Chemical Competition

bial populations, maintained under environmental conditions conducive to their metabolic activity are an important means of biological transformation or degrading these otherwise refractory wastes.

All microorganisms require adequate levels of inorganic and organic nutrients, growth factors (vitamins, magnesium, copper, manganese, sulfur, potassium, etc.), water, oxygen, carbon dioxide and sufficient biological space for survival and growth. One or more of these factors is usually in limited supply. In addition, various microbial competitors adversely affect each other in struggling for these limited resources. Other factors influencing microbial degradation rates include microbial inhibition by chemicals in the waste to be treated, the number and physiological state of the organisms as a function of available nutrients, the seasonal state of microbial development, predators, pH, and temperature. Interaction between these and other potential factors can cause wide variations in degradation kinetics.

For these and other reasons, aerobic biodegradation is usually carried out in processes where many of the requisite conditions can be controlled. Such processes include conventional activated-sludge processes, with modifications such as sequencing batch reactors, and aerobic-attached growth biological processes such as rotating biological contactors and trickling filters. Recently developed genetically engineered bacteria are reported to be effective for biological treatment of specific, relatively uniform, hazardous wastes.

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