Which process is used to restore filter performance by removing trapped solids?

• A. Aeration
• B. Chlorination
• C. Filtration
• D. Backwashing

Answer: (D)

Backwashing is used to restore filter performance by removing trapped solids from the filter media. As a filter collects particles, the bed becomes clogged, increasing resistance and reducing efficiency. Reversing the flow through the filter (often with air scour) lifts and loosens the accumulated solids so they are flushed out to waste, helping the bed regain porosity and the ability to remove particles effectively again. This cleaning step is distinct from the normal filtration process, which captures solids, or from other treatments like aeration (which adds air for oxidation/gas transfer) and chlorination (which disinfects).