Minimum Weir Loading Rate of Primary Clarifier
To determine the minimum weir loading rate of a primary clarifier, we need to consider the design and capacity of the clarifier. The weir loading rate is typically expressed in cubic meters per square meter per day (m3/m/day) and is an important parameter for ensuring proper sedimentation and settling of solids in the clarifier.

Calculation:
- The minimum weir loading rate for a primary clarifier is usually around 125,000 m3/m/day. This value ensures that the clarifier is able to effectively remove solids and other impurities from the wastewater.
- A high weir loading rate indicates that the clarifier is being overloaded with solids, which can lead to poor effluent quality and reduced efficiency. On the other hand, a low weir loading rate may result in insufficient treatment of the wastewater.
- By maintaining a minimum weir loading rate of 125,000 m3/m/day, the primary clarifier can operate efficiently and effectively, ensuring that the wastewater is properly treated before being discharged.

Importance of Weir Loading Rate:
- Proper weir loading rate is essential for the optimal performance of the primary clarifier.
- It helps in achieving the desired level of sedimentation and settling of solids.
- Maintaining the minimum weir loading rate ensures that the clarifier operates within its design capacity and provides adequate treatment.
Therefore, the correct answer to the question is option 'A' (125,000 m3/m/day) as the minimum weir loading rate for a primary clarifier.