ZSL type medium-speed filter

• Product Overview

The medium-speed filter is a granular media deep filtration system designed and manufactured by our company for water treatment processes. Typically using single-layer quartz sand or anthracite as the filtration medium, this equipment effectively removes suspended solids, colloids, silt, and certain organic compounds from water through moderate filtration flow rates, thereby reducing turbidity and purifying water quality. It strikes a balance between filtration efficiency, operational lifespan, and space requirements, making it a common filtration unit in municipal water supply, industrial water treatment, and advanced wastewater processing.

• Structure and Working Principle

1. Core structural composition

The device is a vertical cylindrical steel pressure vessel, with a core structure similar to that of a conventional mechanical filter, primarily comprising:

• Tank body: The main pressure-bearing structure, typically constructed from corrosion-resistant carbon steel, stainless steel, or fiberglass reinforced plastic (FRP).
• Single-layer filter media: The core filter layer, typically composed of homogeneous quartz sand, and occasionally anthracite. The filter media particle size is strictly sieved, and the layer height is designed and calculated.
• Water distribution and collection system:

• Upper water distribution device: ensures uniform water distribution across the filter layer surface to prevent erosion.
• Bottom water collection/distribution device: Collects clean water during filtration and evenly distributes rinse water and air during backwashing. The common form is a porous plate system composed of filter plates, filter caps, or filter heads.
  • Pipeline and valve system: Enables process switching including filtration, backwashing, and forward washing, with manual or automatic control.
  • Monitoring device: Inlet and outlet pressure gauges or differential pressure gauges, used to monitor the resistance of the filter layer.

2. Working Principle

The equipment runs in the cycle of filtration and backwash periodically.

• Filtration process: Under pressure, the raw water permeates through the entire filter media layer from top to bottom. Impurities in the water are progressively retained through mechanical sieving, adsorption, and sedimentation. The effluent is collected by the bottom water collection system.
• Backwashing process: When the filter layer reaches saturation with retained contaminants, the pressure drop exceeds the set threshold or the effluent quality deteriorates, backwashing is initiated. This is performed using either water backwashing or a more efficient air-water combined backwashing method. The process involves high-speed upward flushing of the filter media, causing it to expand, tumble, and detach retained contaminants, thereby restoring the filter's filtration performance.
• Core technical features

1. Balanced operational parameters: The designed filtration velocity (typically 8-12 m/h) falls between slow and high-speed filters, ensuring adequate filtration efficiency while maintaining compact footprint and optimal operational cycles.
2. The filtration performance is relatively stable: homogeneous or properly graded single-layer filter media, combined with a uniform water and gas distribution system, helps achieve consistent filtration results, with effluent turbidity typically maintained at low levels.
3. Key to backwashing efficacy: High-efficiency air-water combined backwashing technology is particularly crucial for restoring the performance of medium-speed filters. Air scrubbing effectively breaks down sludge balls, while water flushing discharges them, thereby maintaining the long-term cleanliness and filtration capacity of the filter media.
4. The operation management is mature: As a classic filtration process, its operating procedures are well-established, enabling easy automation control, and daily maintenance is relatively standardized and straightforward.
5. Extensive applicability: It can function as an independent filtration unit or serve as a reliable pre-filtration security filter for membrane treatment systems (e.g., ultrafiltration, reverse osmosis), with broad adaptability to diverse water quality conditions.

• Main technical parameters

• Typical Application Fields

This filter is suitable for various water treatment scenarios with specific turbidity requirements for the effluent.

• Municipal water treatment: As a filtering unit in the conventional treatment process of urban water plants, it is the key link to ensure that the turbidity of drinking water meets the standards.
• Pre-treatment and filtration of boiler feed water, circulating cooling water and process water to meet the turbidity requirements of the system.
• Advanced Wastewater Treatment and Reuse: In tertiary wastewater treatment or reclaimed water processes, this technology is employed to further remove suspended solids from secondary effluent, ensuring stable operation of subsequent disinfection or membrane treatment processes.
• Seawater desalination pretreatment: As a critical protective step before reverse osmosis systems, it reduces influent turbidity and the Standard Desalination Index (SDI).
• Landscape water and circulating water treatment: Used for filtration and purification of landscape water bodies and swimming pool circulating water in parks and communities.