In biological treatment, the organic or hydrocarbon food serves as an energy source to the bacteria.
Aerobic processes use oxygen, anoxic processes use oxygen nitrite and nitrate, and
anaerobic processes use sulfate or carbon dioxide as electron acceptors. In the process of metabolism,the nutrients in solution in the form of hydrocarbons, nitrogen, phosphorous and metallic micronutrients, through osmosis, catalyzed by enzymes, pass through the bacterial cell membrane and are converted into useful energy.
A bacteria uses enzymes to gather and retrieve food in the form of hydrocarbons. In the process of converting these hydrocarbons to food for the bacteria, enzymes break the hydrocarbons down aerobically (in the presence of free oxygen) into carbon dioxide (CO2) and water (H2O),
A bacterium, whether aerobic anoxic or anaerobic, requires a certain environment to grow. Upon growth, the bacterium reproduces by splitting at a logarithmic rate.
The enzyme catalyzation rate is affected by temperature, pH and substrate concentration.
Temperature affects enzyme activation generally in accordance with Fig. B, although each enzyme displays maximum activity at some specific temperature. Likewise, each enzyme displays maximum activity at a certain pH range generally in accordance with Fig. B
Why Bacteria Die?
In accordance with these requirements,
An acceptable environment is required for growth, which includes an acceptable temperature and pH and an absence of toxic chemicals. In the absence of any of these requirements or in the presence of any toxic chemicals, a bacterial cell will eventually die.
In the presence of these requirements and absent toxicity, a bacterial cell has a growth and death rate represented by a classic bell shaped curve as represented in Fig. C
During the initial growth phase. the bacteria split and logarithmically increase until one or more of the environmental factors is depleted. If there is no depletion, the growth phase will continue.Beginning with a given amount of food, bacterial growth will eventually reach a stationary phase upon depletion of food, followed by a death phase and finally, endogenous respiration or cannibalism.During endogenous respiration, the bacteria feed on each other in the absence of available food.As endogenous respiration declines, the remaining non-biodegradable residue (NBDR), remains solid particles settle.