Chemical cleaning protocols for thin film composite (TFC) polyamide forward osmosis membranes used for municipal wastewater treatment

• Searching for proper chemical cleaning protocols for TFC FO membrane was carried out.
• Alconox detergent was feasible for CTA cleaning but detrimental to TFC FO membranes.
• NaOH cleaning resulted in increased water and salt fluxes and acid cleaning restored them.
• An optimal cleaning scheme was 0.1% NaOH/0.1% SDS mixture followed by acid cleaning.

Recently, thin film composite (TFC) polyamide forward osmosis (FO) membranes have received attention for their potential water- and energy-related applications. TFC FO membranes have been shown to achieve both higher water flux and better solute rejection than cellulose triacetate (CTA) FO membranes. One of the major obstacles in widespread membrane use is the irreversible fouling that occurs during long-term filtration processes such as wastewater treatment. The development of proper chemical cleaning protocols for TFC FO membranes holds the key to achieving sustainable operation of FO processes. In this study, virgin membrane samples were exposed to chemical cleaning agents to determine their effects on membrane properties. In Addition, the water flux recovery efficiency of selected chemical agents was investigated by measuring the change in water flux following chemical cleaning of fouled membrane samples. Exposure of TFC membranes to commercial cleaning detergents (0.8% EDTA and 1% Alconox mixture) resulted in a dramatic increase in water and solute fluxes. Alkaline soaking led to a slight increase in the relative water and solute fluxes, while acid exposure led to a decrease in these fluxes. It was also found that the changes in membrane properties caused by Alconox exposure were irreversible, while the impacts of alkaline exposure were reversible, demonstrating that the Alconox exposure caused damage to TFC membranes. Various cleaning protocols were then developed and tested on wastewater-fouled TFC membranes. Results indicate that the use of 0.1% NaOH/0.1% sodium dodecyl sulfate (SDS) mixture cleaning followed by acid cleaning with either 2% citric acid or 0.5% HCl was the most effective cleaning strategy.