*4.4.1. Aerobic treatment*

**3.** BOD is efficiently treated in the range of 60 to 500 mg L-1. Wastewaters in excess of 500 mg L-1 BODs have been treated successfully if sufficient dilution is applied in the treatment

**4.** The biological treatment is effective in removing up to 95% of the BOD. Large tanks are

**5.** The biological treatment systems are unable to handle "shock loads" efficiently. Equali‐ zation is necessary if the variation in strength of the wastewater is more than 150% or if

**6.** The carbon:nitrogen:phosphorus (C:N:P) ratio of wastewater is usually ideal. The C:N:P ratio of industrial wastewaters should range from 100:20:1 to 100:5:1 for a most advanta‐

**7.** If the C:N:P ratio of the wastewater is strong in an element in comparison to the other elements, then poor treatment will result. This is especially true if the wastewater is very strong in carbon. The wastewater should also be neither very weak nor very strong in an

**8.** Oils and solids cannot be handled in a biological treatment system because they negatively affect the treatment process. These wastes should be pretreated to remove solids and oils.

**9.** Toxic and biological-resistant materials require special consideration and may require

**10.** Although the capacity of the wastewater to utilize oxygen is unlimited, the capacity of

pretreatment before being introduced into a biological treatment system.

process, or if an anaerobic process was implemented as a pretreatment process.

required in order to eliminate the entire BOD, which is not feasible.

element; although very weak is acceptable, it is difficult to treat.

any aeration system is limited in terms of oxygen transfer.

geous biological process.

**Figure 4.** Microbial growth curves [1].

8 Wastewater Treatment Engineering

that wastewater at its peak concentration is in excess of 1,000 mg L-1 BOD.

Aeration has been used to remove trace organic volatile compounds (VOCs) in water. It has also been employed to transfer a substance, such as oxygen, from air or a gas phase into water in a process called "gas adsorption" or "oxidation", i.e., to oxidize iron and/or manganese. Aeration also provides the escape of dissolved gases, such as CO2 and H2S. Air stripping has been also utilized effectively to remove NH3 from wastewater and to remove volatile tastes and other such substances in water [2]. Samer [4] and Samer et al. [5] mentioned that aerobic treatment with biowastes is effective in reducing harmful gaseous emissions as greenhouse gases (CH4 and N2O) and ammonia.
