Dual Stage Ultrafiltration Equipment for High Precision Water Treatment

Dual Stage Ultrafiltration Equipment for High Precision Water Treatment

Dual stage ultrafiltration equipment adopts two-stage serial membrane filtration structure to realize graded impurity removal for high-turbidity, high-pollution raw water in industrial production. As a high-precision graded industrial liquid filter with dual-layer interception protection, this dual-stage device can be combined with large-scale Industrial Skid Mounted Ultrafiltration Equipment, anti-fouling core Tubular Ultrafiltration Membrane, standard integrated Integrated Ultrafiltration Water Purification Equipment and consumable Ultrafiltration Membrane Filter to build hierarchical water purification systems adapting to severe raw water quality conditions. This paper comprehensively analyzes structural characteristics, staged filtration working mechanism, unified technical indicators, strict factory quality control standards and multi-industry application scenarios of dual stage ultrafiltration equipment, helping global industrial buyers solve the problem of easy membrane fouling of single-stage ultrafiltration equipment under poor raw water quality.

1. Product Introduction

Dual stage ultrafiltration equipment is an upgraded optimized product based on traditional single-stage ultrafiltration technology. The whole system is divided into primary coarse filtration stage and secondary fine filtration stage in series layout on an integrated stainless steel skid frame. The primary ultrafiltration unit intercepts most large particle suspended solids, large colloidal flocs and partial organic pollutants in raw water, while the secondary ultrafiltration unit performs deep fine filtration on the effluent from the first stage to thoroughly remove tiny colloids, bacteria, viruses and macromolecular organic matter, greatly reducing the pollution load borne by the secondary membrane components and prolonging the overall service life of membrane elements.

LEFILIER’s dual stage ultrafiltration equipment can freely match other mature products on the official website according to actual water quality conditions. For large sewage treatment stations with super high influent pollutant concentration, users can integrate dual-stage modules into combined Industrial Skid Mounted Ultrafiltration Equipment to realize large-flow graded water treatment. When the raw water contains oil sludge and high-concentration suspended solids, we install anti-blocking Tubular Ultrafiltration Membrane in the first-stage filtration cabin to improve the anti-fouling ability of the primary treatment unit. For medium and small enterprises that need quick installation and commissioning, the dual-stage structure is integrated into finished Integrated Ultrafiltration Water Purification Equipment, realizing plug-and-play delivery. Both primary and secondary filter cores of the dual-stage system adopt general Ultrafiltration Membrane Filter, which unifies the specification of spare parts and reduces the difficulty of later maintenance and replacement for customers.

The frame of dual stage ultrafiltration equipment is made of 304 stainless steel integral welding, with good corrosion resistance and structural stability. The default membrane material is modified PVDF hollow fiber membrane with strong oxidation resistance. The built-in PLC control system independently sets backwashing and chemical cleaning programs for the primary and secondary membrane modules respectively: the first-stage membrane with heavy pollution load is equipped with frequent backwashing logic, while the second-stage fine filtration membrane adopts low-frequency regular cleaning, realizing targeted maintenance for different membrane operation loads.

In the actual water treatment process, dual stage ultrafiltration equipment is mostly used as high-standard pretreatment equipment of reverse osmosis systems. It can stably control the SDI value of RO inlet water below 2.5, effectively avoid frequent fouling of reverse osmosis membranes caused by unqualified raw water pretreatment, and is widely used in pharmaceutical water preparation, electronics ultrapure water, high-purity beverage production and high-concentration industrial wastewater recycling projects.

2. Working Principle

The overall working principle of dual stage ultrafiltration equipment is pressure-driven cross-flow sieving, and the core advantage lies in graded pollutant interception through two series-connected membrane units. After raw water is boosted by the front-end feed pump to 1.0–4.0 bar working pressure, it first enters the primary ultrafiltration cavity for coarse filtration treatment.

Large-size suspended particles, large colloidal aggregates and partial high-molecular organic pollutants are intercepted on the surface of the first-stage membrane. Under the scouring of cross-flow water flow, most of the intercepted pollutants are discharged out of the system with primary concentrated water. The preliminarily purified water flows into the secondary ultrafiltration unit through the pipeline for deep fine filtration; tiny colloidal particles, microorganisms, viruses and residual small molecular organic pollutants are completely trapped by the secondary membrane layer, and the finally produced qualified clean permeate water is transported to the clean water tank.

Two independent maintenance mechanisms are set for the primary and secondary membrane groups in the program of dual stage ultrafiltration equipment. First is differential pressure + timing dual-trigger automatic backwashing: the primary membrane with heavy pollution load is set with a shorter backwash interval, and the secondary fine filter membrane adopts a longer backwash cycle to save water consumption. Second is segmented CIP chemical cleaning: the primary membrane is cleaned with alkaline medicament preferentially to decompose a large amount of organic dirt, while the secondary membrane is matched with mixed acid-base cleaning liquid to remove residual trace scale and biological film. If the primary unit is equipped with tubular membrane elements, online sponge ball physical cleaning can be added to further reduce the organic fouling degree of the first-stage membrane surface.

