Sand Filter
In the textile dyeing wastewater treatment process, the sand filter (typically a multi-media filter) serves as a pivotal transitional and safeguarding component, bridging physicochemical pretreatment with advanced treatment/reuse. Its core function is to achieve deep interception and stabilize water quality, thereby ensuring a reliable feed water supply for subsequent precise membrane treatment or advanced oxidation processes.
Working Principle
The working principle involves using filter media of different particle sizes and densities (anthracite, quartz sand, garnet, etc.) to form a multi-layered filter bed. Through gradient filtration from coarse to fine, flowing from top to bottom, it mechanically intercepts, adsorbs, and deeply filters residual pollutants in the water stream.
Design & Operational Features
Filtration Precision Selection
Filtration precision of 1–10 micrometers is typically selected based on protected system. UF protection uses 50–100μm; RO protection requires 1–5μm precision.
Chemical Resistant Media
Filter media materials (PP, PES) must exhibit good chemical compatibility to resist residual oxidants, acids, and alkalis in printing and dyeing wastewater.
Low-Turbidity with Fine Particles
Influent is clarified water from sedimentation, sand filtration, etc., yet contains micrometer-sized fiber flocs, activated carbon powder, biological debris, and colloids difficult to remove by conventional filtration.
Pressure Differential Control
Monitor inlet-outlet pressure differential. A significant increase (typically 0.05–0.1 MPa) indicates filter clogging, requiring timely replacement to establish regular maintenance schedule.
Multimedia Filter Application Scenarios
Standard Filtration After Physicochemical Treatment
Positioned after coagulation sedimentation/flotation and before activated carbon adsorption / precision filtration / membrane systems. An essential standard unit in water reuse treatment lines.
Purification After Biological Effluent
Used for advanced purification of effluent following biological treatment (aerobic processes), removing particulate COD and biological debris to prepare for subsequent decolorization or desalination.
Side-Stream Filtration for Cooling Water
Applied to treat recirculating cooling water in textile dyeing plants, removing microbial slime and particulate matter to maintain heat exchange efficiency.
Core Pre-treatment for Membrane Systems
Positioned ahead of reverse osmosis (RO) systems. Together with activated carbon filters and precision filters, forms the "three-stage pre-treatment" — the core coarse filtration and safeguarding component.
Core Advantages
01
Stable Operation & Shock Load Resistance
Multi-layer filter bed structure enables handling of short-term fluctuations in effluent quality from upstream physicochemical treatment units.
02
Reliable Treatment & Significant Water Quality Improvement
Consistently maintains effluent turbidity below 3 NTU or even lower, substantially reducing treatment burden on downstream units.
03
Low Operational & Maintenance Costs
Filter media have long lifespan (3–5 years or longer). Primary operational costs are water and energy for backwashing, ensuring high cost-effectiveness.
04
Easy Management & High Automation
Fully automatic control valve systems enable automatic backwashing based on pressure differentials or timed intervals, minimizing manual operation.
The sand filter plays the role of a "deep purifier" and "system stabilizer," bridging the preceding and following processes. Through reliable physical filtration, it performs the final interception of suspended and colloidal pollutants not fully removed in earlier treatment stages. As a foundational equipment, it ensures the long-term stable operation of downstream advanced treatment processes (especially membrane systems), reduces overall operational and maintenance costs, and enhances the reliability of the entire system. Its operational status directly determines the success of the pretreatment phase in water reuse systems.