In water treatment, commonly used filtering clarifier or sedimentation water, filtered water turbidity to make to meet the water requirements; In the process, the filter constant as adsorption, ion exchange, membrane separation method preprocessing means; As the depth of processing biological treatment, water reuse requirements reach after filter.
Filter mechanism can be divided into resistance interception, gravity sedimentation and flocculation contacting three. When the flow through the layer, the larger particle size of suspended particles are trapped in the surface layer of the first gap, so that the gap between the layer of smaller, interception capability are becoming increasingly high. Results gradually form a layer mainly composed of solid particles trapped constituted by filtering it plays a major role. This role belongs to the resistance or rejection sieve effect. When the filter layer through the filter media surface provides numerous huge size of the settlement. It is estimated that, 1m3 diameter of 0.5mm in the media is not to have a 400m2 area of water erosion and for effective settlement of suspended solids, formed countless small ”, suspended solids settle here easily. Gravity sedimentation intensity depends on the diameter of the filter and filtration rate. The smaller the filter, the greater the size of the settlement; filtration rate, the smaller the more stable flow, which are conducive to the settlement of suspended solids. Since the filter has a large surface area, there are obvious physical adsorption between it and suspended solids. In addition, sand the surface of the water, often with a negative charge, can absorb iron and aluminum with positively charged colloid, thereby positively charged film formed on the surface of the filter, which in turn adsorb negatively charged clay and a variety of organic colloids on sand brought into contact flocculation. In most cases, the filter surface has not yet been aggregated colloid can also play the role of intermediary contact impact and promote its aggregation process.