3. Technical Parameters 

3.1 Matching Membrane Parameters for Dual Stage Structure

1. Standard membrane material: Modified industrial PVDF; food-grade PES optional for pharmaceutical & food industries

2. MWCO configuration matching: Primary stage 100 kDa (coarse filtration); Secondary stage 30/50 kDa (fine filtration)

3. Membrane pore size range: 0.01~0.1μm

4. Allowable operating temperature: 5℃ ~ 45℃ continuous operation

5. pH tolerance: Continuous running pH 2–11; cleaning tolerance pH 1–13

6. Design flux: Primary stage 30~85 LMH; Secondary stage 20~60 LMH

3.2 Whole Dual Stage Equipment Operating Index

1. Optimal overall working pressure: 1.6 ~ 3.2 bar

2. Total system water recovery rate: 80% ~ 91%

3. Final effluent turbidity: Steadily less than 0.05 NTU

4. Total bacteria interception rate: ≥99.999%

5. Outlet water SDI value: ≤2.5, higher than the pretreatment standard of ordinary single-stage ultrafiltration

3.3 Equipment Hardware Configuration Parameters

1. Frame material: 304 stainless steel integrated skid frame

2. Control system: PLC + touch screen independent program control for two stages, with fault alarm function

3. Primary backwash cycle: 15–40 min adjustable; Secondary backwash cycle: 30–60 min adjustable

4. Recommended overall chemical cleaning cycle: 1.5 ~ 5 months

5. Customizable water production capacity: 1T/h, 5T/h, 15T/h, 50T/h, 100T/h standard specifications

4. Product Quality & Manufacturing Standards

Every set of dual stage ultrafiltration equipment produced by LEFILIER implements full-process quality monitoring from membrane incoming inspection to finished product delivery. Before assembly, each batch of primary and secondary Ultrafiltration Membrane Filter must pass the bubble point integrity test one by one to screen out defective products such as fiber fracture and membrane leakage, ensuring graded interception precision of the two-stage system.

Stainless steel frame welding and internal segmented pipelines adopt precision argon arc welding technology, all water-wetted materials are anti-corrosion and harmless materials to prevent secondary pollution of water quality. After assembly, each dual-stage equipment must pass FAT factory acceptance test: simulate high-turbidity raw water working conditions to test staged water yield, pressure difference changes and independent backwash program execution effect, and deliver products only after all test indicators are qualified.

Our dual stage ultrafiltration equipment has passed ISO9001 quality certification, CE safety certification and NSF61 drinking water material certification. Under standardized operation and segmented maintenance, the service life of the first-stage PVDF membrane is 5–7 years, and the service life of the secondary fine filtration membrane can reach 6–8 years, effectively reducing the overall membrane replacement frequency and long-term operating costs for enterprises. Each equipment is equipped with complete operation manual and quality inspection report for after-sales traceability.

5. Application Fields

Relying on graded filtration, low membrane fouling rate and high effluent precision, dual stage ultrafiltration equipment is widely used in high-standard water treatment scenarios:

1. Electronic industry ultrapure water pretreatment: Deeply purify raw water to ensure stable inlet water quality for EDI and reverse osmosis systems

2. Pharmaceutical purified water preparation: Double interception removes pyrogen, endotoxin and microorganisms to meet pharmaceutical water standards

3. High-purity beverage & dairy production water treatment: Eliminate trace impurities while retaining beneficial natural substances in water

4. High-turbidity surface water purification: Treat reservoir water, river water with high sediment content for factory production water supply

5. High-concentration biochemical wastewater advanced treatment: Reduce pollutant load step by step to improve wastewater reuse rate

6. Cosmetic production water preparation: Meet high cleanliness requirements of cosmetic process water through two-stage precise filtration

FAQ 

Q1: What core advantages does dual stage ultrafiltration equipment have compared with conventional single-stage ultrafiltration?

A: Dual-stage structure undertakes pollutant interception in grades, the first stage bears most dirt load to protect the secondary fine filter membrane, effectively slowing down membrane fouling speed, prolonging membrane service life and obtaining higher-purity stable effluent water quality.

Q2: Can dual stage ultrafiltration equipment remove dissolved salt ions and reduce water TDS value?

A: Ultrafiltration only intercepts particulate matter, colloids and microorganisms, salt ions can freely pass through membrane pores. If desalination is needed, this dual-stage equipment must be matched with reverse osmosis equipment as front-end pretreatment.

Q3: Is the maintenance cycle of the two groups of membranes in dual stage ultrafiltration equipment consistent?

A: Inconsistent. The primary membrane contacts high-pollution raw water with a shorter backwash and cleaning cycle; the secondary membrane has low pollution load with a longer maintenance period, and the system independently sets operating parameters for the two stages.

Q4: Can I modify an existing single-stage ultrafiltration device into dual stage ultrafiltration equipment?

A: Direct reconstruction is not recommended, because dual-stage equipment needs matched graded pipeline layout and dual independent control programs. It is more stable to purchase integrated finished dual-stage ultrafiltration equipment according to actual water volume.

Q5: Does dual stage ultrafiltration equipment consume more water and electricity than single-stage products?

A: Although there is slight power consumption increase, the membrane cleaning frequency is greatly reduced, and the overall water consumption for cleaning is lower than single-stage equipment with frequent pollution blockage, so the comprehensive operating cost is more economical in long-term operation.

Q6: What kind of raw water quality is most suitable for using dual stage ultrafiltration equipment?

A: It is suitable for raw water with high turbidity, high suspended solids, high organic content and raw water that is easy to cause frequent fouling of ordinary single-stage ultrafiltration membranes, such as river water, biochemical wastewater and raw water for pharmaceutical production.

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