In treatement of waste, biological treatement is

Options

A. Primary treatement
B. Secondary treatement
C. Tertiary treatment
D. Reverse osmosis stage.

Answer

### Step-by-Step Solution:

1. **Understanding Waste Treatment**: Waste treatment involves various processes to remove contaminants from waste materials, particularly sewage. The treatment process can be divided into three main stages: primary, secondary, and tertiary treatment.

2. **Primary Treatment**: This is the first stage of waste treatment. It involves the physical removal of large solids and debris from sewage through filtration. This process does not involve biological methods and is primarily mechanical.

3. **Secondary Treatment**: This stage is crucial for biological treatment. It utilizes decomposing microbes to break down organic matter in sewage. The microbes consume the organic waste, effectively reducing the pollution load in the water. This process is essential for treating sewage biologically and is often referred to as biological treatment.

4. **Tertiary Treatment**: The final stage of waste treatment involves advanced chemical processes to further purify the water. This stage is not biological and focuses on removing remaining contaminants through chemical means.

5. **Conclusion**: Based on the definitions and processes involved, secondary treatment is the biological treatment stage in waste management, as it employs microbes to decompose organic sewage.

### Final Answer:
In the treatment of waste, biological treatment is referred to as **secondary treatment**.

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