Total backwashing time of activated carbon filter should be determined based onwashing method (single water-flushing/air-water combined-flushing), degree ofactivated carbon fouling, and type of filter media. The main principle is "tocompletely remove impurities without wasting water resources". The time division is:
I. Single water backwash (most frequent)
Total time: 15-25 minutes
Total duration: 15-25 min, divided in stages:
Low intensity initial flush :2-3 minutes (8-10L intensity)
High intensity Main Flush: 10~15min (intensity 10~20L/(m2 s), core stage, usinghigh flow rate water to strip impurities from the surface of the activated carbon untilthe drainage becomes clear;
Low Intensity Rinsing : 2-5 min (intensity 5-8 L/(m2 s)) Activated carbon particlessettle steadily and filter bed structure andThe main principle is "to removeimpurities thoroughly without wasting water resources."
II. Combined Air-Water Backwashing (Applicable to)
Total time :20 - 30 minutes. Broken down into stages :
Air-water co-flushing: 5~8 minutes (air flushing 10~15L/(m2 . s) + water flushing5~8L/(m2 . s)), air and water cooperate to flush, and improve the removal ofimpurities;
High-intensity water flushing : 8~10 minutes (intensity 12~18L/(m2 . s)) to wash awaythe loosened impurities from the tank;
Low Intensity Flushing: 2-5 minutes at 5-8 L/(m2 s) to stabilise the filter bed andwash out residual impurities.
III. Special Situations - Adjustments
When pollution is heavy (eg water ingress)
Low temperature environment (<5°C): Due to the increase of water viscosity, therinsing efficiency is reduced, and the total time is increased by 20%~30% (i.e., theusual 20 minutes is extended to 24~26 minutes).
Coconut shell activated carbon (high hardness, well-developed pores): main flushingtime can be reduced by 2-3 minutes, coal-based activated carbon (lower strength):main flushing time should be increased by 2-3 minutes to avoid incomplete rinsing.
Main criteria of the judgement
The backwashing time is not a fixed value, the final standard is that "the drain wateris clear and transparent, without obvious impurities, and the filter bed pressuredifference returns to the initial value (0.05~0.1MPa) after backwashing".
If the drainage remains turbid, even after the preset time, the main flushing timeneeds extending.
If the drainage is clear before the rinsing stage, the rinsing stage can be startedearlier to avoid excessive rinsing which could cause loss of the activated carbon.
