Tianjin University of Technology Separation Membrane Team Overcomes Membrane Scale-Up Barriers: Low-Energy High-Flux RO Membranes Now Operating Stably in 30+ Industrial Wastewater Projects

Recent coverage has highlighted the membrane-materials work of a team led by Professor Chang Na of the School of Chemical Engineering and Technology at Tianjin University of Technology, chief scientist of a National Key R&D Programme project. Working through the State Key Laboratory of Advanced Separation Membrane Materials, the team has spent more than a decade attacking the bottlenecks that keep separation membranes dependent on imports, moving results from laboratory samples into full industrial deployment.

China’s per-capita freshwater resources are only about a quarter of the world average, and its coastal industrial belt is both dense and water-intensive. Under national planning, China’s desalination capacity is to exceed 4.5 million cubic metres per day by 2030. Yet for a long time roughly 80% of the separation membranes used in domestic desalination plants above the 10,000 m3/d scale were imported. According to Chang, the initial rejection performance of domestic membrane materials is broadly comparable to imported products; the real gap lies in long-term stability against performance decay under continuous operation.

In 2023 the team was awarded the National Key R&D Programme project Low-Carbon, Energy-Efficient Seawater Desalination and Resource Recovery: Key Materials and Technology Demonstration. Working with an industrial partner in Shandong, the team manufactured domestic seawater RO membrane elements and installed them for offshore pilot testing. After three months of operation, however, the partner reported marked performance decay and a service life far shorter than comparable international products.

Through layer-by-layer forensics the team located the root cause. A seawater RO membrane is a three-layer composite: a non-woven backing for mechanical support, a polymer porous support layer, and an ultra-thin polyamide separation layer only 100–200 nm thick. The functional layer was not the problem. Instead, under sustained high-pressure compression of tens of kilograms in the operating vessel, pores in the porous support layer and the non-woven substrate were progressively crushed and densified, deforming the support structure irreversibly, constricting flow channels and degrading separation performance. The episode underlined the distance between ideal laboratory conditions and real industrial duty.

Another National Key R&D Programme project, Near-Zero Discharge and Resource Recovery of Printing and Dyeing Wastewater in High-Tech Zones, brought a different challenge. More than 30 parameters were checked one by one with no anomaly found, and no mature international precedent existed. The breakthrough came from an informal conversation with a veteran dyer who noted that acid, alkali and buffer solution are dosed as needed during dyeing. Targeted testing confirmed that sodium bicarbonate concentration had accumulated roughly tenfold in the recirculating reuse loop; because it is a buffer, pH readings barely moved, yet the accumulating salt steadily disturbed the dyeing reaction. After identifying the source, the team revised the treatment process and added a dedicated control step, and the demonstration project was successfully delivered.

A first batch of results is now moving into industrialisation:

• High-rejection seawater desalination RO membranes have completed long-term offshore pilot validation, advancing the push to break the dominance of imported high-end membranes;
• Low-energy, high-flux RO membranes are operating stably in more than 30 industrial wastewater treatment projects in multiple locations across China;
• A series of invention patents and new membrane fabrication processes have been licensed for commercialisation;
• The laboratory has established a technology-transfer platform in Cangzhou, Hebei, hosting pilot-scale testing and scale-up for water-security research outputs.

For the industrial water treatment sector, the findings carry direct practical value. Attributing domestic membrane decay under high-salinity, high-pressure continuous duty to collapse of the support layer gives membrane designers and plant engineers a verifiable improvement path, while the identification of accumulated buffer salts in the printing-and-dyeing near-zero-discharge demonstration offers a concrete lesson in monitoring and controlling recirculating industrial reuse systems.