Multi-Media Water Filter: Detailed Explanation

 Filtration Process and Media

 A multi-media water filter utilizes one or several types of filter media to pass high-turbidity water through a specified thickness of granular or non-granular materials. This process effectively removes suspended impurities and clarifies the water. Common filter materials include quartz sand, anthracite, and manganese sand. This method is primarily used for:

 · Turbidity Removal

· Water Softening

· Pre-treatment for Pure Water Production

 The effluent turbidity can be reduced to below 3 NTU (Nephelometric Turbidity Units).

 

Applications in Industrial Water Treatment

 Multi-media filters are crucial in industrial circulating water treatment systems, where they:

 · Remove Impurities and Adsorb Oil: Ensuring the water quality meets recycling standards.

· Remove Suspended or Colloidal Impurities: Particularly effective for tiny particles and bacteria that precipitation technology cannot remove.

· BOD5 and COD Reduction: Contributing to the reduction of biochemical oxygen demand (BOD5) and chemical oxygen demand (COD).

· Protect Reverse Osmosis Membranes: Reducing mechanical damage and pollution to membrane elements.

 

Components of a Multi-Media Filter

1. Supporting Pipelines and Valves

2. Filter Body:

· Cylinder

· Backwash Air Pipe

· Water Distribution Component

· Support Component

· Filter Material

· Exhaust Valve (External)

 

Inner Filter Layer Composition

 The filter media are arranged in the filter tank based on their specific gravity and particle size:

· Upper Layer: Anthracite with small specific gravity and larger particle size.

· Middle Layer: Quartz sand with moderate specific gravity and smaller particle size.

· Lower Layer: Gravel with larger specific gravity and larger particle size.

 This arrangement prevents chaotic layering during backwashing, ensuring the filter media's retention capacity.

 

Quartz Sand Filter

 Quartz sand filters are designed to effectively remove suspended matter, colloids, iron, organic matter, pesticides, manganese, bacteria, viruses, and other pollutants from water. Key advantages include:

 · Low Filtration Resistance

 · Large Specific Surface Area

 · Strong Acid and Alkali Resistance

 · Oxidation Resistance

 · Wide pH Range (2-13)

 · Good Pollution Resistance

 · Simple Structure

 · Automatic Operation

 · Large Flow Rate

 · Few Backflushing Times

 · High Filtration Efficiency

 · Low Resistance

 · Convenient Operation and Maintenance

The unique design allows adaptive operation, automatically forming an upper and lower dense state during filtration, ensuring consistent effluent quality under various conditions. The filter material disperses fully during backwashing, ensuring effective cleaning.

 

Multi-Media Filter Media Stratification

 Multi-media filters typically use three layers of media:

  1. Anthracite: Lightest, largest particles, stratifies at the top.

 2. Sand: Intermediate density and particle size, settles in the middle.

 3. Garnet: Heaviest, smallest particles, settles at the bottom.

This stratification ensures that the largest contaminants are trapped in the top layer, with smaller particulates filtering down into the lower layers. This method allows for more efficient turbidity removal and longer run times between backwash cycles. Multi-media filters can remove particles down to 10-25 microns, compared to 25-50 microns for simple sand filters.

 

Backwashing and Maintenance

Operating at higher pressure differentials can drive particles deep into the media bed, making them difficult to remove during backwashing. Over time, this can lead to shortened filter runs and high differential pressures. To address this:

 · Air Scour: Helps loosen packed dirt in the media bed.

 · Drain Down Period: Precedes air scour in the backwash cycle to bleed water out of the filter vessel.

  

 Use of Flocculants/Coagulants

Flocculants or coagulants can be used upstream of the filter to induce tiny dirt particles to agglomerate, forming larger particles that the filter can more easily remove. This process, called "agglomeration," with proper

 

Multi-Media Water Filter: Advantages and Applications

Enhanced Filtration Efficiency

 Unlike traditional sand filters, multi-media water filters are composed of three distinct filtration media, ordered in decreasing porosity. This multi-layer design allows these filters to trap and retain a significantly larger number of particles before backwashing becomes necessary. The key benefits include:

· Extended Operational Periods: By trapping sediment and particulates throughout the entire depth of the filter bed, multi-media water filters can operate for much longer periods compared to conventional sand filters.

· High-Quality Output: The process of multimedia filtration produces high-quality, filtered water at much faster flow rates than traditional sand filtration.

These features make quartz sand filters highly efficient and easy to manage.

Working Principle

The working principle of the multi-media filter involves the following steps:

 1. Reverse Water Flow: The water flows reversely through the filter layer, causing it to expand and suspend.

 2. Cleaning Mechanism: The filter layer is cleaned by the shear force of the water flow and the collision and friction of the particles, which removes the dirt.

3. Backwash: The dirt is then discharged along with the backwash water.

  Applications of Multi-Media Filters

 Multi-media filters are versatile and can be applied in various settings, including:

 Pretreatment Systems:

· Reverse Osmosis

· Electrodialysis

· Ion Exchanger

· Ultrafiltration

Industrial Pre-Filtration:

· Raw water treatment for power generation, chemical industry, paper making, beverages, etc.

Water Supply Treatment:

· Decolorization and organic removal in chemical plants

Domestic Water Pretreatment

Industrial Water Treatment

Swimming Pool Water Treatment

Circulating Water Side Filter Systems

Surface and Groundwater Treatment:

· Reducing turbidity and discoloration

Waste Water Treatment

 

Conclusion

Multi-media water filters offer superior filtration efficiency, extended operational periods, and high-quality water output compared to traditional sand filters. Their multi-layer design, combined with the advantages of quartz sand filters, makes them ideal for a wide range of applications, from industrial pre-filtration to domestic water treatment. The ability to trap and retain particles throughout the entire depth of the filter bed ensures that these filters can operate efficiently for longer periods, reducing the frequency of backwashing and maintenance.

 

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