Multi-Media Filter Structure Design and Combined Processes

Multi-media filters are an efficient water treatment technology. They play a crucial role in solving water pollution problems. The unique structure of these filters, which use multiple layers of filtering materials, provides precise purification for different types of water pollutants. The filter media are typically a combination of quartz sand, anthracite, manganese sand, and other materials. Each layer of filter media has different particle sizes and filtration functions. This enables the effective removal of suspended solids, impurities, and fine pollutants. This article will discuss the structural design principles of multi-media filters, the selection of filter media, common combined processes, and their applications in different water treatments.

Structure Design of Multi-Media Filters

The filter media in a multi-media filter typically consist of quartz sand, anthracite, manganese sand, and other materials. Different filter layers are designed to perform graded filtration of various pollutants in the water. A common example is the multi-porous plate structure. The typical design includes:

1. Filter Media Layers

Bottom Layer: Quartz Sand

Quartz sand is the primary filter media and is usually placed at the bottom of the filter bed. Quartz sand has a larger particle size (2-4mm) and is mainly used to remove larger suspended particles from the water. The thickness of the bottom quartz sand layer is usually about 200mm.

Upper Layer: Anthracite

Anthracite is often used in the upper layer, especially when dealing with oily water sources. Anthracite can effectively adsorb oils from the water. The carbon content of anthracite is an important indicator of its quality, typically ranging from 30% to 90%. The higher the carbon content, the better the filtration efficiency. The particle size of anthracite generally ranges from 1-2mm, and the thickness of this layer is about 400mm.

Middle Layer: Quartz Sand Filtration Layer

The quartz sand filtration layer typically consists of sand with a particle size between 0.5 and 1.0mm. The thickness of this layer is about 600mm. This layer further removes smaller suspended solids and impurities.

2. Structural Characteristics

The height of the cylindrical section of the multi-media filter is typically around 2000mm, with the filler height ranging from 1000mm to 1200mm. If anthracite is used, its thickness is 400mm. The quartz sand layer is typically about 800mm (200mm cushion + 600mm filtration layer).

In the design process, it is essential to ensure that the particle size of the filter media increases gradually from the bottom to the top. This allows the upper layers to perform coarse filtration, while the lower layers handle fine filtration. This design ensures that after backwashing, the filter bed retains its stratification. This avoids the mixing of filter media and helps maintain stable and continuous filtration performance.

Common Combined Processes for Multi-Media Filters

Depending on the water quality requirements and treatment stages, common combined processes for multi-media filters are as follows.

1. Pre-Treatment Stage

Coagulation and Sedimentation + Multi-Media Filtration: In the pre-treatment stage, coagulants and flocculants are used to aggregate suspended solids and colloids into larger particles. These particles are then removed through a sedimentation tank. The water is then passed through the multi-media filter to further remove remaining suspended solids and fine particles, improving water quality.

Sand Filtration + Multi-Media Filtration: In some water treatment systems, sand filters are used to remove larger particles before entering the multi-media filter for deeper purification. This combined process is effective in situations where there is a higher concentration of particles in the water, improving the effluent quality.

2. Deep Treatment Stage

Multi-Media Filtration + Activated Carbon Adsorption: After multi-media filtration removes most suspended solids, water passes through an activated carbon filter. The activated carbon effectively adsorbs organic substances, colorants, and odors in the water. This process is widely used for drinking water and industrial wastewater treatment, especially when trace organic contaminants need to be removed.

Multi-Media Filtration + Softening Treatment: For hard water, multi-media filtration removes impurities, followed by ion exchange resin softening to reduce water hardness. This process is commonly used in drinking water treatment and boiler feedwater softening.

3. Advanced Treatment and Purification Stage

Multi-Media Filtration + Reverse Osmosis (RO): Multi-media filtration is used before reverse osmosis to remove particles and suspended solids. This helps prevent contamination and blockage of the RO membrane. The combined process extends the life of the RO system and ensures stable operation.

Multi-Media Filtration + Ultrafiltration (UF): Before ultrafiltration, multi-media filtration removes larger particles to protect the ultrafiltration membrane and reduce membrane fouling. Ultrafiltration removes finer particles, bacteria, and viruses. It is widely used in water purification, the food industry, and pharmaceutical applications.

4. Special Treatment Needs

Multi-Media Filtration + Manganese Sand/Manganese Iron Sand Filtration
Manganese sand or manganese iron sand effectively removes iron and manganese ions from water. This process is especially suitable for water sources with high iron and manganese content.
Multi-Media Filtration + Resin Softening + Disinfection
This combined process is used for drinking water or industrial water treatment. After multi-media filtration removes impurities, resin softening reduces water hardness. Finally, disinfection using chlorine or ultraviolet light ensures the water meets safety standards.

5. Selection of Combined Processes

The combination processes for multi-media filters should be designed and selected according to the raw water characteristics, treatment objectives, and final usage (such as drinking water, industrial cooling water, or boiler feedwater). The sequence and configuration of processes can be adjusted to achieve cost-effective water quality purification that meets relevant standards. Proper selection of combined processes improves water treatment efficiency, extends equipment lifespan, and ensures stable system operation.

Conclusion

Multi-media filters are an efficient water treatment technology. With their excellent layered filtration design and combination of various media, they effectively solve a wide range of water quality issues. By using reasonable structural design and flexible process combinations, multi-media filters provide reliable solutions for different water treatment needs. As water treatment technology continues to develop and water quality requirements increase, multi-media filters will play a more important role in various fields. They will help achieve sustainable water resource use and contribute to environmental protection goals.