Select incorrect w.r.t. sewage treatment plants.

Options

A. In anaerobic sludge digester, gases like methane, `H_2S` and `CO_2` are also produced.
B. Primary treatment of sludge is based on sequential filtration and sedimentation.
C. Bacterial flocs are allowed to sediment in settling tank when BOD of sewage is high.
D. Activated sludge is pumped into anaerobic sludge digesters to digest the bacteria and fungi

Answer

To determine the incorrect statement regarding sewage treatment plants, we need to analyze the options provided in the context of sewage treatment processes. Here’s a step-by-step solution:

### Step 1: Understand the Types of Treatment in Sewage Treatment Plants
Sewage treatment typically involves three main stages:
1. **Primary Treatment**: Physical removal of solids.
2. **Secondary Treatment**: Biological treatment to degrade organic matter.
3. **Tertiary Treatment**: Advanced treatment for further purification.

### Step 2: Analyze the Options
Let's consider the options mentioned in the video transcript:
1. **Anaerobic Digesters**: These are used in the secondary treatment stage to break down organic matter in the absence of oxygen, producing gases like methane, carbon dioxide, and water.
2. **Sedimentation Plant**: This is part of the primary treatment where solids settle out of the sewage.
3. **Biological Treatment Plant**: This refers to the secondary treatment process that utilizes microorganisms to decompose organic matter.
4. **Filtration Plant**: This is often part of tertiary treatment, where remaining solids and impurities are filtered out.
5. **Polythene Plant**: This option seems out of place as it does not relate to sewage treatment processes.

### Step 3: Identify the Incorrect Option
Upon reviewing the options:
- The **Polythene Plant** does not belong to the sewage treatment process and is therefore the incorrect option.

### Conclusion
The incorrect statement with respect to sewage treatment plants is the mention of a **Polythene Plant**.

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