Ultrafiltration Membrane Cleaning and Maintenance Methods

1. Chemical Cleaning

Chemical cleaning essentially involves the use of chemical reagents to remove contaminants from membranes by reacting with deposits, fouling, corrosion products, and other pollutants that affect flux rates and product water quality. These reagents include acids, alkalis, chelating agents, oxidants, and formulated products.

‌1.1 Acid and Alkali Solutions

Acids are effective in removing calcium-based scales (e.g., calcium carbonate, calcium phosphate), iron oxides, and metal sulfides. Alkaline cleaning solutions, such as phosphates, carbonates, and hydroxides, loosen, emulsify, and disperse deposits. Surfactants are often added to alkaline cleaners to enhance their detergency for removing wetting oils, grease, dirt, and biological materials. For particularly stubborn deposits like silicates, alternating between alkaline and acidic cleaners is recommended, with an optimal pH range of 3–11.

‌1.2 Chelating Agents

In addition to strong acids and alkalis, chelating agents are used to remove deposits from fouled membranes. Common chelators include ethylenediaminetetraacetic acid (EDTA), phosphonocarboxylic acids, gluconic acid, and citric acid. Gluconic acid is particularly effective for chelating iron ions in strongly alkaline solutions, while EDTA is often used to dissolve alkaline earth metal sulfates.

1.3 Oxidizing Agents

When NaOH or surfactants are ineffective, chlorine (sodium hypochlorite, 0.2–0.5%) can be used for cleaning, with an optimal pH range of 10–11.

2. Cleaning

Ultrafiltration (UF) membrane fouling refers to the irreversible changes in water flux and separation characteristics caused by physicochemical interactions between microorganisms, colloidal particles, solute molecules, and the membrane; concentration polarization leading to solute precipitation on the membrane surface or within pores; or mechanical factors causing adsorption or blockage.

When UF membranes require cleaning, ‌Chongqing Jiahe Filtration Technology Co., Ltd.‌ recommends analyzing the nature and composition of the pollutants to select an effective cleaning method. Common approaches include physical, chemical, or combined physical-chemical methods.

‌Physical Cleaning‌ The most common physical method is hydraulic flushing, which includes equal-pressure flushing (no pressure difference across the membrane) and backflushing (with a pressure difference). Generally, backflushing is more effective.

苏州苏尔科环保工程有限公司的化学清洗法是采用化学清洗剂清洗。因污染的性质而异可分为：酸性清洗剂、碱性清洗剂、氧化性清洗剂和生物酶清洗剂等。 酸性清洗剂常用：0.1mol/L HCL、0.1mol/L 草酸、1%～3%柠檬酸、1%～3%柠檬酸铵、EDTA等，这类清洗剂对去除Ca2+ 、Mg2+ 、Fe3+ 等金属盐类及氢氧化物、无机盐凝胶层是较为有效的。

‌Alkaline cleaners‌: 0.1–0.5% NaOH solution, effective for lipid-based contaminants.

‌Oxidizing cleaners‌: 1.0–0.5% H₂O₂, 0.5–1.0% NaClO, 0.05–0.1% sodium azide, etc., which work well for organic fouling.

‌Bioenzyme agents‌: 1% pepsin, trypsin, etc., effective for protein, polysaccharide, and lipid contaminants. Optimal results are achieved at 55–60°C, but membrane temperature tolerance must be considered.

苏州苏尔科环保工程有限公司超滤膜的清洗步骤如下可供参考：

（1）Rinse the entire UF system with clean water, preferably at the highest temperature the membrane can tolerate.

（2）Circulate a suitable cleaning agent (containing EDTA or sodium hexametaphosphate as needed).

（3）Rinse with clean water to remove residual cleaning agents.

（4）Verify the membrane’s water flux under specified conditions. Repeat steps 2–3 if the target flux is not achieved.

（5）Soak and store the membrane in a 0.5% formaldehyde, sodium bisulfite, or alkaline (0.3–0.5%) solution for disinfection.

苏州苏尔科环保工程有限公司关于膜的保存建议：
During system shutdown, membranes must be preserved to prevent bacterial growth. They can be stored either within the system or after disassembly.
In-System Storage (Short-Term, <1 Month)‌:
1）Clean the membrane using the onsite CIP (Cleaning-in-Place) system.
2）Fill the system with a 0.5–1% sodium bisulfite (food-grade) preservation solution to immerse the membranes.

3）Maintain the solution’s pH between 3.5–9.5. Monitor regularly; replace the solution if pH deviates.
4）Monitor bisulfite concentration. Replace if it drops below 0.1%.
5）Store below 25°C.

Post-Disassembly Storage (Long-Term, >1 Month)‌:
1）Clean the membrane via CIP.
2）Disassemble and drain the membrane.
3）Immerse the membrane in a solution of 1% sodium bisulfite (food-grade) and 18% propylene glycol for 30 minutes. Monitor and adjust concentration as needed.
‌Note‌: Disassembly is not advised unless necessary. Consult the company’s technical team before disassembly.

4）Drain the membrane, seal it in a dry plastic bag (without residual solution)
5）and store in a cool, dry place (10–20°C). Refrigeration is recommended.