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Effect of post-treatment process of microalgal hydrolysate on bioethanol production.

ABSTRACT: Microalgae accumulate abundant lipids and are a promising source for biodiesel. However, carbohydrates account for 40% of microalgal biomass, an important consideration when using them for the economically feasible production of biodiesel. In this study, different acid hydrolysis and post-treatment processing of Chlorella sp. ABC-001 was performed, and the effect of these different hydrolysates on bioethanol yield by Saccharomyces cerevisiae KL17 was evaluated. For hydrolysis using H₂SO₄, the neutralization using Ca(OH)₂ led to a higher yield (0.43 g ethanol/g sugars) than NaOH (0.27 g ethanol/g sugars). Application of electrodialysis to the H₂SO₄?+?NaOH hydrolysate increased the yield to 0.35 g ethanol/g sugars, and K⁺ supplementation further enhanced the yield to 0.41 g ethanol/g sugars. Hydrolysis using HNO₃ led to the generation of reactive species. Neutralization using only NaOH yielded 0.02 g ethanol/g sugars, and electrodialysis provided only a slight enhancement (0.06 g ethanol/g sugars). However, lowering the levels of reactive species further increased the yield to 0.25 g ethanol/g sugars, and K⁺ supplementation increased the yield to 0.35 g ethanol/g sugars. Overall, hydrolysis using H₂SO₄?+?Ca(OH)₂ provided the highest ethanol yield, and the yield was almost same as from conventional medium. This research emphasizes the importance of post-treatment processing that is modified for the species or strains used for bioethanol fermentation.

SUBMITTER: Seon G

PROVIDER: S-EPMC7542428 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

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Effect of post-treatment process of microalgal hydrolysate on bioethanol production.

Seon Gyeongho G Kim Hee Su HS Cho Jun Muk JM Kim Minsik M Park Won-Kun WK Chang Yong Keun YK

Scientific reports 20201007 1

Microalgae accumulate abundant lipids and are a promising source for biodiesel. However, carbohydrates account for 40% of microalgal biomass, an important consideration when using them for the economically feasible production of biodiesel. In this study, different acid hydrolysis and post-treatment processing of Chlorella sp. ABC-001 was performed, and the effect of these different hydrolysates on bioethanol yield by Saccharomyces cerevisiae KL17 was evaluated. For hydrolysis using H<sub>2</sub> ...[more]

PMID: 33028886

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Project description:BackgroundMicroalgae have shown clear advantages for the production of biofuels compared with energy crops. Apart from their high growth rates and substantial lipid/triacylglycerol yields, microalgae can grow in wastewaters (animal, municipal and mining wastewaters) efficiently removing their primary nutrients (C, N, and P), heavy metals and micropollutants, and they do not compete with crops for arable lands. However, fundamental barriers to the industrial application of microalgae for biofuel production still include high costs of removing the algae from the water and the water from the algae which can account for up to 30-40% of the total cost of biodiesel production. Algal biofilms are becoming increasingly popular as a strategy for the concentration of microalgae, making harvesting/dewatering easier and cheaper.ResultsWe have isolated and characterized a number of natural microalgal biofilms from freshwater, saline lakes and marine habitats. Structurally, these biofilms represent complex consortia of unicellular and multicellular, photosynthetic and heterotrophic inhabitants, such as cyanobacteria, microalgae, diatoms, bacteria, and fungi. Biofilm #52 was used as feedstock for bioenergy production. Dark fermentation of its biomass by Enterobacter cloacae DT-1 led to the production of 2.4 mol of H2/mol of reduced sugar. The levels and compositions of saturated, monosaturated and polyunsaturated fatty acids in Biofilm #52 were target-wise modified through the promotion of the growth of selected individual photosynthetic inhabitants. Photosynthetic components isolated from different biofilms were used for tailoring of novel biofilms designed for (i) treatment of specific types of wastewaters, such as reverse osmosis concentrate, (ii) compositions of total fatty acids with a new degree of unsaturation and (iii) bio-flocculation and concentration of commercial microalgal cells. Treatment of different types of wastewaters with biofilms showed a reduction in the concentrations of key nutrients, such as phosphates, ammonia, nitrates, selenium and heavy metals.ConclusionsThis multidisciplinary study showed the new potential of natural biofilms, their individual photosynthetic inhabitants and assembled new algal/cyanobacterial biofilms as the next generation of bioenergy feedstocks which can grow using wastewaters as a cheap source of key nutrients.

Project description:In the search for renewable sources of energy, bioethanol stands out as a benchmark biofuel because its production is based on a proven technological platform. Bioethanol is produced mainly from the fermentation of carbohydrates derived from agricultural feedstocks by the yeast Saccharomyces cerevisiae. One of the most widely adopted strains is PE-2, a heterothallic diploid naturally adapted to the sugar cane fermentation process used in Brazil. Here we report the molecular genetic analysis of a PE-2 derived diploid (JAY270), and the complete genome sequence of a haploid derivative (JAY291). The JAY270 genome is highly heterozygous (~2 SNPs per kilobase), and has several structural polymorphisms between homologous chromosomes. These chromosomal rearrangements are confined to the peripheral regions of the chromosomes, and appear to reflect ectopic homologous recombination between repetitive DNA sequences. Despite the complex karyotype of JAY270, this diploid, when sporulated, had a high frequency of viable spores (~93%). Crosses of haploids derived from JAY270 to a haploid of the unrelated laboratory strain S288c also resulted in diploids that had good spore viability (75-95%). Thus, the rearrangements that exist near the ends of chromosomes do not impair meiosis and spore viability, as they do not span regions that contain essential genes. This observation is consistent with a model in which the peripheral regions of chromosomes represent plastic domains of the genome that are free to recombine ectopically and experiment with alternative structures that may be associated with a fitness benefit. We also explore features of the JAY270 and JAY291 genomes that help explain their high adaptation to industrial environments, exhibiting desirable phenotypes such as high cell mass production and fermentation kinetics, high temperature growth and oxidative stress tolerance. The genomic manipulation of such strains could enable the creation a new generation of industrial organisms, ideally suited for use as delivery vehicles for future bioenergy technologies. This microarray experiment was used to compare the relative gene expression levels between two unrelated S. cerevisiae strain backgrounds: JAY270 and JAY309. Total RNA from each strain was prepared and used to synthesize differentially labeled cDNAs (Cy5 and C3 respectively). A positive Log2 (Red/Green) ratio indicates transcripts more abundant in JAY270, while a negative Log2 (Red/Green) ration indicates transcripts more abundant in JAY309.

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Effect of post-treatment process of microalgal hydrolysate on bioethanol production.

Publications

Effect of post-treatment process of microalgal hydrolysate on bioethanol production.

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