Aerobic decay

Aerobic decay Decay which takes place in the presence of oxygen. 

Apatite apparently forms in vitro at pH values 21s low as 6.8 (possibly as low as 6.4) (Simpson, 1968) and seems to be free from dependence on the oxidation-reduction potential. At Christmas Island (Indian Ocean) a carbonate fluorhydroxyapatite is thought to form through aerobic decay of... 

In some surface waters (and shallow groundwaters) depleted in dissolved oxygen because of their organic-matter content, there is an inverse correlation between the O2 consumed by aerobic decay and respiration and the increase in CO2 found in the water over its equilibrium atmospheric value. This would be expected if changes in the dissolved oxygen and carbon dioxide contents of the water are controlled chiefly by respiration and aerobic decay (reaction 2 ). The ratio of the CO2 produced to the O2 consumed is called the respiratory coefficient, or,... 

Fulvic acid plays a major role in the transport and deposition of Fe, AI, and other metals in soils. The acid is produced by organic decay in the top of the soil s A horizon. Fulvic acid ligands can form soluble complexes with Fe + and AP+ and other metals, which facilitates metal movement downward through the soil. As a rule of thumb, if the molar ratio of metals/fulvic acid is less than 1/1, the metals are water soluble and mobile (Schnitzer 1971). If that ratio exceeds 1/1, the metals become insoluble and immobile. Thus, as fulvic acids are destroyed by aerobic decay or other processes during downward percolation, the metals precipitate, typically in the soil s B horizon. Precipitation of Fe and Al (and also Mn) oxyhydroxides, in turn, leads to coprecipitation and concentration of trace metals such as Cu, Cd, Zn, Co, Ni, and Pb in the soil (cf. Suarez and Langmuir 1975). 

Explain how the CO2 content and pH of natural waters is affected by processes and reactions including the dissolution of C02(g), photosynthesis and respiration, aerobic decay, anaerobic decay (fermentation), nitrate reduction, and denitrification and sulfate reduction. 

The removal of dissolved or particulate organic contaminants is most effective where they can be aerobically broken down. Aerobic decay is most rapid in well-aerated, unsaturated soils and is most complete in thick, unsaturated soils. Organic decay in water-saturated soils tends to be anaerobic, which is much slower and produces more noxious products than aerobic decay (see Chap. 5). Because the O and A horizons of a soil are usually relatively acid (cf. Figs. 7.2 and 7.3), the alkalinity of soils chiefly resides in the clays and carbonates within B and C horizons. Because of their carbonate content, mollisols and aridisols can neutralize acid wastes more rapidly and completely than can oxisols and spodosols, for example. 

The most important CAH compounds (PCE and TCE) can be better diminished anaerobically, starting with the metabohte cis-DCE the aerobe decay is more effective. 

BIOSCREEN (Newell et al., 1996) is an easy-to-use screening model that simulates remediation through natural attenuation (RNA) of dissolved hydrocarbons at petroleum fuel release sites. The software, programmed in a spreadsheet environment and based on the Domenico analytical solute transport model, has the ability to simulate advection, dispersion, adsorption, and aerobic decay as well as anaerobic reactions that have been shown to be the dominant biodegradation processes at many petroleum release sites. 

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