Pre-treatment units

- Pre-treatment units are designed to remove or reduce certain pollutants and debris from wastewater before it enters the main treatment process.
- These units help in protecting downstream treatment processes and equipment from damage and excessive wear and tear.
- Some common pre-treatment units include bar screens, grit chambers, flow equalization tanks, and pH adjustment tanks.

a) Bar screen and grit chamber

- Bar screens are used to remove large solid objects like sticks, rags, and debris from wastewater.
- These objects can clog pipes, damage pumps, and hinder the treatment process.
- Grit chambers, on the other hand, are used to remove heavy inorganic particles like sand, gravel, and grit from wastewater.
- These particles can cause abrasion and damage to pumps, pipes, and other equipment if not removed.

b) Flow equalization and proportion tank

- Flow equalization tanks are used to balance the flow rate and volume of wastewater entering the treatment plant.
- They help in reducing the peak flow rates and variations, which can overload the treatment process.
- Proportion tanks are used to store and mix chemicals or additives with wastewater for pH adjustment or other treatment purposes.
- They ensure that the chemicals are properly mixed and distributed in the wastewater for effective treatment.

c) Neutralization for pH adjustment tank

- Neutralization tanks are used to adjust the pH level of wastewater before it enters the main treatment process.
- Some industrial wastewater streams may be highly acidic or alkaline, and adjusting the pH is necessary for effective treatment.
- Neutralization tanks typically use chemicals like acids or alkalis to bring the pH within the desired range for treatment.

d) Nutrient removal tank

- Nutrient removal tanks are not typically considered pre-treatment units.
- They are part of the secondary or tertiary treatment process, where specific nutrients like nitrogen and phosphorus are removed from wastewater.
- Nutrient removal is often achieved through biological or chemical processes, such as denitrification or phosphorus precipitation.
- These tanks are designed to promote the growth of specific microorganisms or facilitate chemical reactions that remove the targeted nutrients.

Therefore, option 'D' (Nutrient removal tank) is not a pre-treatment unit as it is part of the secondary or tertiary treatment process, rather than the initial pre-treatment stage.