As a core pretreatment device in water treatment processes, the multi-media filter utilizes a deep filtration mechanism that combines layered filter media design with physical retention principles to achieve precise, graded interception of impurities in water. The core of this equipment lies in leveraging the differences in particle size, density, and surface properties of various filter media to construct a gradient filter layer structure with coarser particles at the top and finer particles at the bottom, allowing water to undergo a multi-stage purification process as it flows through.
When the water to be treated enters from the top of the filter, it first comes into contact with the upper layer of filter media, such as anthracite, which has a larger particle size and higher porosity. This type of filter media has a rough surface and open pores, enabling it to quickly trap larger suspended solids in the water, such as algae, silt clumps, and rust particles. Its coarse-mesh-like mechanism not only reduces the burden on subsequent filter layers but also captures some tiny particles through surface adsorption, forming a preliminary filtration barrier. The loose structure of the upper filter media gives it a high dirt-holding capacity, allowing it to accommodate a large amount of impurities without easily clogging, ensuring the stability of the entire filtration cycle. After water penetrates the upper filter media, it enters the middle layer of quartz sand filter media with smaller particle sizes. The quartz sand particles are densely packed, and the pore size is significantly reduced, forming a medium-efficiency filtration layer. At this stage, the water flow velocity slows down due to increased filter media resistance, and residual suspended solids, colloids, and organic matter in the water are further trapped through mechanical resistance and adsorption. The surface electrical properties and microporous structure of quartz sand give it excellent adsorption performance for charged colloidal particles, effectively agglomerating dispersed particles into larger flocs that are then intercepted by the filter layer. This process significantly reduces the effluent turbidity, creating favorable conditions for the subsequent fine filtration.
The bottom layer, magnetite or manganese sand filter media, constitutes the high-efficiency fine filtration layer, with the smallest particle size, highest density, and extremely fine pore structure. When the water reaches this layer, the remaining fine suspended particles, bacteria, and some dissolved organic matter are completely trapped by this layer. The high density of magnetite facilitates settling during backwashing, maintaining the stability of the filter bed structure over a long period. Manganese sand, through catalytic oxidation, removes iron and manganese ions from the water, further improving water quality. The precise filtration of the lower filter media ensures that the effluent meets the requirements of subsequent treatment processes; its retention efficiency directly determines the performance ceiling of the entire filtration system.
The stratified retention mechanism of the multi-media filter relies on the density difference and particle size gradient design between the filter media. The density difference between the upper coarse filter media and the lower fine filter media creates natural stratification. During backwashing, water flow disturbance rearranges the filter media according to density, avoiding layer mixing. This structure ensures that impurities are retained stepwise according to particle size during filtration, preventing large particles from directly impacting the lower fine filter media, thus extending the filter media's lifespan. Simultaneously, the gradient filter bed increases the impurity holding space, fully utilizing the depth of the entire filter bed and significantly increasing the throughput per filtration cycle.
The backwashing process is crucial for the long-term stable operation of the multi-media filter. When the filter bed resistance reaches a set threshold or the effluent quality declines, reverse water flow enters from the bottom, causing the compacted filter media to expand and fluidize. At this time, the filter media particles collide with each other under the shear force and friction of the water flow, shearing off impurities trapped on the surface. Compressed air scrubbing further enhances the cleaning effect, ensuring the filter media regains its initial filtration capacity. After backwashing, the filter media naturally settles under gravity, re-stratifying according to density differences, preparing for the next cycle of high-efficiency filtration.
The multi-media filter achieves deep purification of impurities in water through the synergistic effect of stratified filter media and backwash regeneration technology. Its design concept balances filtration efficiency and operational stability, adapting to different water quality requirements by adjusting the filter media combination and reducing operating costs by optimizing backwash parameters. This mechanism makes it irreplaceable in the pretreatment stage of advanced treatment processes such as reverse osmosis and ion exchange, providing a solid foundation for ensuring the safe operation of subsequent equipment and achieving effluent quality standards.
