Which of the following is put into Anaerobic sludge digester for further sewage treatment?

Question

Accepted Answer

D. 1. Understand the flow of sewage treatment — after primary treatment, the wastewater passes into an **aeration tank** where microbes grow and form flocs, then it moves to a **settling tank**.

2. The sediment that settles down in this settling tank is called **activated sludge**.

$$
	ext{Settling tank sediment} ightarrow 	ext{Activated sludge}
$$

3. A small part of this activated sludge is pumped back into the aeration tank to maintain the microbial population there, but the **major remaining part** is pumped into large tanks called **anaerobic sludge digesters**.

Therefore

$$
	ext{Activated sludge (major part)} ightarrow 	ext{Anaerobic sludge digester}
$$

4. Eliminate the other options — effluents of primary treatment go to the aeration tank, and floating debris/primary sludge are removed earlier in the primary treatment stage, not sent to the anaerobic digester.

Hence, the answer is **D (Activated sludge)**.