A unique class of chlorine-resistant membranes is set to enhance the performance of processes requiring zero liquid discharge. NALA Membranes (Morrisville, N.C.; www.nalmembranes.com) has developed highly stable and durable membranes based on sulfonated polysulfone materials that overcome many of the limitations of traditional reverse-osmosis (RO) membranes based on polyamide thin-film composite (TFC) materials. “The chemical bonds that make up polysulfones have inherently high dissociation strengths that make them stable against oxidative cleavage. Moreover, unlike the industry-standard polyamide membranes, polysulfones lack carbonyl groups that are prone to both nucleophilic and electrophilic attack, making them more stable over a wide range of pH relative to either polyamides or cellulose acetate membranes. NALA’s sulfonated polysulfones leverage a durable polysulfone backbone that is functionalized with sulfonate ions to enhance hydrophilicity and ionic-rejection characteristics,” says Sue Mecham, CEO of NALA Membranes.
Source: NALA Membranes
This level of chemical stability helps to avoid the risk of biofouling, because facilities can maintain a low concentration of strong oxidants, such as hypochlorite, in the feedwater to prevent biofilm formation. And to prevent damage from organic fouling, high concentrations of strong oxidants can be used for cleaning, something that is not possible using traditional polyamide membranes. According to Mecham, NALA is currently the only company offering sulfonated polysulfone thin-film composite RO membranes with high chlorine resistance and durability.
The company has also devised a novel, low-waste roll-to-roll manufacturing process to produce its membranes. “Unlike conventional polyamide thin-film composite membrane fabrication, NALA’s proprietary process is compatible with a broad range of polymeric materials — unlocking potential for membrane innovation across diverse liquid and gas separations,” notes Mecham. The company’s proprietary manufacturing process imbues the membranes with a smooth surface, which decreases fouling and scaling rates when compared to the rougher surfaces of traditional RO membranes, where particulates are more likely to become trapped.
NALA Membranes is currently constructing a new manufacturing facility in North Carolina, which is set to significantly increase production capacity in 2026. NALA’s membranes have already seen application in a handful of industrial wastewater demonstrations in India, and work is ongoing to achieve NSF 61 certification for drinking water safety. “Early customer demand has been strong, with pilot programs already underway for wastewater treatment in textiles, food-and-beverage and oil-and-gas applications,” says Mecham.