**4.2. Bacterial kinetics**

The bacterial kinetics can be shown in Figures 3 and 4. The microbial growth curve that shows bacterial density and specific growth rate at the different growth phases is shown in Figure 3. The microbial growth curves that compare the total biomass and the variable biomass are shown in Figure 4.

**Figure 3.** Microbial growth curve [1].

Where, *μ* is the specific growth rate coefficient; *λ* is the maximum growth rate coefficient that occurs at 0.5 *μ*max; *S* is the concentration of limiting nutrient, that is BOD and COD; and *KS* is

Generally, the bacterial growth can be explained by the following simplified figure:

Organics+Bacteria+Nutrients+Oxygen

2 2

Several bioenvironmental factors affect the activity of bacteria and the rate of biochemical reactions. The most important factors are: temperature, pH, dissolved oxygen, nutrient concentration, and toxic materials. All these factors can be controlled within a biological treatment system and/or a bioreactor in order to ensure that the microbial growth is maintained under optimum bioenvironmental conditions. The majority of biological treatment systems operate in the mesophilic temperature range, where the optimal temperature ranges from 20°C to 40°C. Aeration tanks and percolating filters operate at the temperature of the wastewater that ranges from 12°C to 25°C; although in percolating filters, the air temperature and the ventilation rate may have a significant effect on heat loss. The higher temperatures increase the biological activity and metabolism, which result in increasing the substrate removal rate.

® New Bacteria+CO +H O+ResidualOrganics+Inorganics

the Monod coefficient [3].

6 Wastewater Treatment Engineering

**Figure 2.** Photosynthesis and oxidation [2].
