Home › NEET UG › Biology › Microbes in Human Welfare ›  The 'activated sludge' obtained in secondary sewage treatment:
AIs discarded immediately
BA small portion is recycled back to the aeration tank as inoculum; the rest is sent to anaerobic sludge digesters where biogas is produced
CIs dried and burned directly
DIs used as fertiliser without any further processing
Answer & Solution
Correct answer: B. A small portion is recycled back to the aeration tank as inoculum; the rest is sent to anaerobic sludge digesters where biogas is produced
After BOD reduction, the bacterial flocs settle as **activated sludge**. A **small portion is recycled** to the aeration tank (inoculum). The **bulk goes to anaerobic sludge digesters**, where anaerobic bacteria produce **biogas** (CH₄, H₂S, CO₂, H₂).
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