Question

List examples of major unit operations in preliminary, primary, secondary and tertiary treatment stages. What is the main objective of each treatment stage?

Answer 1

Primary treatment

objective - to remove large contaminants from the water

Primary treatment of wastewater includes sedimentation of solid waste within the water. This is done after filtering out larger contaminants within the water. Wastewater is passed through several tanks and filters that separate water from contaminants. The resulting “sludge” is then fed into a digester, in which further processing takes place. This primary batch of sludge contains nearly 50% of suspended solids within wastewater.

Secondary Wastewater Treatment

objective - to remove smell , organics from the water

Biofiltration

This method of secondary treatment of wastewater employs sand filters, contact filters, or trickling filters to ensure that additional sediment is removed from wastewater.

Aeration

Aeration is a long, but effective process that entails mixing wastewater with a solution of microorganisms.

Tertiary Wastewater Treatment

objective - to remove the nitrogen and phosphorous and nitrogen compounds from WATER

This third and last step in the basic wastewater management system is mostly comprised of removing phosphates and nitrates from the water supply. Substances like activates carbon and sand are among the most commonly used materials that assist in this process.