Backwashing for Enhancing Quartz Sand Filter Performance

  
Quartz sand filters are devices that primarily use quartz sand as the filtration medium and are widely used in industrial water treatment systems. They effectively remove impurities such as suspended solids, silt, and organic matter from water, ensuring water quality meets requirements while maintaining the stable operation of the system. The importance of quartz sand filters in the field of water treatment cannot be underestimated, but to keep them running efficiently, regular backwashing operations are indispensable. This article will explore in detail the working principle of quartz sand filters, the setting of backwash parameters, operation methods, factors determining the frequency of backwashing, and the importance of backwashing.

Working Principle of Quartz Sand Filters

 
The core working principle of quartz sand filters is the physical interception by the quartz sand medium to remove suspended particles and other impurities from water. As raw water passes through the filter, impurities are retained in the filter layer, and the filtered clear water flows out from the other end of the device. Over time, the accumulation of impurities in the filter layer increases, leading to increased filtration resistance, reduced water output, and even affecting the filtration effect. Therefore, regular backwashing is necessary, which can clear the accumulation in the filter material and restore the filter to its initial state.

Backwash Parameter Settings for Quartz Sand Filters

 
Backwashing is one of the most important parts of quartz sand filter maintenance, and the effectiveness of backwashing is directly related to the setting of parameters. Here are some suggestions for key parameter settings.

1. Backwash Inlet Temperature

The temperature of the backwash inlet should be controlled between 5-45°C. This temperature range ensures that the water flow has appropriate fluidity while avoiding thermal stress damage to the equipment materials.

2. Filter Layer Height

The height of the filter layer directly affects the backwash parameters. For a quartz sand filter layer with a height of 800-1200 millimeters, it is recommended to set the filtration operation flow rate at 8.7 meters per hour, the operating flow at 70 cubic meters per hour, the backwash water intensity at 12-14 liters per hour.

3. Equipment Design Pressure

To ensure the safe operation of the equipment, the design pressure of the quartz sand filter should be controlled within 0.6 MPa, and the hydrostatic test pressure should be 0.8 MPa.

4. Backwash Expansion Height

During the backwashing process, the filter material will expand. It is recommended to control the expansion height to about 40% of the filter layer. This can effectively prevent the filter material from overflowing or damaging the equipment due to excessive expansion.

5. Operating Pressure Differential

The operating pressure differential is an important parameter for measuring the working state of the filter. Under normal conditions, the operating pressure differential should be controlled within 0.05 MPa, and the output pressure differential should not exceed 0.1 MPa.

Backwash Operation Methods for Quartz Sand Filters

The steps of backwashing operation are complex but crucial. Here is a detailed operation process.

1. Preparation Work

First, check whether the water level in the backwash tank is at a high level, which should exceed the water level line to ensure sufficient water volume during backwashing. If the water volume is insufficient, it may lead to poor backwashing effect or equipment damage.

2. Start Backwashing

Open the backwash drainage valve, start the backwash pump, and start the backwashing operation, with a time control of about 5 minutes. This process will wash away the impurities in the filter material and restore the filter material's filtration capacity.

3. Normal Drainage Operation

After the backwash is finished, close the backwash inlet valve and backwash pump, then open the normal drainage valve and air vent valve to drain the water to the middle of the filter water level sight glass, with a drainage time of 10 minutes.

4. Air Scour

Close the normal drainage valve, open the air inlet valve for air scour, with a time of 3-5 minutes. Air scour uses the friction between air bubbles and filter material to further remove residual impurities in the filter material.

5. Re-backwash

Close the air inlet valve and air vent valve, restart the backwash pump, open the water inlet valve, and re-perform backwashing for 10-15 minutes. This step can ensure that the filter material is thoroughly cleaned.

6. Rest and Inspection

After the backwash is completed, close all valves, rest for 3 minutes, and check the condition of the filter material to ensure there is no filter material running or stratification.

7. Final Normal Wash

Finally, perform a normal wash to ensure that all impurities in the system are completely removed.

Backwash Frequency of Quartz Sand Filters

 
The backwash frequency of quartz sand filters is not fixed, but determined according to the changes in the quality of the inlet water and the product water. Generally, the backwash frequency is once every 4-8 hours, with 3-6 backwashes per day. If the inlet water quality is poor and the impurity content is high, the backwash frequency needs to be increased to ensure the efficient operation of the equipment. On the contrary, if the water quality is good, the backwash frequency can be appropriately reduced.

Importance of Backwashing for Quartz Sand Filters

 
Regular backwashing is key to ensuring the long-term efficient operation of quartz sand filters. Over time, impurities in the filter material will gradually accumulate. If not removed in time, these impurities will clog the filter layer, leading to reduced water pressure, reduced flow, and ultimately affecting the filtration effect. In addition, not backwashing in time will also increase the system's energy consumption and reduce work efficiency.
 
There are mainly two types of backwashing methods for quartz sand filters: air-water backwash and water backwash. Air-water backwash enhances the backwashing effect through the friction between air bubbles and filter material, as well as the interaction between filter material particles. Water backwash relies on the friction between water flow and filter material, as well as the friction between sand particles, and is usually suitable for smaller filters.
 
Quartz sand filters are commonly used equipment in the water treatment industry, widely welcomed for their low cost and significant filtration effect. However, to ensure that they always maintain the best performance, regular backwashing operations are essential. By setting backwash parameters reasonably, strictly following the operation process for backwashing, and adjusting the backwashing frequency according to the actual water quality, the operation efficiency and product water quality of the quartz sand filter can be effectively maintained, and the service life of the equipment can be extended. In practical applications, users should fully recognize the importance of backwashing and take corresponding measures to ensure the long-term stable operation of the equipment.