Question

Secondary treatment of the sewage is called biological treatment. Justify this
statement and explain the process.

Answer 1

Hint: Sewage treatment is the process of eliminating waste and contaminants from wastewater of the society, city, colony etc. This wastewater contains mainly household sewage along with some industrial wastewater. In sewage treatment plants various methods are used such as physical, chemical, biological methods to remove contaminants and produce treated wastewater which is safe to release in the environment.

Complete answer:
There are three stages of the sewage treatment process mainly known as primary, secondary, tertiary water treatment.

1. Primary treatment of wastewater involves sedimentation of solid waste within the water. In primary treatment the wastewater is mainly kept in a tank where heavy solid waste matter sinks to the bottom and lighter solid waste matter floats. Once the water is settled, these larger contaminants are filtered out with the help of various techniques and the leftover sludge is fed into a digester, where further processing takes place.

2. Secondary treatment of wastewater works on a deeper level than primary level. It is called as biological treatment because it is designed to substantially degrade the biological content of the waste through aerobic biological processes. This step removes the dissolved organic matter by the use of biological agents. This is done with the help of microbes that can consume organic matter converting it into carbon dioxide, water, and energy for their own growth and reproduction. This can be done in one of three ways discussed below :

Biofiltration: This method of secondary treatment of wastewater employs sand filters, contact filters, or trickling filters that are typically the most effective for small batch wastewater treatment.

Aeration: It is a lengthy process which increases oxygen saturation by introducing air to wastewater, this process can last upto 30 hours.

Oxidation ponds : These are mainly used in warmer places. In addition, this method utilizes natural bodies of water. Wastewater is allowed to pass through such waterbodies for a period of time and is then retained for two to three weeks.

3. Tertiary treatment of wastewater, the third and last step is removal of phosphates and nitrates from water supply. Activated carbon and sand are most commonly used materials that play a major role in this process.


Note: There are many advantages of a sewage wastewater treatment. Such as;
1. Wastewater treatment systems eliminate disease-causing bacteria and kill harmful organisms.
2. These treatment plants can last upto 15 years if maintained correctly and these are very cost effective.
3. The quality of life and the hygienic conditions in the areas with sewage treatment plants have already improved.
4. It works for saving and processing water which is an essential natural resource.