Trends in biotechnological production of fuel ethanol from different feedstocks.

An overview of the different inhibitors formed by pre-treatment of lignocellulosic materials and their inhibition of ethanol production in yeast and bacteria is given. Different high temperature physical pre-treatment methods are available to render the carbohydrates in lignocellulose accessible for ethanol fermentation. The resulting hydrolyzsates contain substances inhibitory to fermentation—depending on both the raw material (biomass) and the pre-treatment applied. An overview of the inhibitory effect on ethanol production by yeast and bacteria is presented. Apart from furans formed by sugar degradation, phenol monomers from lignin degradation are important co-factors in hydrolysate inhibition, and inhibitory effects of these aromatic compounds on different ethanol producing microorganisms is reviewed. The furans and phenols generally inhibited growth and ethanol production rate (QEtOH) but not the ethanol yields (YEtOH) in Saccharomyces cerevisiae. Within the same phenol functional group (aldehyde, ketone, and acid) the inhibition of volumetric ethanol productivity was found to depend on the amount of methoxyl substituents and hence hydrophobicity (log P). Many pentose-utilizing strains Escherichia coli, Pichia stipititis, and Zymomonas mobilis produce ethanol in concentrated hemicellulose liquors but detoxification by overliming is needed. Thermoanaerobacter mathranii A3M3 can grow on pentoses and produce ethanol in hydrolysate without any need for detoxification.

Inhibition of ethanol-producing yeast and bacteria by degradation products produced during pre-treatment of biomass.

Microalgae are a diverse group of prokaryotic and eukaryotic photosynthetic microorganisms that grow rapidly due to their simple structure. They can potentially be employed for the production of biofuels in an economically effective and environmentally sustainable manner. Microalgae have been investigated for the production of a number of different biofuels including biodiesel, bio-oil, bio-syngas, and bio-hydrogen. The production of these biofuels can be coupled with flue gas CO2 mitigation, wastewater treatment, and the production of high-value chemicals. Microalgal farming can also be carried out with seawater using marine microalgal species as the producers. Developments in microalgal cultivation and downstream processing (e.g., harvesting, drying, and thermochemical processing) are expected to further enhance the cost-effectiveness of the biofuel from microalgae strategy.

https://aiche.onlinelibrary.wiley.com/doi/pdf/10.1021/bp070371k

Biofuels from microalgae.

Alternatives for detoxification of diluted-acid lignocellulosic hydrolyzates for use in fermentative processes: a review

Perspectives on microalgal CO2-emission mitigation systems - A review

Economical production of cellulase enzyme is key for feasible bioethanol production from lignocellulosics using an enzyme-based process. On-site cellulase production can be more feasible with the process of separate hydrolysis and fermentation (SHF) than with simultaneous saccharification and fermentation, since the cost of enzyme is more important and a variety of substrates are available for the SHF process. Cellulase production using various biomass substrates available for SHF, including paper sludge, pretreated wood (steam exploded), and their hydrolysis residues, was investigated in shake flasks and a fermenter for their productivities and titers. Among the newspaper sludge, office paper sludge, and steam-exploded woods treated in various ways, the steam-exploded wood showed the best properties for substrate in cellulase production. The best titer of 4.29 IU/mL was obtained using exploded wood of 2% (w/v) slurry in the shake flask, and the titer with the same substrate was duplicated to about 4.30 IU/mL in a 3.7-L fermenter. Also, the yield of enzyme reached 215 IU/g of substrate or 363 IU/g of cellulose. Despite various pretreatment attempts, newspaper and office paper substrate was inferior to the exploded-wood substrate for cellulase production. However, hydrolysis residues of papers showed quite promising results. The hydrolysis residue of office paper produced 2.48 IU/mL of cellulase in 7 d. Hence, the utilization of hydrolysis residues for cellulase production will be further investigated in the future.

Enzyme production of Trichoderma reesei Rut C-30 on various lignocellulosic substrates.

Ethanol production from concentrated oak wood hydrolysate was carried out to obtain a high ethanol concentration and a high ethanol yield The effect of added inhibitory compounds, which are typically produced in the pre-treatment step of steam-explosion on ethanol fermentation, was also examined p-Hydroxybenzoic aldehyde, a lignin-degradation product, was the most inhibitory compound tested in this study Compounds with additional methyl groups had reduced toxicity and the aromatic acids were less toxic than the corresponding aldehydes The lignin-degradation products were more inhibitory than the sugar-derived products, such as furfural and 5-hydroxymethylfurfural (HMF) Adaptation of yeast cells to the wood hydrolysate and detoxification methods, such as using charcoal and overlime, had some beneficial effects on ethanol production using the concentrated wood hydrolysate After treatment with charcoal and low-temperature sterilization, the yeast cells could utilize the concentrated wood hydrolysate with 170 as well as 140 g/L glucose, and produce 699 and 742 g/L ethanol, respectively, with a yield of 046–048 g ethanol/g glucose In contrast, the cells could not completely utilize untreated wood hydrolysate with 100 g/L glucose Low-temperature sterilization, with or without charcoal treatment, was very effective for ethanol production when highly concentrated wood hydrolysates were used Low-temperature sterilization has advantages over traditional detoxification methods, such as using overlime, ion exchange, and charcoal, because of the reduction in the total cost of ethanol production

Ethanol production using concentrated oak wood hydrolysates and methods to detoxify.

Possible methods to minimize the toxic effects of SOx and NOx on the growth of a highly CO2 tolerant and fast-growing microalga, Chlorella sp. KR-1, were investigated. Maintaining the pH of the culturing media at an adequate value was quite important to enhancing the tolerances of the microalgae to SOx and NOx. Controlling the pH by adding an alkaline solution, using a low flow rate of gas fed to the culture, and using a high concentration of inoculating cells were effective methods to maintaining the proper pH of the culture. Controlling the pH was the most effective method but could be applied only for some specific microalgae.

Methods to Enhance Tolerances of Chlorella KR-1 to Toxic Compounds in Flue Gas

The growth capabilities of three highly-CO 2 -tolerant microalgae under high concentrations of CO 2 were compared for their tolerance to SO 2 and NO, the major inhibitory compounds present in flue gases. Although all strains showed good growth with 15% CO 2 , Chlorella KR-1 exhibited the most desirable properties for CO 2 fixation among the strains compared. While Chlorella sp. HA-1 exhibited the best tolerance to NO among the algal strains tested, Chlorella sp. KR-1 showed higher tolerance to SO 2 than the other two strains tested.

Effects of NO and SO2 on growth of highly-CO2-tolerant microalgae

The effect of the non-ionic surfactants on the ethanol fermentation was greatly dependent on the surfactant added. While Tween 20 and Tween 80 slightly enhanced ethanol fermentation, Triton X-100 which exhibited the inghest increase in the enzymatic saccharification had a negative effect on the ethanol fermentation. The negative effect of Triton X-100 on ethanol production was the most pronounced when the cellulosic hydrolyzates were used. Tween 80 showed the best performance for the ethanol production from steam exploded wood hydrolyzate.

Chul Seung Shin

Papers

Enzyme production of Trichoderma reesei Rut C-30 on various lignocellulosic substrates.

Ethanol production using concentrated oak wood hydrolysates and methods to detoxify.

Methods to Enhance Tolerances of Chlorella KR-1 to Toxic Compounds in Flue Gas

Effects of NO and SO2 on growth of highly-CO2-tolerant microalgae

Effect of surfactants on ethanol fermentation using glucose and cellulosic hydrolyzates