Membrane Filters

In water treatment, hollow fiber ultrafiltration membranes, with their unique structure and performance, offer multiple advantages:

1. High filtration precision, reliable purification results

The membrane pore size is typically 0.001-0.1μm, effectively intercepting impurities such as bacteria, viruses, colloids, large organic molecules, and suspended solids in water, while retaining beneficial minerals (such as calcium and magnesium ions). The resulting filtered water is crystal clear, directly meeting basic purification needs for drinking water, industrial process water, and other applications.

Case: After being used by a municipal water plant, the turbidity of raw water dropped to below 0.1NTU, and the bacteria removal rate was as high as 99.9%.

2. High Flux and Efficiency

The hollow fiber structure significantly increases the membrane's specific surface area (effective filtration area per unit volume), resulting in higher filtration flux for the same volume. This allows for rapid treatment of large volumes of water, making it suitable for large-scale water treatment applications (such as municipal and industrial wastewater treatment).

Case: In a wastewater treatment project in an industrial park, the average daily processing capacity of a single membrane module reached 5,000 m³, meeting the reclaimed water reuse needs of approximately 3,000 people.

3.Low operating costs and excellent energy efficiency

The filtration process requires only a low operating pressure (typically 0.1-0.3 MPa), resulting in significantly lower energy consumption than deep filtration technologies such as reverse osmosis. Furthermore, the membrane modules can be restored through backwashing and chemical cleaning, extending their service life (typically 3-5 years) and reducing replacement costs.

4.Strong anti-pollution ability and wide adaptability

Some materials (such as PVDF membranes) are resistant to acid, alkali, and oxidation, and can withstand complex water conditions (such as highly polluted industrial wastewater and high-salinity environments). Processes such as cross-flow filtration can reduce the deposition of pollutants on the membrane surface, slowing membrane fouling and maintaining stable operation.

5. Flexible Application Scenario and Strong Compatibility

It can be used independently as a deep filtration unit or in combination with other processes (such as pretreatment, reverse osmosis, and nanofiltration). It is highly compatible with a variety of scenarios, including drinking water purification, wastewater treatment and reuse, and industrial purification.

Ultrafiltration(UF) is a process that uses a membrane with a pore size of 0.001-0.1 microns to filter solutions containing macromolecules or fine particles under pressure, separating them from the solution. It has a high removal rate for suspended solids, colloids, macromolecules, and bacteria in water.

Ultrafiltration membranes primarily operate on a screening mechanism, falling between microfiltration and nanofiltration. Water purification is determined by operating pressure and membrane pore size. In some material separation systems, membranes with different pore sizes can selectively separate specific products. Due to their small pore size, they are primarily used to remove suspended solids, colloids, microorganisms, macromolecules, bacteria, and viruses from aqueous solutions.

Cleaning and Maintenance Operations for Hollow Fiber Ultrafiltration Membranes

The cleaning and maintenance of hollow fiber ultrafiltration membranes require selecting appropriate methods based on the degree of contamination, mainly including daily maintenance, physical cleaning, and chemical cleaning. The specific steps are as follows:

I. Daily Maintenance (Pollution Prevention)

1. Regular backwashing

- Operation: Close the product water valve, open the backwash inlet valve and concentrate discharge valve. Use filtered water (or product water) to rinse the membrane surface in reverse, with a flow rate 1.2-1.5 times the normal product water flow rate, lasting 3-5 minutes.

- Frequency: Generally once every 1-4 hours of operation, depending on operating conditions.

2. Timely air exhaust

- Air trapped in membrane modules can exacerbate local concentration polarization and pollution. Regularly open the exhaust valve to release air, especially during initial startup.

II. Physical Cleaning (Removing Loose Surface Contaminants)

Suitable for mild pollution (e.g., attached suspended solids, colloids).

1. Forward flushing 

- Close the concentrate valve, increase the inlet flow rate (1.5-2 times the normal product water flow), open the product water valve and排污阀 (sewage valve), and flush for 5-10 minutes to remove surface contaminants with water flow.

2. Air-water mixed cleaning

- If the system design allows, inject compressed air (pressure 0.1-0.2MPa) while backwashing. The air-to-water ratio is approximately 5:1, lasting 3-5 minutes. Bubbles oscillate to peel off contaminants.

III. Chemical Cleaning (Removing Stubborn Contaminants)

Use when physical cleaning is ineffective (e.g., product water flow drops by >15%, pressure difference rises by >20%). Select agents based on contaminant type:

1. For organic pollution

- Agent: 0.5-1% NaOH solution (or with a small amount of surfactant).

- Operation: Inject the agent into the membrane module, soak for 30-60 minutes (or circulate for 1-2 hours), then rinse with clean water until pH is neutral.

2. For inorganic pollution (e.g., calcium-magnesium scale, iron-manganese scale)

- Agent: 0.5-2% hydrochloric acid (or citric acid/oxalic acid solution, 1-3% concentration).

- Operation: Circulate or soak for 30-60 minutes, then rinse with clean water until pH is neutral (avoid residual acid corroding the membrane).

3. For microbial pollution

- Agent: 0.1-0.2% sodium hypochlorite solution (based on available chlorine concentration).

- Operation: Circulate for 20-30 minutes or soak for 1-2 hours, then rinse with clean water until no residual chlorine remains (check with chlorine test strips).

4. Notes

- Frequency: Generally once every 3-6 months, adjusted based on pollution levels.

- Avoid agents harmful to the membrane material (e.g., excessive chlorine may damage PVDF membranes; confirm the membrane's tolerance range in advance).

IV. Post-Cleaning Inspection and Maintenance

- After cleaning, start the system and check parameters such as product water flow, water quality, and pressure difference to ensure they return to normal ranges.

- For long-term shutdown (over 1 week), soak the membrane module in a protective solution (e.g., 0.5% sodium bisulfite solution) to prevent microbial growth and membrane drying.

These operations effectively extend the service life of hollow fiber ultrafiltration membranes and maintain stable filtration performance. Strictly control flow rate, pressure, and chemical concentration during operation to avoid damaging the membrane structure.

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