Question

Sort the following events in primary, secondary and tertiary treatments of sewage.

• A. Discharge
• B. Sedimentation
• C. Pathogen removal
• D. Oxidation ponds

Answer 1

Sewage treatment is done in 3 steps. The primary treatment involves the removal of bulky solid waste using sedimentation tanks. In the secondary treatment, micro-organisms oxidise the organic matter. Sludge produced during this process is used as manure. The tertiary stage involves removal of harmful chemicals, metals and pathogens from this water. Now, this water is not potable but it can be safely discharged into water bodies or used for agriculture.