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Waste to Bioenergy: A Sustainable Approach
Published in Jos T. Puthur, Om Parkash Dhankher, Bioenergy Crops, 2022
Monika Yadav, Gurudatta Singh, Jayant Karwadiya, Akshaya Prakash Chengatt, Delse Parekkattil Sebastian, R.N. Jadeja
Alcoholic fermentation is a biotechnological process accomplished by yeast, some kinds of bacteria, or a few other microorganisms to convert sugars into ethyl alcohol and carbon dioxide. In this fermentation process, yeast is mostly used as a bio-culture and aqueous solution of monosaccharide (raw materials) as the culture media for the production of beverages. In the alcoholic fermentation process, yeast generally carries out the aerobic fermentation process, but it may also ferment the raw materials under anaerobic conditions. In the absence of oxygen, alcoholic fermentation occurs in the cytosol of yeast (Sablayrolles 2009, Stanbury et al. 2013). Alcoholic fermentation begins with the breakdown of sugars by yeasts to form pyruvate molecules, which is also known as glycolysis. Glycolysis of a glucose molecule produces two molecules of pyruvic acid. The two molecules of pyruvic acid are then reduced to two molecules of ethanol and 2CO2 (Huang et al. 2015). Bioethanol is used as a bioenergy sources for transportation and other uses.
Microbial Metabolism
Published in Maria Csuros, Csaba Csuros, Klara Ver, Microbiological Examination of Water and Wastewater, 2018
Maria Csuros, Csaba Csuros, Klara Ver
During aerobic respiration, glycolysis is followed by the Krebs cycle and the electron transport system. The Krebs cycle is the oxidation of a derivative of pyruvic acid: acetyl co-enzyme A to CO2 with the production of some adenosine triphosphate (ATP), nicotineamide-adenine-dinucleotide (NAD) reduced form (NADH) and another reduced electron carrier, flavin–adenine–dinucleotide reduced form (FADH2).
Applications in Biology
Published in Gabriel A. Wainer, Discrete-Event Modeling and Simulation, 2017
The chief function of the mitochondria is to create energy for cellular activity by the process of aerobic respiration. In this process, glucose is broken down in the cell’s cytoplasm, via the glycolysis process, to form pyruvic acid. In a series of reactions, part of which is called the Krebs cycle, the pyruvic acid reacts with water to produce carbon dioxide and hydrogen. Energy is released as the electrons flow from the coenzymes down the electron transport chain to the oxygen atoms. The enzyme ATPase, which is embedded in the inner membrane, adds a phosphate group to adenosine diphosphate (ADP) in the matrix to form ATP. Aerobic respiration is an ongoing process, and mitochondria can produce hundreds of thousands of ATP molecules per minute. ATP is transported to the cytoplasm, where it is used for virtually all energy-requiring reactions. As ATP is used, it is converted into ADP, which is returned by the cell to the mitochondrion and is used to build more ATP [19]. Specific enzymes control each of the different reactions, as shown in Figure 8.32.
Utilization of vetiver grass containing metals as lignocellulosic raw materials for bioethanol production
Published in Biofuels, 2021
Elvi Restiawaty, Arinta Dewi, Yogi Wibisono Budhi
Two-stage fermentation – that is, a combination of micro-aerobic and anaerobic fermentation – could enhance bioethanol production. As shown in the data labeled ‘A’ in Figure 5, the bioethanol yield using the two-stage fermentation (77%) was higher than that using the one-stage fermentation (52%). A similar result was reported by Saisaard et al. (2011), where the bioethanol production obtained under the two-stage fermentation was higher than that only using a micro-aerobic or anaerobic process [28]. About 72.6% of bioethanol was yielded from the two-stage process, whereas 61.3% ethanol was yielded under the micro-aerobic process [28]. The catabolism of 1 mole of glucose through glycolysis produces 2 moles of ATP, 2 moles of NADH, and 2 moles of pyruvic acid. Under aerobic conditions, pyruvate is used to generate energy for cell growth or anabolism through the tricarboxylic acid cycle (TCA). However, if the substrate concentration is high, then the metabolism is overflowing, so pyruvate will be directed to the fermentation path rather than the TCA cycle. Under anaerobic conditions, pyruvate will decarboxylate to acetaldehyde, which is the last electron receiver to produce bioethanol.
