Membranes with polydopamine coatings

A method of improving membrane rejection properties by depositing a coating on one or more membranes, the method comprising:

• (i) preparing a coating solution comprising one or more active agents, wherein said one or more active agents are polydopamine, hydroquinone, catechol, or a mixture thereof;
• (ii) preparing a coated membrane by circulation of the coating solution through a membrane for a given duration of time while bubbling air or oxygen into the coating solution;
• (iii) after completing step (ii), removing polymer particles formed in the coating solution using a 0.1-5 μm pore size filter to prepare a filtered coating solution;
• (iv) reusing the filtered coating solution from step (iii) for a new set of membranes;
• and
• (v) disposing of residual coating solution by
• (a) storing the coating solution in a tank;
• (b) bubbling oxygen or air through the tank for a period of 12-48 hrs to fully polymerize the one or more active agents;
• (c) removing polymer particles from the coating solution;
• and
• (d) adjusting the pH of the coating solution to neutral pH and adding 50-100 ppm bleach to oxidize any residual active agent;
• wherein the pH of the coating solution is changed from basic to acidic between steps (iii) and (iv) to temporarily stop polymerization and preserve the coating solution.