Essential Features of Biological Treatment Systems
All biotechnology treatments have certain central similarities, irrespective of the specific details of the technique. The majority of applications make use of indigenous, resident microbes, though in some cases the addition of specialised organisms may be warranted. Thus, the functional biology may be described as a process of bioenhancement or bioaugmentation, or occasionally a mixture of both.
Bioenhancement concentrates solely on the existing microfauna, stimulating their activity by the manipulation of local environmental conditions. Bioaugmen-tation, by contrast, requires the deliberate introduction of selected microbes to bring about the required clean-up. These additions may be unmodified ‘wild-type’ organisms, a culture selectively acclimatised to the particular conditions to be encountered, or genetically engineered to suit the requirements. Enzyme or other living system extracts may also be used to further facilitate their activity. Some land remediation methods simultaneously bioenhance resident bacteria and bioaugment the process with the addition of fungi to the soil under treatment.
In the final analysis, all biological approaches are expressly designed to opti-mise the activities of the various micro-organisms (either native to the particular soil or artificially introduced) to bring about the desired remediation. This gener-ally means letting them do what they would naturally do but enhancing their per-formance to achieve it more rapidly and/or more efficiently. Effectively it is little different from accelerated natural attenuation and typically involves management of aeration, nutrients and soil moisture, by means of their addition, manipula-tion or monitoring, dependent on circumstance. However simple this appears, the practical implications should not be underestimated and careful understand-ing of many interrelated factors is essential to achieve this goal. For example, successful aerobic biodegradation requires an oxygen level of at least 2 mg/litre; by contrast, when the major bioremediation mechanism is anaerobic, the presence of any oxygen can be toxic. The presence of certain organic chemicals, heavy metals or cyanides may inhibit biological activity; conversely, under certain cir-cumstances microbial action may itself give rise to undesirable side effects like iron precipitation, or the increased mobilisation of heavy metals within the soil.
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