Thermo‐responsive polymer to clean fouled forward osmosis membrane after wastewater treatment: Excellent flux recovery

Abstract

Thermally responsive polymers (TRPs) have gained significant attention in the past decade due to their unique phase transition behavior, those exhibiting changes in properties with temperature variations. In water, hydrophilic block copolymers form helical structures that can transform into hydrophobic globules above the lower critical solution temperature (LCST). Fouling is one of the limiting issues for the forward osmosis (FO) process in wastewater treatment. In this work, after the treatment of wastewater from the paper and pulp industries, foulants were removed from the surface of the commercial polyamide thin‐film composite membrane of the FO process using polyvinyl methyl ether (PVME), a TRP with an LCST of 35–37°C. PVME was mixed with different aqueous solutions to form cleaning solutions. Foulant cleaning experiments utilized a 1% PVME (w/v) solution in 300 mL of de‐ionized (DI) water, while 1 M NaCl solution served as the draw solution (DS) in the FO process. Comparing the water flux (J) and change in membrane hydraulic resistance (Rf) among pristine, fouled, and cleaned membranes revealed a 56.67% increase in water flux and a 51.68% decrease in membrane resistance after PVME mixed with DI water cleaning solution showcasing its effectiveness in improving membrane performance and reducing fouling. The cleaning efficiency of two solutions, that is, 1% PVME mixed in DI water and 1% PVME mixed in 1 M aqueous urea solution, is compared. Results showed that the former cleaning solution helped to obtain 32.62% higher water flux and 56.05% less membrane resistance. Various membrane characterizations are performed, such as field emission scanning electron microscopy (FE‐SEM), which characterizes the membrane's pore structure and surface morphology, while a contact angle analyzer assesses hydrophilicity. This research highlights the use of TRPs as effective cleaning agents, enhancing membrane performance by effectively removing foulants on the membrane surface. Investigating alternative cleaning solutions also provides insights for optimizing water treatment processes.Highlights Cleaning of fouled thin‐film composite membrane using thermal‐responsive polymers (TRPs). Polyvinyl methyl ether, a TRP with an lower critical solution temperature of 35–37°C used as a cleaning agent. 60% increase in water flux was observed after the single‐step cleaning process. Multiple uses of TRP for cleaning performed with no membrane damage.