Production of Bioethanol using Waste Fruits under Acid and Alkali Catalytic Hydrolysis: A Review

Abstract

The present world highly depends on petroleum fuels to gain energy for transportation resulting in the vast side of environmental problems such as global warming and air pollution. Due to this, the price of conventional fuel escalating day by day. Accordingly, the world needs renewable, ecologically suitable, cost-effective alternate against fossil fuels. Bioethanol is one of the most usable fuel or fuel additives among the other biofuels. Ingoing qualities of bioethanol such as high-octane number, high oxygen content, and low energy content are revealed that application of bioethanol produced from different types of waste materials feedstock in the transportation and energy sector diminishes environment pollution. It provides a solution for waste management. The world releases a considerable amount of fruits as waste annually. Thereby, fruit waste is the cheapest feedstock to produce bioethanol. Fruit waste such as whole rotten fruits, fruit peels, seeds and other residues consists of cellulose, hemicellulose, lignin, starch and simple sugars. Conversion of cellulose and hemicellulose to ethanol is vital to advance pretreatment and hydrolysis techniques to obtain maximum ethanol content. The production process of bioethanol from fruit waste mainly contains pretreatment; hydrolysis, saccharification, fermentation and ethanol extracting process (distillation) steps. Yeast (S. cerevisiae) is primarily used in the fermentation process because of its high conversion efficiency, cost-effectiveness and feasibility of handling. Considering the optimum configuration for bioethanol production, simultaneous saccharification and fermentation (SSF) is the best commensurate method having maximum bioethanol concentration. The fermentation process could be appreciated through various factors, such as temperature (30-33 ºC), pH of the medium (4-5), time of incubation, feedstock concentration, inoculum size, agitating rate, N sources in the medium to gain high bioethanol concentration.