In an effort to conserve water used to backwash their water treatment plant filters, Industrial Fluid Management was asked to design a sand filter scenario that would increase the time between required backwashes.
The village uses ground water with a high iron content (>0.6 ppm) and had employed chlorine oxidation and pressurized sand filters to remove the precipitated iron. With the rising costs of both water and the management of the wastewater from their backwash, they wished to investigate filtration that would last longer before breakthrough.
IFM answered this request by designing a depth filter, or multimedia filtration grid as it is sometimes called. By putting a fine, dense media on the bottom of the filter column and working up to larger media on top (through two other layers), an â€˜invertedâ€™ filter is made.
In the down-flow column, the largest particles are taken out in the top part of the bed, working down through to the bottom layer where the finest of particles are removed. Conversely, during the backwash, the larger, heavier particles are closer to the top, making removal easier. The backwash flow is adjusted to remove even the fine particles and re-stratifying the multi-media.
This depth/multi-media filtration is capable of removing multiple times the pounds of particles that traditional sand filters remove. Sand filters perform all of the filtration on the top of the sand bed, causing a matted filter cake, and requiring more frequent backwashing.
The rebed was completed by IFM and was brought on-line. The quality of the filter's effluent was dramatically improved and the duration of on-line run times were increased significantly.