Question

Define sewage. Describe the biological treatment of sewage in brief.

Hint:

Biological sewage treatment = microbes + aeration tank → activated sludge → biogas.

Answer 1

Step 1: Definition of sewage.
Sewage is the wastewater released from homes, industries, hospitals, and other sources. It contains organic matter, harmful microorganisms, suspended solids, and toxic chemicals.

Step 2: Biological treatment of sewage.
The biological treatment mainly refers to the secondary treatment of sewage, where microbes decompose organic matter. It includes: \begin{enumerate} \item Aeration tank: Sewage is pumped into aeration tanks where air is supplied. Aerobic microbes grow and form activated sludge. \item Decomposition: Microbes digest organic matter, reducing BOD (Biological Oxygen Demand). \item Settling tank: Activated sludge is allowed to settle. A part is recycled, and the rest is sent to anaerobic sludge digesters. \item Methane production: Anaerobic microbes decompose the sludge and release biogas (methane, CO₂, hydrogen sulphide). \end{enumerate}

Step 3: Conclusion.
Biological treatment reduces organic pollutants and makes sewage water safe for disposal into rivers or reuse in irrigation.