Multi-functional tannic acid (TA)-Ferric complex coating for forward osmosis membrane with enhanced micropollutant removal and antifouling property

A novel tannic acid - ferric (TA-Fe) complex coating was applied to commercially available cellulose triacetate (CTA) forward osmosis (FO) membrane to enhance membrane performance. Notably, the coated membrane attained a better water/salt selectivity than the control membrane and it had a mild water permeability loss of about 13.6%. Consequently, when the coated membrane is operated in the FO system, the reverse salt flux was smaller as compared to the uncoated commercially available membrane. Also, the rejection of three selected micropollutants improved and this is due to both increased membrane hydrophilicity and the decreased membrane effective pore size. In the membrane fouling tests, with the support layer facing the feed solution (PRO mode), the normalized water flux for the uncoated membrane decreased from 1 to about 0.4. For our membrane with a coating layer on the support layer side, the normalized water flux was higher than 0.5 after the test under the same conditions, confirming its improved antifouling property. The improvement was due to both the coated membrane's decreased surface roughness and the increased interaction energy barrier between the foulant and membrane. These test results represent a new contribution to wastewater treatment using FO based on the success of the authors' novel coating method and its potential to offer multiple performance improvements in osmotic pressure-driven membrane processes.