For treating drinking water and wastewater, ultrafiltration membranes made of Kynar® PVDF offer unrivaled performance in addressing a global challenge.
By 2050, more than 9 billion people will call our planet home and, according to the World Health Organization 60% of them may not have access to clean drinking water. New wastewater treatment plants, improved filtration and seawater desalination processes are of critical importance. Arkema is helping to meet the challenge.
Kynar® PVDF Membranes to micro-filter water
The time-honored tradition of treating wastewater by holding it in a settling pond or tank before filtering it through sand is being supplanted today by more efficient, more compact membrane filtration.
This process forces the water through thousands of tubular modules containing long, porous, semi-permeable hollow fibers of 1 to 2 mm in diameter, that trap suspended solids and impurities. The fibers are usually made of PVDF (polyvinylidene fluoride), a polymer that can withstand the high-pressure water inflow and the chlorine-based chemicals used to clean the membranes. It’s one of the most promising applications of Arkema’s Kynar® PVDF. "With pore diameters from 0.02 to 0.1 microns (20 to 100 nanometers), these Kynar® PVDF fibers can filter the water more finely than sand, filtering bacteria and viruses" says Bernard Schlinquer, Kynar® Business Manager.
The membrane filtration process, adopted by most newer treatment plants, produces water of excellent quality. However, it uses a lot of energy and, unlike conventional sand-based systems, cannot trap certain ultra-fine particles, such as drug residues and certain viruses. The water must therefore be treated chemically after filtration.
Arkema innovates with ultra-filtration and hydrophilic membranes
Tapping into our expertise in synthesizing block copolymers, we have developed a new grade of nanostructured Kynar® DH 100 PVDF for even more efficient membranes. Pore size has been reduced to between 0.01 and 0.1 microns (10 and 100 nanometers) - or 10 times smaller than a typical PVDF membrane - to capture the ultrafine particles: they typically retain more than 99% of bacteria and viruses “but above all, membranes made from Kynar® DH 100 PVDF, stand out for their long-lasting hydrophilic property: they can filter larger water volumes (20 % more) with the same energy consumption, and have double the lifespan of more traditional products” says Bernard Schlinquer.
These Kynar® PVDF membranes are used in portable kits, developed in partnership with the module manufacturer Polymem, for drinking water solutions in developing countries.
More widely, drinking water processing plants, which must meet very high standards in terms of filtration, are the ideal application for Kynar® PVDF fibers. They are used widely in industry too, particularly for treating wastewater. “We work with many membrane bioreactor manufacturers in China, the United States, and Europe,” says Schlinquer. In 2019, thewastewater market represented two-thirds of sales of Kynar® ultrafiltration products.
The Kynar® PVDF filtration boom
At present, hollow-fiber membrane systems account for only 5% of the processes installed in water treatment plants. The remaining 95% still use conventional sand filtration systems. For the last several years, however, most new water treatment plants worldwide rely on the membrane-filtering process and an estimated 75% of these membranes are made of PVDF. The process is growing at 8 to 10% a year. Kynar® PVDF continues to grow compare to other materials more chemically vulnerable to the chlorine-based chemicals used for cleaning. Arkema projects an annual growth of about 25% in Kynar® PVDF sales for water filtration applications.