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Basics of Earth Science
Published in Takashiro Akitsu, Environmental Science, 2018
Carbon is ingested and/or converted into heterotrophic organisms in the biosphere. It also includes decomposition of living organisms and waste products, such as fermentation and decay by fungi and bacteria. Carbon emitted from the biosphere is mostly caused by respiration. In the environment where oxygen exists, carbon dioxide is released into the surrounding atmosphere and water by the action of aerobic respiration. On the other hand, in anaerobic respiration, methane is released to the surrounding environment (atmosphere or hydrosphere). Some of them may remain as carbon in the biosphere without decomposing them as bodies (some peat-like), but others move to the geosphere. Particularly animal shells (corals, shells, etc.) made of calcium carbonate go through limestone after deposition process.
Superficial deposits
Published in A.C. McLean, C. D. Gribble, Geology for Civil Engineers, 2017
Organic matter in soils is broken down by micro-organisms to give water and either carbon dioxide or methane and small quantities of ammonia and nitric acid. Carbon dioxide is produced by aerobic micro-organisms, which require oxygen to survive. Methane is produced by anaerobic micro-organisms which flourish in environments that are deficient in oxygen, referred to as reducing environments. Decay and decomposition take place much more quickly where oxygen is present. An excessive accumulation of decaying organic matter will consume all the available oxygen and produce a reducing environment, for example in a poorly drained area such as a bog or in lakes where circulation is poor. In these circumstances sulphides form and pyrite is usually present.
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.
Municipal solid waste management and greenhouse gas emission control through an inexact optimization model under interval and random uncertainties
Published in Engineering Optimization, 2018
Jie Wu, Chi Ma, DeZheng Zhang, Ye Xu
With rapid urbanization and expanding population growth, the magnitude of municipal solid waste (MSW) has increased dramatically, causing many problems for local managers. For example, the limited treatment capacities of existing facilities are incapable of meeting the treatment requirements owing to increasing waste generation rates, and the design and implementation of current waste management strategies are inefficient. These challenges have triggered serious environmental pollution issues. Currently, landfill, incineration and composting are three frequently used treatment technologies. The anaerobic treatment of organic matter produces methane (CH4) and the incineration process generates carbon dioxide (CO2). It is recognized that waste treatment is a major emission source of greenhouse gases (GHGs) (Friedrich and Trois 2013; Chen and Lo 2016). A large amount of GHGs will cause global warming, leading to the frequent occurrence of natural disasters (Chen et al. 2017). Consequently, effective waste management with consideration of GHG emission control is desired.
Environmental impact of biogas: A short review of current knowledge
Published in Journal of Environmental Science and Health, Part A, 2018
Valerio Paolini, Francesco Petracchini, Marco Segreto, Laura Tomassetti, Nour Naja, Angelo Cecinato
A main objective of biogas industry is the reduction of fossil fuel consumption, with the final goal of mitigating global warming. However, anaerobic digestion is associated to the production of several greenhouse gases, namely carbon dioxide, methane and nitrous oxide. As a consequence, dedicated measures should be taken in order to reduce these emissions. According to Hijazi,[19] the main measures to improve the global warming reduction potential of biogas plants are: to use a flare avoiding methane discharge, to cover tanks, to enhance the efficiency of combined heat and power (CHP) units, to improve the electric power utilisation strategy, to exploit as much thermal energy as possible, to avoid leakages. Similar conclusions were obtained by Buratti and co-workers[20] for the specific case study of cereal crops in Umbria, Italy. Biomethane chain exceeds the minimum value of GHG saving (35%) mainly due to the open storage of digestate; usual practices to improve GHG reduction (up to 68.9%) include using heat and electricity produced by the biogas CHP plant, and covering digestate storage tanks.
Development of a low-cost electrochemical sensor for monitoring components in wastewater treatment processes
Published in Environmental Technology, 2022
Rafael Frederico Fonseca, Marcelo Zaiat
Anaerobic digestion is a biological process that occurs in the absence of oxygen and is widely used for organic matter decomposition and stabilisation. Due to the presence of several groups of microorganisms and given their metabolic intricacies so that the organic matter can be degraded, any imbalance in these routes can lead to instability, or even to failure, which could lead to economic losses in the case of industrial plants [1]. The most common causes of process instabilities are organic overload, ammonia inhibition, over-acidification, and long-chain fatty acid inhibition [2]. Wu et al. [1] pointed out that proper monitoring of the process and a good understanding of its mechanisms are key steps to help increase stability and performance.