Question

Slow sand filter is similar to rapid sand filter in terms of coagulation.

(a) True

(b) False

I have been asked this question in an online interview.

My question is taken from Treatment Processes topic in division Effluent Treatment of Bioprocess Engineering

Answer 1

The correct answer is:

(b) False

Slow sand filters and rapid sand filters are both used for water treatment, but they differ in their design and operation, especially in terms of coagulation.

• Slow sand filters: These rely primarily on biological processes that develop on the surface of the sand. Coagulation typically happens due to the slow filtration rate and the interaction between microorganisms and particulate matter. It does not usually require an external coagulating agent, as the natural biological layer (schmutzdecke) helps with particle removal.

• Rapid sand filters: These use coagulants (such as alum) to agglomerate particles before filtering the water through sand at a much faster rate. The coagulation step in rapid sand filters is much more dependent on chemical coagulants, and the filtration process is faster.

Thus, slow sand filters do not rely on coagulation in the same way as rapid sand filters, making the statement false.