Which one of the following impurities is easiest to remove from wastewater ?

Options

A. Bacteria
B. Colloids
C. Dissolved solids
D. Suspended solids

Answer

To determine which impurity is easiest to remove from wastewater, let's analyze the options provided: bacteria, colloid, dissolved solid, and suspended solid.

### Step-by-Step Solution:

1. **Understanding Suspended Solids**:
- Suspended solids are larger particles that do not dissolve in water, such as sand, silt, and small stones.
- Due to their size and weight, they tend to settle at the bottom of the water body over time.

2. **Separation Techniques for Suspended Solids**:
- Suspended solids can be easily removed using physical methods such as sedimentation and filtration.
- In sedimentation, the water is allowed to sit, and the heavier particles settle at the bottom.
- Filtration involves passing the water through a filter that traps the solid particles.

3. **Understanding Bacteria**:
- Bacteria are microscopic organisms that cannot be seen with the naked eye.
- Their removal from wastewater typically requires more advanced techniques, such as biological treatment or disinfection methods (e.g., chlorination), making them harder to remove.

4. **Understanding Colloids**:
- Colloids are small particles that remain suspended in water and do not settle easily.
- They require special treatment methods, such as coagulation and flocculation, to remove.

5. **Understanding Dissolved Solids**:
- Dissolved solids are substances that have completely dissolved in water, such as salts.
- Removing dissolved solids usually requires processes like reverse osmosis or distillation, which are more complex.

6. **Conclusion**:
- Among the options provided, suspended solids are the easiest to remove from wastewater due to their larger size and the effectiveness of simple physical removal methods.

### Final Answer:
The easiest impurity to remove from wastewater is **suspended solid**.

---