Question

What are the stages involved in the secondary and tertiary treatment of water?

Answer 1

Hint: In the secondary treatment of water removal of dissolved or colloidal compounds takes place. In the tertiary treatment of water the removal of the remaining inorganic compounds takes place.

Complete Answer:In both secondary and tertiary treatment of water there exists many different processes which are undertaken to treat water. Let us now look at these processes.

In the secondary treatment of water dissolve compounds are removed. It includes using the following processes :-

Biofiltration - In this process the effluent is made to go through a packed bed of gravel, broken rock, etc to remove the solid particles.

Aeration - This process is also known as activated sludge. In this process the water is treated with microbes and aeration. These microbes metabolize the contaminants into simpler forms.

Oxidation - In this process natural water bodies like lagoons are used to treat water. Water is allowed to stand in such water bodies for weeks and this leads to organic components undergoing decomposition. Further carbon dioxide, ammonia, nitrate and methane are released. Organic sludge settles at the bottom.

In the tertiary treatment removal of the remaining inorganic compounds takes place and this is essential for the removal of phosphates and nitrates. In this stage sand filters are used, these sand filters consist of alum due to which solid particles come together to form floc.

Chlorinated tank is used for further treatment, the chlorine removes microorganisms including bacteria, parasites and viruses. The floc is removed from time to time.

Note: Water treatment is very important for human health. Water treatment helps humans in both drinking as well as for irrigation use. The three most commonly used chemicals while treating water are - chlorine, chlorine dioxide and ozone.