The research on seawater desalination at the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of the Chinese Academy of Sciences (CAS) was recently highlighted by Asian Scientist, after the progress news was posted on the CAS website.  

Towards Zero-Discharge Seawater Desalination (Asian Scientist) 

Chinese researchers have developed a novel process that can produce pure drinking water without the highly concentrated waste products. 

Asian Scientist Newsroom | November 18, 2016 | In the Lab  

AsianScientist (Nov. 18, 2016) - Researchers in China have developed a method of salt water desalination that generates very little waste and is less susceptible to scaling. Their results have been published in the Journal of Membrane Science.  

Only 0.01 percent of the Earth's water is fresh water. In contrast, 97 percent of the water on Earth is salt water, making seawater desalination an attractive option for meeting the global demand for fresh water. 

Conventional seawater desalination can generate high-quality fresh water; however, it produces highly concentrated salt water which is usually discharged into the oceans, resulting in serious environmental and ecological problems. Furthermore, the build up of insoluble precipitates fouls the nanofiltration membranes used, making frequent replacement necessary. 

By combining nanofiltration-based fractionation with electrodialysis-driven double displacement (metathesis), a research team from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of Chinese Academy of Sciences have developed a way to fully utilize the highly concentrated waste water.  

Called fracsis (fractionation + electrodialysis), the process uses a commercially-available nanofiltration membrane to first separate ions with different valency. Valency is a measure of the ability to form covalent bonds. Divalent ions such as calcium (Ca²⁺) and magnesium (Mg²⁺) tend to form salts that dissolve poorly and clog up the membrane. To avoid this, the researchers first used a nanofiltration membrane to separate the monovalent and divalent ions in the high salt waste water. 

The separated solutions are then channeled to different electrodes for electrodialysis, where Mg²⁺ migrates to the direction of cathode and SO₄^2- to anode. Both ions then move to adjacent compartments where they form highly stable salts through a process known as double displacement. This prevents the formation of precipitates of MgSO₄, while producing high-purity drinking water at the same time. 

The article can be found at: Zhang et al. (2016) Fracsis: Ion Fractionation and Metathesis by a NF-ED Integrated System to Improve Water Recovery. 

Contact: 

Dr. XIN Hongchuan 

Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences 

Email: xinhc@qibebt.ac.cn