Abstract
Bioethanol production from corn is a well-established technology. However, emphasis on exploring non-food based feedstocks is intensified due to dispute over utilization of food based feedstocks to generate bioethanol. Chemical and biological conversion technologies for non-food based biomass feedstocks to biofuels have been developed. First generation bioethanol was produced from sugar based feedstocks such as corn and sugar cane. Availability of alternative feedstocks such as lignocellulosic and algal biomass and technology advancement led to the development of complex biological conversion processes, such as separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SSCF), consolidated bioprocessing (CBP), and syngas fermentation. SHF, SSF, SSCF, and CBP are direct fermentation processes in which biomass feedstocks are pretreated, hydrolyzed and then fermented into ethanol. Conversely, ethanol from syngas fermentation is an indirect fermentation that utilizes gaseous substrates (mixture of CO, CO2 and H2) made from industrial flue gases or gasification of biomass, coal or municipal solid waste. This review article provides an overview of the various biological processes for ethanol production from sugar, lignocellulosic, and algal biomass. This paper also provides a detailed insight on process development, bioreactor design, and advances and future directions in syngas fermentation.
Highlights
Bioethanol production from corn is a well-established technology
Availability of alternative feedstocks such as lignocellulosic and algal biomass and technology advancement led to the development of complex biological conversion processes, such as separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SSCF), consolidated bioprocessing (CBP), and syngas fermentation
This paper provides a detailed insight on process development, bioreactor design, and advances and future directions in syngas fermentation
Summary
Algal biomass can be used to produce a variety of biofuels such as hydrogen, diesel, isobutene, and ethanol (Cruz et al, 2014; Mussatto et al, 2010; Nayak et al, 2014; Posten and Schaub, 2009). Starch and cellulose are extracted from algae biomass using mechanical shear or by enzyme hydrolysis, after which they are utilized for bioethanol production (John et al, 2011). The conversion technologies of algal and plant based cellulosic biomass to ethanol are similar, which are discussed in sections 2 and 3 of this review article. Cultivation of microalgae through open ponds is economical but has inherent disadvantages such as low productivity, water loss, low CO2 utilization, and high affinity to be contaminated by other algal strains (Chisti, 2007; John et al, 2011; Posten and Schaub, 2009). Ethanol production through hydrolysisfermentation is briefly discussed followed by a detailed review of syngas fermentation process an indirect biomass conversion process to produce bioethanol. Discussion on thermochemical conversion processes can be found elsewhere and is out of scope of this review article (Dutta et al, 2011; Perales et al, 2011)
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