Fermentation-Assisted Saccharification for the Production of Bioethanol from Seaweed

Abstract

Fossil fuel reserves are rapidly depleting and the burning of conventional fuels releases large amounts of carbon dioxide into the atmosphere. Crops which are rich in sugar and starch are the best biomass for conversion to ethanol. However, most of them are edible crops and this competes with their use as food. One promising alternative is bioethanol production from seaweed. One of the major advantages associated with using seaweed is that it can grow in ocean water without the need for arable land. The carbohydrates present in seaweed are not easily broken down and fermented, which is why the full potential yield of sugar from seaweed is not obtained. The conversion of these carbohydrates, along with glucans, into ethanol would increase the yields and concentrations of ethanol produced from seaweeds. Seaweed is subjected to various pretreatment strategies to break down complex carbohydrates into simple, usable sugars. The pretreatment can be of 3 types: physical (including thermal and mechanical), chemical, and biological. These include acid pretreatment, alkaline pretreatment, enzymatic, ball milling, hydrothermal, and ultrasound methods. High monosaccharide yield was reported when commercial cellulase was used for pretreatment of seaweed. A major disadvantage associated with using enzymes is the high cost along with the complex recovery of the enzyme, which negatively impacts the commercial production of bioethanol. Combinatorial pretreatments greatly improve the efficacy of the hydrolysis of the carbohydrates as compared to single technique. Ensuring that the overall environmental footprint of bioethanol production from seaweed remains favorable compared to fossil fuel alternatives is essential.