Methane aerobic degradation

Soil. p,//-DDD and p./Z-DDE are the major metabolites of /5,//-DDT in the environment (Metcalf 1973). In soils under anaerobic conditions, /5,//-DDT is rapidly converted to p,//-DDD via reductive dechlorination (Johnsen, 1976) and very slowly to p,//-DDE under aerobic conditions (Guenzi and Beard, 1967 Kearney and Kaufman, 1976). The aerobic degradation of p,pD yY under flooded conditions is very slow with p,//-DDE forming as the major metabolite. Dicofol was also detected in minor amounts (Lichtenstein et al., 1971). In addition to p./Z-DDD and /5,//-DDE, 2,2-bis(/5-chlorophenyl)acetic acid (DDA), bis(jo-chlorophenyl)methane (DDM), /5,/y dichlorobenzhydrol (DBH), DBF, and p-chlorophenylacetic acid (PCPA) were also reported as metabolites of /5,//-DDT in soil under aerobic conditions (Subba-Rao and Alexander, 1980). 

Rates of methane production via both acetate fermentation and C02 reduction were directly measured with radiotracer techniques in the sulfate-depleted sediments of Saanich and Princess Louisa Inlets (Kuivila etal., 1990). Comparison of measured and modeled rates suggests that these two pathways account for the majority of methane produced below the sulfate reduction zone in the sediments of both the basins. Prior aerobic degradation of the organic matter has little influence on the pathways of methane production. 

In some cases, microorganisms can transform a contaminant, but they are not able to use this compound as a source of energy or carbon. This biotransformation is often called co-metabolism. In co-metabolism, the transformation of the compound is an incidental reaction catalyzed by enzymes, which are involved in the normal microbial metabolism.33 A well-known example of co-metabolism is the degradation of (TCE) by methanotrophic bacteria, a group of bacteria that use methane as their source of carbon and energy. When metabolizing methane, methanotrophs produce the enzyme methane monooxygenase, which catalyzes the oxidation of TCE and other chlorinated aliphatics under aerobic conditions.34 In addition to methane, toluene and phenol have been used as primary substrates to stimulate the aerobic co-metabolism of chlorinated solvents. 

Degradation of solid waste materials in a landfill proceeds from aerobic to anaerobic decomposition very quickly, thereby generating gases that collect beneath the closure FML. Almost 98% of the gas produced is either carbon dioxide (CO2) or methane (CH4). Because C02 is heavier than air, it will move downward and be removed with the leachate. However, CH4, representing about 50% of the generated gas, is lighter than air and, therefore, will move upward and collect at the bottom of the facility s impermeable FML. If the gas is not removed, it will produce a buildup of pressure on the LML from beneath. 

Azo dye metabolites Activated sludge Under aerobic conditions, two compounds 4,4 -thiodianiline and p-kresidine were most easily degraded, followed by 4,4 -diaminodiphenylmethane and 2-naphthylamine. Under anaerobic conditions, stabilities of the amines were totally different and compounds p-kresidine, 4,4 -diaminodiphenyl methane, and 2-naphthylamine were degraded while the 4-chloroaniline, 2,4-diaminotoluene, and 2,4-diaminoanisole were partly degraded [16]... 

While 02 serves as the electron acceptor in aerobic biodegradation processes forming H20 as the final product, degradation in anaerobic systems depends on alternative electron acceptors such as sulfate, nitrate or carbonate, which yield, ultimately, hydrogen sulfide (H2S), molecular nitrogen (N2) and/or ammonia (NH3) and methane (CH4), respectively. 

TCE is the other major contaminant at the site and is a common groundwater contaminant in aquifers throughout the United States [425]. Since TCE is a suspected carcinogen, the fate and transport of TCE in the environment and its microbial degradation have been extensively studied [25,63, 95,268,426,427]. Reductive dechlorination under anaerobic conditions and aerobic co-metabolic processes are the predominant pathways for TCE transformation. In aerobic co-metabolic processes, oxidation of TCE is catalyzed by the enzymes induced and expressed for the initial oxidation of the growth substrates [25, 63, 268, 426]. Several growth substrates such as methane, propane, butane, phenol, and toluene have been shown to induce oxygenase enzymes which co-metabolize TCE [428]. 

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