hydrolysis was conducted by varying three process variables, substrate concentration, pH and temperature, but a constant enzyme dosage was maintained. The highest glucose yield of 99.8% was obtained at pH 4.8, a temperature of 50 °C and a substrate concentration of 2% (w/v) seaweed solid wastes. With subsequent fermentation, a bioethanol yield of 55.9% was obtained. In contrast, for the SSF process, a yield of 90.9% bioethanol was obtained. From these results, it was determined that the SSF of seaweed solid wastes with Saccharomyces cerevisiae has several advantages over SHF because the former is a simple one-step procedure that can save time, cost and energy consumption while achieving a high yield of bioethanol.