How To Optimize The Backwashing Effect Of Multi-media Filters? - News

Optimizing the backwashing effect of multi-media filters requires attention to parameter control, filter media maintenance, water and air source optimization, trigger timing adjustment, and auxiliary measures. Specific methods are as follows:

I. Optimize backwashing parameters

Backwash intensity

Adjust the strength according to the type of filter media to ensure that the filter media expands appropriately and does not leak.

Quartz sand filter media: water washing strength 10-15 L/(m²・s), expansion rate 15%-20%; Anthracite filter media: water washing strength 8-12 L/(m²・s), expansion rate 20%-25%.

The air washing intensity is typically 10-18 L/(m²・s) to ensure that the airflow can disturb the deep filter media.

Adjustment method: Control the water flow rate by adjusting the valve opening or using a variable frequency pump, and monitor the flow meter in real time to avoid excessively high or low intensity.

Backwash time

The air washing time is 3-5 minutes. If the impurities are tightly adhered, it can be extended to 5-8 minutes.

Wash for 5-10 minutes, ending when the turbidity of the effluent is ≤5 NTU.

Wash for 2-3 minutes until the turbidity of the effluent is ≤1 NTU.

Air-water flushing sequence

Standard procedure: First, air wash (to remove impurities) → then water wash (to remove impurities), to prevent impurities from being compacted.

High turbidity/high viscosity impurities: "Air-water mixed washing" is used to enhance the impurity removal effect.

II. Optimize the state of the filter media

Controlling filter media gradation and filling amount
The filter media is filled in a gradient of "coarse on top and fine on the bottom" to avoid uneven pore size caused by mixed particle sizes.

The filling height should be moderate, typically 1.5-2 times the filter diameter.

Regularly check filter media wear and caking.

If a significant reduction in filter media is observed after backwashing, it should be replenished promptly, and the filter cap/distributor should be checked for damage.

If the filter media becomes caked, the machine must be stopped and the media manually loosened or replaced. If necessary, it can be soaked and cleaned with dilute hydrochloric acid.

III. Optimize backwash water and air sources

Backwash water
Use the filter effluent as backwash water first to avoid secondary pollution caused by suspended solids in the raw water.

Backwash water needs to be pretreated to prevent calcium and magnesium ions, iron and manganese ions from forming scale on the filter media surface.

Compressed air
The compressed air used for air washing needs to be de-oiled and de-watered to prevent oil from adhering to the filter media or water from mixing with impurities to form clumps.

IV. Optimize the timing of backwash triggering

Pressure difference + water quality combined triggering
The system combines inlet and outlet pressure difference (up to 0.08-0.1MPa) and effluent turbidity (exceeding the set value, such as 3NTU) as trigger indicators, which better reflects the actual pollution level.

Avoid frequent short rinses
Too short backwash intervals may result in ineffective backwashing. It is necessary to check whether the influent water quality has suddenly deteriorated and adjust the pretreatment.

V. Auxiliary Optimization Measures

Regularly perform enhanced backwashing

In response to seasonal water quality fluctuations, an enhanced mode of "extending air washing time + increasing water washing intensity" is adopted 1-2 times per month to thoroughly remove deep impurities.

Optimize water/air distribution devices
Ensure that the water distributor and air distribution device are evenly distributed to avoid creating "dead zones" due to insufficient local flushing intensity.