Excessive backwashing time for multi-media filters can cause irreversible damage to the equipment's lifespan through three paths: filter media wear, water distribution failure, and component aging. Specifically:
I. Filter media layer: Accelerated wear and premature failure
Accelerated filter media wear
Prolonged, high-intensity backwashing (>15 minutes) will increase the friction frequency of filter media particles such as quartz sand and anthracite. The annual wear rate exceeds 5%, which leads to a reduction in filter media particle size, a decrease in adsorption sites, and a 30%-50% decrease in filtration efficiency.
Wear-out filter media cannot restore its original dirt-trapping capacity and needs to be replaced in advance (normal lifespan is 5-8 years, but excessive backwashing may shorten it to 2-3 years).
Filter media loss and stratification disorder
Excessive backwash water/airflow velocity (e.g., >12L/(m²・s) in anthracite coal seams) will directly wash away the upper lightweight filter media.,
Excessive backwash water/airflow velocity (e.g., >12L/(m²・s) in anthracite coal seams) will directly wash away the upper lightweight filter media. This results in insufficient filter layer thickness, disruption of the "coarse top, fine bottom" gradient structure, short-circuiting of water flow, and an increase in effluent turbidity to 2-5 NTU.
After the filter media is lost, it needs to be replenished with the same specification of filter media. However, mixing new and old filter media will further reduce the filtration stability and cause irreversible performance degradation.
II. Water Distribution System: Structural Damage and Functional Loss
This can lead to filter cap breakage, screen plate displacement, or perforated pipe cracks, resulting in uneven water flow distribution and localized loss of filter media due to excessive scouring, requiring shutdown and replacement of the water distribution device.
If the backwashing time is too long but the intensity is insufficient (e.g., <10L/(m²・s)), impurities will embed deep into the filter media and form clumps. Even if the time is shortened later, it will be difficult to recover, and some of the aged filter media will need to be replaced (cost increases by 30%-50%).
Frequent backwashing (e.g., more than 3 times a day) will shorten the life of the pneumatic valve seal from 2 years to 1 year, accelerate the wear of the backwash pump bearing, and increase energy consumption by 10%-20% (each backwash consumes about 0.1-0.2 kWh/m³).
If the water is not completely drained after backwashing (such as residual acidic water), it will accelerate the electrochemical corrosion of the inner wall of the filter tank and the supporting structure, shortening the service life of the equipment.
