Comparison of tetracycline rejection in reclaimed water by three kinds of forward osmosis membranes

Comparison of the rejection of trace tetracycline (TC) in the secondary effluent of an anoxic-oxic (AO) system by forward osmosis (FO) was investigated at the mini-lab scale. The effects of different operating conditions including membrane orientation, flow velocity, and draw solution concentration and solute on TC rejection were also explored. The results revealed that TC rejection increased with increasing water flux, but high reverse salt flux may reduce TC rejection through enhanced solution ionic strength. Membranes with a nonwoven structure could reduce TC rejection via increased flow velocity. In the pressure retarded osmosis (PRO) mode, rejection of charged TC was higher than in the FO mode because of enhanced electrostatic repulsion. In addition, the reverse draw solute could hinder the forward diffusion of TC, thus leading to a decline in TC rejection. The cellulose triacetate with embedded polyester screen (CTA-ES) membrane displayed consistently higher TC rejection than that of the cellulose triacetate with a cast nonwoven (CTA-NW) membrane, and the rejection of TC by a thin-film composite with embedded polyester screen (TFC-ES) membrane was relatively lower compared to CTA membranes. These findings provide further insight into TC rejection mechanisms and potentially can be useful for FO process operation in wastewater reclamation.