Processes During Oxygen Consumption

Processes During Oxygen Consumption

	Processes During Oxygen Consumption The microorganisms which directly assimilate the waste organic matter may be called as primary heterotrophs. While growth is occurring, some of the organic compounds are used to synthesise compounds which are stored in the microbial cells as a food reserve. Assimilation is considered to be the first step of BOD exertion, and when most of the organic compounds have either been oxidised or converted into new microorganisms or stored food reserves, it has been completed.
The assimilation phase is followed by a period of endogenous metabolism which is manifest by oxygen consumed as the primary heterotrophs metabolise their stored food reserve. Endogenous metabolism is a mechanism by which the microbial cells meet their maintenance requirements, i.e. replace protein molecules and other cellular components which break down spontaneously. As some of the primary heterotrophs die, the cell membranes rupture and the cell contents spill out. This organic material supports the growth of secondary heterotrophs. This growth which takes place when there is an overall decrease in the total number of viable cells present is called cryptic growth. Secondary heterotrophs also include slowly growing bacteria or fungi which are able to assimilate waste organic compounds which are not utilised by the primary heterotrophs.
In addition, protozoa and microscopic invertebrates which feed on the bacteria and fungi are also present in the waste waters. Oxygen consumption by the predators occurs while the heterotrophs are growing as well as when they are in the endogenous phase but this type of oxygen consumption is quantitatively much more significant during the endogenous phase.
Waste water contains ammonia and proteinaceous material which will release ammonia when assimilated. Ammonia serves as an energy source for nitrifying bacteria. Nitrification is an oxygen demand which is independent of the organic content of the waste water of effluents and interferes with the actual oxygen consumed by the microorganisms. Reduction of the nitrogen from the effluent is an important part of the effectiveness of waste water treatment in preventing water pollution. If biological waste water treatment processes are exposed to sunlight they will often grow significant amounts of algae. This is more common for attached growth processes (trickling filters). Any algal cell incorporated into a BOD sample will, when incubated in the dark, consume rather than produce oxygen, and this oxygen consumption is measured as part of the BOD, but the algal presence is not related to waste organic matter originally present in the waste water and is not proportional to the ultimate carbonaceous oxygen demand of the effluent.
	BOD bottles are used for testing the concentration of oxygen in a waste sample more so the amount of residual oxygen which directly relates to the presence of organic matter and microbial load in the water sample. BOD bottles are either made of glass or plastic. The important characteristics of a BOD bottle are it serves as a culture vessel for the waste water microorganisms and it can be filled completely with a dilute sample and then sealed from contact with the atmosphere.

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