Tannic acid as a natural organic matter surrogate in ultrafiltration membrane process

Natural organic matter (NOM) is a mixture of organic compounds that derived from decayed plant and animals through microbial activity. Since NOM can react with chlorine disinfectants and form carcinogenic disinfection byproducts (such as trihalomethanes and haloacetic acids), its removal prior to disinfection is essential to ensure safe drinking water production. Ultrafiltration (UF) membranes, which have emerged as an effective method for NOM removal, offer advantages over conventional treatments, such as reduced chemical usage, smaller waste volumes, and great NOM removal efficiency. Tannic acid (TA), a naturally occurring organic compound, has been less studied in membrane filtration compared to humic acid (HA), which has been widely studied as a representative of NOM. Compared with HA, TA has a lower molecular weight and higher water solubility. In this study, we evaluated TA as a NOM surrogate in UF membrane filtration. The removal efficiency of TA was 80.8 ± 1.17 %, which was higher than removal efficiency of 44.4 ± 5.30 % for HA. The presence of TA led to low initial normalized water flux of 24.9 ± 4.76 %. The effects of water chemistry − including the initial TA concentration, pH, and background ions (Na⁺, Ca²⁺, Mg²⁺, and SO₄^2-) at different ionic strengths − on TA removal were analyzed. Additionally, membrane adsorption experiments and zeta potential measurements were conducted to elucidate the mechanisms governing the interactions of TA molecules with the UF membranes.