Large suspended particles are removed by the upper portion of the filter while smaller particles are removed lower in the filter. Thus, the entire depth of the filter bed is used. Chemical pre-treatment is frequently part of the filtration process for particle removal. Colloidal particles commonly have an electrical charge on them. Then, the particles can cling to one another and to the surface of the filter media.
Higher clarity is obtained in the filtration process by the proper use of chemical pre-treatment.
If an operator is present to make adjustments for variations in the raw water, filtered water improvements in the range of 93 - 95 percent can be achieved. As the filter operates, it accumulates the particles in the filter bed. This increases the pressure loss through the filter. When the pressure loss is 5 - 10 psi higher than at the beginning of the cycle, the filter should be regenerated. Operating beyond this point will result in poor filter performance .