Microbiology is the study of small (microscopic) organisms which are too small to be viewed with unaided eyes and could be plants, animals or inanimate objects. It is through such studies that microscopic bacteria, protozoa, viruses, fungi etc. were discovered and their behavioral characteristics known.
In the field of microbiology, many branches of it exist, thus we have things like: environmental microbiology, microbiological ecology, applied microbiology and microbial biotechnology. All these relate and differ slightly at different times and occasions.
Whereas microbial ecology is the study of the interaction of micro-organisms within the environment, environmental microbiology is an applied field where the study of micro-organisms in the environment leading to the benefit of the society is emphasized.
It is a subset of applied microbiology and interfaces with water, waste-water, air, soil, food, industrial microbiology and others. Microbial biotechnology encompasses the field which includes the manipulation of the microbes to increase their practical benefit wherein the principles of applied microbiology are applied.
The new focus of environment as a whole has led to the development of new activities related to the application of principles of water, waste- water and air microbiology which forms the scope of environmental biotechnology.
This part addresses various aspects of waste-water treatment since generally it is now suitably treated before dumping into the rivers/streams so as to reduce the threat of waterborne diseases.
The fate of the discharged waste is determined by the self-purification potential of the receiving water body.
Self-purification is based on biogeochemical cycling activities and inter-population relationships of the indigenous (autochthonous) microbial populations. Organic nutrients are mineralized by the heterotrophic aquatic organisms.
Ammonia is nitrified and inorganic nutrients are utilized by higher aquatic plants. Non-indigenous (alochthonous) population of enteric pathogens that enter through waste is eliminated by competition and predation of the autochthonous microorganisms.
The waste-water may overwhelm the self-purification capacity of the aquatic system causing pollution of receiving water. Depending on the climatic and environmental factors the water may attain an acceptable quality level in the stream, downstream from the sewage outfall.
A well-defined profile of pollution and self- purification of the receiving water is obtained by a succession of changes in water quality that occurs on the downstream of the point source of pollution as seen in the figure below.
Self-purification is a slow process and a heavily polluted stream may have to traverse quite a long distance for days to get purified. Whenever the waste-water is discharged, the suspended matter either settles at the bed near the point of discharge or gets carried away.
The organic matter is utilized by the aerobic micro-organisms reducing the dissolved oxygen. As the organic matter is depleted, the number of micro-organisms is also reduced. The re-aeration rate of the atmosphere catches up.
The water becomes clear and the stream returns to the original condition and the self-purification is accomplished. The Biochemical Oxygen Demand (BOD) and the Dissolved Oxygen (DO) of the receiving waters are parameters that give good measure of pollution that exists in the receiving stream.
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