Desalination history continues to be made at the University of California-Los Angeles’ (UCLA) Henry Samueli School of Engineering where researchers have announced the development of a new RO membrane that is said to improve erformance and lower operating costs. The new development took place at the same school at which Sidney Loeb and Srinivasa Sourirajan produced the first functional synthetic RO membrane from cellulose acetate in 1959.
The new thin film nanocomposite (TFN) membranes are fabricated using a unique process for synthesizing super-hydrophilic nanoparticles and integrating them into a polyamide thin film matrix on a polysulfone UF support. The process, developed by a team led by civil and environmental engineering assistant professor Eric Hoek, requires virtually no change in existing membrane manufacturing methods, and the engineered nanoparticles provide increased water permeability and better rejection of salts, organics and other contaminants.
Dr Hoek told WDR, “In principal, there is nothing different from the way our membrane removes solids from water. However, we can tailor the membrane properties to dramatically improve energy efficiency without compromising its stability, and at the same time, modify it to possess intrinsically biocidal properties.”
Other types of commercially-available nanoparticles exist, but the nanomaterials designed at UCLA have been specifically designed for this desalination application. Rather than just modifying its surface, the membrane itself is changed. The engineered nanoparticles are uniformly dispersed within the membrane matrix, and can be structured to create molecular tunnels to dramatically vary performance. Not only can water’s permeability be increased by 75 percent, the new membrane has improved rejection characteristics.
To visualize how the TFN membrane’s molecular tunnels improve performance, imagine a thin polyamide film with relatively hydrophobic pores periodically interrupted by nanoparticles having super-hydrophilic pores. While water diffuses through the polyamide pores only under high applied pressure, water penetrates through the nanoparticle pores with very little applied pressure. Because the nanoparticle pore walls are even more negatively charged than the membrane surface, ion exclusion is enhanced in concert with increased water permeability. The super-hydrophilic nanoparticles also enhance fouling resistance by making the overall membrane more hydrophilic.
The improvements will translate into lower costs. “We estimate the cost of the TFN membrane could be one to ten percent higher than the cost of an existing element, but the improved performance could result in an overall decrease in the capital cost of a system and a total energy cost reduction of 25 percent,” said Hoek.
Researchers will take their design from bench to pilot scale and conduct field studies in 2007. The University has a partnership with NanoH₂O LLC to commercialize the technology and new membranes could be commer-cially available within one or two years.