Effects of mixotrophic cultivation on antioxidation and lipid accumulation of Chlorella vulgaris in wastewater treatment
Published in International Journal of Phytoremediation, 2020
Ran Li, Jie Pan, Minmin Yan, Jiang Yang, Wenlong Qin
The fatty acid synthesis pathway of mixotrophic C. vulgaris in wastewater is illustrated in Figure 5. Specifically, CO2 enters the chloroplast to produce glyceraldehyde triphosphate through the Calvin cycle. After that, the glycolytic pathway forms pyruvate, which releases a CO2 molecule and produces acetyl-CoA under the action of pyruvate dehydrogenase (PDH) (Avidan et al.2015). The first key reaction in fatty acid synthesis is the acetyl-CoA conversion to malonyl-CoA catalyzed by ACCase. Our results showed the ACCase activity was enhanced and contributed to the fatty acid accumulation of C. vulgaris cultured in wastewater. During heterotrophic metabolism, after a small molecule of organic matter (e.g., glucose) enters the cell, it is first converted to pyruvic acid by the glycolysis pathway and then by the fatty acid metabolism pathway (Gao et al.2014). Glucose can also be converted into ADPGlc and then into starch under the catalysis by AGPase. However, the activity of ACCase in mixotrophic C. vulgaris in wastewater was weakened, indicating more glucose molecules participate in fatty acid synthesis, causing lipid accumulation.
Biovalorization of glucose in four culture media and effect of the nitrogen source on fermentative alcohols production by Escherichia coli
Published in Environmental Technology, 2020
David Fernández-Gutierrez, Marc Veillette, Antonio Ávalos Ramirez, Anne Giroir-Fendler, Nathalie Faucheux, Michèle Heitz
Both, 2,3-BD and A can be produced by a chemical transformation. The diol 2,3-BD can be obtained performing the hydrolysis of butene oxide at a pressure of 50 bar and a temperature varying from 160°C to 220°C, with a residence time unspecified [12]; while 2-butanone can be transformed into A using, for instance, a palladium based catalyst in a concentration up to 3.3 mmol/L in water-THF (50:50, v/v) at 25°C and 1 atm, residence time unspecified [13]. However, the biological processes are usually selected because of environmental concerns about the reduction of fossil fuels consumption, improvements of green production technologies like fermentation, and soft operating conditions of those process (generally operating in a temperature range between 25°C and 45°C, at atmospheric pressure and around neutral pH) [7,14]. ABD can be produced by a biological transformation of saccharides like glucose by yeast (i.e. Saccharomyces cerevisiae) or bacteria (i.e. Enterobacter cloacae, Klebsiella oxytoca or Serratia marcescens) [7,8]. The mentioned bacteria naturally produce ABD. However, they possess a biosafety level 2, which means they are human pathogenic [15]. Other bacteria (e.g. Escherichia coli) can be genetically modified to host the genes of metabolic pathways to produce ABD [7,16]. It is interesting to create genetically modified bacteria able to produce ABD because the genetic modification of bacteria can help: (i) to eliminate the metabolic pathway of other sub products like acetic acid in order to improve the production of ABD; and (ii) to use bacteria like E. coli K12 which possess a biological safety level 1 (non-human pathogenic) but do not have the metabolic pathway to produce ABD [10,17]. In the metabolic pathways involved in ABD synthesis, glucose is first transformed into pyruvic acid (PA) (glycolysis). Then, the transformation of PA into 2,3-BD is performed by 3 enzymes: α-acetolactate synthase (ALS), α-acetolactate decarboxylase (ALDC) and 2,3-butanediol dehydrogenase (BDH) [7]. The enzyme ALS catalyzes the formation of α-acetolactate from PA. Following this step, ALDC transforms α-acetolactate into A, a 2,3-BD precursor [18]. Finally, the enzyme BDH converts A into 2,3-BD [19].