Seaweed Bioethanol Production: A Process Selection Review on Hydrolysis and Fermentation

Abstract

The rapid depletion and environmental concerns associated with the use of fossil fuels has led to extensive development of biofuels such as bioethanol from seaweeds. The long-term prospect of seaweed bioethanol production however, depends on the selection of processes in the hydrolysis and fermentation stages due to their limiting effect on ethanol yield. This review explored the factors influencing the hydrolysis and fermentation stages of seaweed bioethanol production with emphasis on process efficiency and sustainable application. Seaweed carbohydrate contents which are most critical for ethanol production substrate selection were 52 ± 6%, 55 ± 12% and 57 ± 13% for green, brown and red seaweeds, respectively. Inhibitor formation and polysaccharide selectivity were found to be the major bottlenecks influencing the efficiency of dilute acid and enzymatic hydrolysis, respectively. Current enzyme preparations used, were developed for starch-based and lignocellulosic biomass but not seaweeds, which differs in polysaccharide composition and structure. Also, the identification of fermenting organisms capable of converting the heterogeneous monomeric sugars in seaweeds is the major factor limiting ethanol yield during the fermentation stage and not the SHF or SSF pathway selection. This has resulted in variations in bioethanol yields, ranging from 0.04 g/g DM to 0.43 g/g DM.

Evolution toward the utilization of mango leaves as lignocellulosic material in bioethanol production: A review of process parameter and integrated technologies

“…In addition, this process demands a minimal requirement for a sterilized condition for enzymatic hydrolysis as the elimination of the step to transfer the reducing sugar into different vessel . Furthermore, by combining hydrolysis with fermentation, the number of processing stages can be reduced and eventually lower the investment cost for the entire bioethanol production process …”

“…This statement could be justified by the fact that for the simulteneously utilization of hemicellulose and cellulose as sugar source in bioethanol production. With that, undoubtly SSCF would result a higher ethanol yield compared to SSF for the same amount of substrate which entitles the fermentation technology to be more cost‐efficient . From Table , it could be summarized that despite the type of microorganism and the pretreatment process, SSCF have shown the highest ethanol yield compared to SHF and SSF.…”

“…74 Furthermore, by combining hydrolysis with fermentation, the number of processing stages can be reduced and eventually lower the investment cost for the entire bioethanol production process. 75 Inevitably, SSF carried out using wild-type strain of S. cerevisiae is unable to ferment pentose, and this reducing sugar will be marked as biomass waste and subsequently reduces the bioethanol yield. 76 Apart from this drawback, problem also arises in setting a compatible condition for an optimal occurrence of saacharification and fermentation simultaneously.…”

“…With that, undoubtly SSCF would result a higher ethanol yield compared to SSF for the same amount of substrate which entitles the fermentation technology to be more cost-efficient. 75 From Table 6, it could be summarized that despite the type of microorganism and the pretreatment process, SSCF have shown the highest ethanol yield compared to SHF and SSF. Therefore, this process could be considered as a definite solution for long-term bioethanol production.…”

Optimization of an Industrial Medium from Molasses for Bioethanol Production Using the Taguchi Statistical Experimental-Design Method

“…Thus, the importance of microbial production of bioethanol has risen for many years. Efforts on the intensification of the microbial bioethanol production are continued [4]. The optimization of an industrial medium is one of the ways to increase bioethanol production.…”