What Are The Backwashing Steps For Activated Carbon Filters?

The core of the backwash operation of activated carbon filter is to " gently remove the suspended particles on the surface of the filter media".",
The core of the backwash operation of an activated carbon filter is to " gently remove suspended matter from the filter media surface, unclog the microporous channels, and avoid wear and tear of the activated carbon ." It must follow the standardized process of "preparation → exhaust → backwash → standstill → forward wash → resume operation." The parameters must be precisely controlled based on the low density and easy wear of activated carbon. The specific steps are as follows:

1. Preparation before backwash: check status and set parameters

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Equipment and valve inspection
Close the normal operation valve: first close the water inlet valve , wait until the pressure in the tank drops below 0.05MPa (the pressure gauge pointer is stable), then close the water outlet valve to prevent the raw water and backwash water from mixing and contaminating the filter media;

Verify the backwash valve: confirm that the backwash inlet valve , backwash drain valve , and top exhaust valve are flexible (the manual valve is not stuck, and the electric valve responds promptly), and there is no leakage in the closed state (no water droplets on the flange interface and valve sealing surface);

Check the backwash power: If it is driven by a water pump, start the backwash pump and run it at no load for 10-20 seconds to confirm that the pump body has no noise, the seal has no leakage, and the outlet pressure gauge shows normal (the pressure must meet the backwash intensity requirements, usually 0.2-0.3MPa); if it is gravity backwash, confirm that the water level in the backwash tank meets the standard (provide sufficient backwash head).

Setting key backwash parameters

Backwash intensity: 10-15 L/(m²·s) (real-time monitoring by flow meter);

Filter material expansion rate: 15%-25% (observed through the tank mirror, the activated carbon layer expands evenly but does not overflow);

Backwash time: 5-8 minutes (the turbidity of backwash drainage is ≤5NTU).

2. Core backwash process: staged control to ensure cleaning effect

1. Exhaust and pressure relief (key step, prevent gas blockage and

Open the exhaust valve on the top of the filter and slowly open the backwash water inlet valve
Open the filter and slowly open the backwash water inlet valve (gradually adjust the opening from 1/4 to 1/2) to allow the backwash water to enter the tank at a low flow rate:

Purpose: To discharge the residual air in the tank to avoid the air being compressed and forming "air lock" -

Judgment standard: When the exhaust valve continuously discharges a stable water flow (no bubbles emerge), close the exhaust valve and enter the formal backwash stage (usually takes 1-2 minutes).

2. Formal backwash: control intensity and

Gradually open the valve (from 1/2 to full open), stabilize the backwash intensity at 10-15 L/(m²・s) using the pressure gauge and flow meter, and monitor the activated carbon status through the sight glass:

Normal state: The activated carbon layer expands evenly (e.g. original thickness 1.2m, 1.4-1.5m after expansion), particles collide and rub slightly, surface suspended matter (silt, colloid) is stripped off, and backwash drainage gradually turns clear from yellow-brown;

Exception handling:

If the expansion rate is too low (<15%): properly open the backwash water inlet valve or increase the backwash pump frequency until the expansion meets the standard;

If the expansion rate is too high (>25%): immediately close the backwash water inlet valve and reduce the intensity to below 12 L/(m²・s) to prevent the loss of fine particles of activated carbon;

Termination judgment: Check the turbidity of backwash drainage every 1 minute. When the turbidity is ≤5NTU, close the backwash water inlet valve and stop backwashing.

3. Let the activated carbon settle naturally after backwashing

Keep the backwash drain valve open for 1-2 minutes to drain the remaining backwash water and impurities in the tank, then close the backwash drain valve and let the activated carbon settle naturally for 5-10 minutes:

Purpose: To prevent the activated carbon layer from being disturbed due to sudden cessation of washing (fine particles accumulate at the top and coarse particles sink to the bottom), and to prevent the water flow from being "short-circuited" (unfiltered water directly penetrates) during subsequent operation;

Observation standard: After standing, the interface of the activated carbon layer is flat, without obvious stratification or depression, indicating that the sedimentation state is good.

3. Recovery after backwash: forward wash meets the standard and put into operation

After backwashing, a small amount of impurities may remain on the surface of the activated carbon, which needs to be removed by "forward washing" (flushing in the normal filtering direction) to ensure that the effluent water quality is qualified:

Forward wash operation: Slowly open the water inlet valve (open 1/3), let the raw water enter the tank in the normal filtration direction, and at the same time open the forward wash drain valve (or temporarily use the outlet valve to drain), and control the forward wash flow rate to 50%-70% of the design flow rate (for example, if the design is 15m³/h, the forward wash flow rate is 8-10m³/h) to avoid disturbing the newly settled filter material layer;

Compliance assessment: Check the forward wash drainage water quality every 1-2 minutes (core turbidity measurement, drinking water/food industry requires simultaneous measurement of residual chlorine/COD). When the drainage turbidity is ≤1NTU (or residual chlorine ≤0.05mg/L, COD ≤5mg/L, meeting the design standard), close the forward wash drainage valve.

Resume operation: Slowly open the water outlet valve (gradually adjust the opening from 1/3 to full open), monitor the filter inlet and outlet pressures (normal pressure difference 0.02-0.03MPa) and the outlet water quality, and officially resume operation after confirming that there are no abnormalities.

4. Special case handling: chemical-assisted cleaning of sticky impurities

If the raw water contains sticky impurities (such as oil, humic acid, iron and manganese pollution), conventional backwashing cannot be completely cleaned, and chemical auxiliary steps are required:

Chemical soaking: Before backwashing, drain the water in the tank and inject 5%-8% dilute hydrochloric acid (to remove iron and manganese) or 2%-4% sodium hydroxide solution (to remove oil and organic matter). Soak for 2-4 hours to destroy the adsorption bond between impurities and activated carbon.

Auxiliary backwash: Follow the conventional backwash process, the backwash intensity can be fine-tuned to 12-14 L/(m²・s), and the backwash time can be extended to 8-10 minutes to ensure that impurities are completely removed;

Neutralization flushing: After chemical backwashing, use clean water to flush until the pH of the drainage returns to neutral (6-8) to avoid residual chemicals contaminating the downstream water quality.

Summarize

The core of activated carbon filter backwashing is " gentle cleaning and precise control ." By exhausting to prevent impact, controlling the intensity to prevent loss, and allowing the filter to rest to prevent turbulence, the filter removes suspended solids while protecting the activated carbon's structure and adsorption activity. Proper operation can achieve a surface impurity removal rate of over 90% on the activated carbon, restoring the pores to a clear state, effectively extending the activated carbon's service life and ensuring long-term, stable filter performance.