The turbidity of water applied to rapid sand filter is less than 35-40ppm.

Definition of Turbidity:
Turbidity is the measure of the cloudiness or haziness of a fluid caused by suspended solid particles. In water treatment processes, turbidity is an important parameter used to assess the effectiveness of filtration systems.

Role of Rapid Sand Filter:
Rapid sand filters are widely used in water treatment plants to remove suspended particles and impurities from water. These filters consist of a bed of sand through which water is passed under pressure. The sand bed acts as a physical barrier, trapping and removing solid particles from the water.

Importance of Turbidity in Rapid Sand Filtration:
Turbidity is an essential parameter to monitor in rapid sand filtration because it directly affects the efficiency of the filtration process. High turbidity levels indicate the presence of a large number of suspended particles, which can clog the filter bed and reduce its capacity to remove impurities.

Optimum Turbidity Range:
To ensure effective filtration, the turbidity of water applied to a rapid sand filter should be within a certain range. This range is typically less than 35-40ppm (parts per million).

Reasons for the Optimum Turbidity Range:
1. Filter Efficiency: Rapid sand filters are designed to operate optimally within a specific turbidity range. When the turbidity exceeds this range, the filter bed becomes overloaded with suspended particles, reducing its ability to effectively remove impurities.
2. Filter Clogging: High turbidity levels can lead to accelerated filter clogging. When the filter bed gets clogged, the flow rate of water through the filter decreases, and the filter needs to be backwashed more frequently to maintain performance.
3. Water Quality: Water with high turbidity may contain pathogens, organic matter, and other contaminants that can pose health risks. By maintaining turbidity within the recommended range, the filter ensures the removal of these harmful substances, resulting in cleaner and safer water.

Conclusion:
In conclusion, the turbidity of water applied to a rapid sand filter should be less than 35-40ppm to ensure optimal filtration efficiency, prevent filter clogging, and maintain water quality standards. Monitoring and controlling turbidity levels are crucial in water treatment processes to ensure effective removal of suspended particles and provide safe and clean drinking water.