Organic compounds anaerobic conditions

Table CXXVIll Bioaugmentation using LLMO C l In an anaerobic condition Organic compound Resorcinol...

Table CXXXII Bloaugmentatlon using LLMO C 1 in an anaerobic condition Organic compound Salicylic acid...

Aerobic, Anaerobic, and Combined Systems. The vast majority of in situ bioremediations ate conducted under aerobic conditions because most organics can be degraded aerobically and more rapidly than under anaerobic conditions. Some synthetic chemicals are highly resistant to aerobic biodegradation, such as highly oxidized, chlorinated hydrocarbons and polynuclear aromatic hydrocarbons (PAHs). Examples of such compounds are tetrachloroethylene, TCE, benzo(a)pyrene [50-32-8] PCBs, and pesticides. 

Hydrogen sulphide This is produced by the putrefaction of organic sulphur compounds or by the action of sulphate-reducing bacteria in anaerobic conditions (e.g. in polluted river estuaries). It is fairly rapidly oxidised to SOj and concentrations are considerably lower than those of (Table 2.6). Nevertheless it is responsible for the tarnishing of copper and silver at normal atmospheric concentrations. 

Biodegradation. Under aerobic conditions, biodegradation results in the mineralization of an organic compound to carbon dioxide and water and—if the compound contains nitrogen, sulfur, phosphorus, or chlorine—with the release of ammonium (or nitrite), sulfate, phosphate, or chloride. These inorganic products may then enter well-established geochemical cycles. Under anaerobic conditions, methane may be formed in addition to carbon dioxide, and sulfate may be reduced to sulhde. 

In contrast, cells grown anaerobically with nitrate and vanillate were able to oxidize vanillate under both aerobic and anaerobic conditions. The cells were also able to demethylate a much wider spectrum of aromatic methoxy compounds under anaerobic conditions than under aerobic conditions (Taylor 1983). Such subtleties should be clearly appreciated and taken into consideration in evaluating the degradative potential of comparable organisms under different physiological conditions. 

The most broadly studied organic nitrogen compound is probably quinoline however, most studies report biodegradation. As we have seen from Table 14, quinoline is representative of the organonitrogen compounds present in the diesel cut. Its transformation has been studied in both, anaerobic and aerobic conditions. Several metabolic pathways have been proposed to explain the aerobic transformations however, no pathway has been proposed for quinoline metabolism under anaerobic conditions. 

Another process for converting organic ring compounds was disclosed for producing value-adding products from fossil fuel, under anaerobic conditions [442], The process is employed at subsurface level, at a depth of at least 500 ft below ground surface. The... 

From the biological point of view, the effect of anaerobiosis has been characterized in purely anaerobic, facultative anaerobic, and aerobic bacteria, in yeasts, and in tissues from higher organisms [6-12], From these studies it can be deduced that almost every azo compound can be biologically reduced under anaerobic conditions [4]. Reduced flavins are produced by cytosol flavin-dependent reductases [6, 13], while quinone reductase activity located in the plasma membrane [14] and extracellular azo reductase activities [9, 15] were also observed. 

These energy-producing reactions are termed respiration processes. They require the presence of an external compound that can serve as the terminal electron acceptor of the electron transport chain. However, under anaerobic conditions, fermentation processes that do not require the participation of an external electron acceptor can also proceed. In this case, the organic substrate undergoes a balanced series of oxidative and reductive reactions, i.e., organic matter reduced in one step of the process is oxidized in another. 

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