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Biological Treatment
Published in Ralph L. Stephenson, James B. Blackburn, The Industrial Wastewater Systems Handbook, 2018
Ralph L. Stephenson, James B. Blackburn
Respiratory metabolism is the enzyme mediated electron transport from an electron donor to an electron acceptor. Aerobic respiration occurs when molecular Oxygen is used as the electron acceptor, and anaerobic respiration occurs when other molecules are used as electron acceptors.
Microbial biotechnology
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2018
Fermentation is a specific type of heterotrophic metabolism that uses organic carbon instead of oxygen as a terminal electron acceptor. It means that these organisms (bacteria) do not use an electron transport chain to oxidize NADH to NAD+ and therefore must have an alternative method, thus reducing power and maintaining a supply of NAD+ for the proper functioning of normal metabolic pathways (e.g., glycolysis). As oxygen is not required, fermentative organisms are anaerobic. Many organisms can use fermentation under anaerobic conditions and anaerobic respiration when oxygen is not present. These organisms are facultative anaerobes. To avoid the overproduction of NADH, obligately fermentative organisms usually do not have a complete citric acid cycle. Instead of using an adenosine triphosphatase (ATPase) as in respiration, ATP in fermentative organisms is produced by substrate-level phosphorylation, where a phosphate group is transferred from a high-energy organic compound to adenosine diphosphate (ADP) to form ATP. As a result of the need to produce high-energy phosphate-containing organic compounds (generally in the form of CoA esters), fermentative organisms use NADH and other cofactors to produce many different reduced metabolic by-products, often including hydrogen gas (H2) (Figure 5.6). These reduced organic compounds are generally small organic acids and alcohols derived from pyruvate, the end product of glycolysis. Examples include ethanol, acetate, lactate, and butyrate. Fermentative organisms are very important industrially and are used to make many different types of food products. The different metabolic end products produced by each specific bacterial species are responsible for the different tastes and properties of each food.
Microbial Biotechnology
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2020
Fermentation is a specific type of heterotrophic metabolism that uses organic carbon instead of oxygen as a terminal electron acceptor. This means that these organisms do not use an electron transport chain to oxidize NADH to NAD+, and therefore must have an alternative method of reducing and maintaining a supply of NAD+ for the proper functioning of normal metabolic pathways (e.g., glycolysis). As oxygen is not required, fermentative organisms are anaerobic. Many organisms can use fermentation under anaerobic conditions and anaerobic respiration when oxygen is not present. These organisms are facultative anaerobes. To avoid the overproduction of NADH, obligately fermentative organisms usually do not have a complete citric acid cycle. Instead of using an adenosine triphosphatase (ATPase) as in respiration, ATP in fermentative organisms is produced by substrate-level phosphorylation in which a phosphate group is transferred from a high-energy organic compound to adenosine diphosphate (ADP) to form ATP. Because of the need to produce high-energy, phosphate-containing organic compounds (generally in the form of CoA-esters), fermentative organisms use NADH and other cofactors to produce many different reduced metabolic by-products, often including hydrogen gas (H2) (Figure 5.6). These reduced organic compounds are generally small organic acids and alcohols derived from pyruvate, the end product of glycolysis. Examples include ethanol, acetate, lactate, and butyrate. Fermentative organisms are very important industrially and are used to make many different types of food products. The different metabolic end products produced by each specific bacterial species are responsible for the different tastes and properties of each food.
The response of C/N/S cycling functional microbial communities to redox conditions in shallow aquifers using in-situ sediment as bio-trap matrix
Published in Environmental Technology, 2023
Cui Li, Rong Chen, Weiwei Ouyang, Chen Xue, Minghui Liu, Hui Liu
Anaerobic respiration is essential in reducing contaminants, nitrate, and sulphate [5, 10, 11], which requires a reductive environment and sufficient electron donors [10]. Aerobic processes such as oxidative degradation of contaminants, aerobic denitrification, and sulfur oxidation require the participation of aerobic bacteria, which need oxygen [7–9]. In the actual aquifer, the restricted electron donors and acceptors often limit the C, N, and S cycling and pollutants detoxification. Therefore, stimulated measures to provide more electron donors and acceptors, such as adding H2-producing substances or injecting air, pure O2, ozone, or H2O2 to provide O2, have emerged as practical and sustainable approaches for cleaning-up contaminated sites [12], which will change redox conditions. For example, Cai et al. (2015) found that aeration could significantly promote the degradation of petroleum hydrocarbons [13]. Khanitchaidecha et al. (2012) facilitated the removal of NO3-N under a low rate of H2 supply (30–70 mL/min) [14]. Recently, it has been reported that H2 can be directly supplied by electrolysis to promote the anaerobic degradation of chlorinated hydrocarbons [15–17]. The variation of redox conditions is supposed to alter the microbial community, thus interfering with the biogeochemical cycling of many elements such as C, N, and S in the groundwater system [18]. However, it is need to clarify how the microbial composition and functions on the C/N/S-cyclings response to different ORP values caused by H2 and O2 supplies.