Enhancement of removal of trace organic contaminants by powdered activated carbon dosing into membrane bioreactors

•PAC addition into MBR initially resulted in high removal of all 22 trace organics.•PAC saturation led to gradual drop in removal of 7 hydrophilic and resistant organics.•Notable among these 7 hydrophilic and resistant organics are fenoprop and diclofenac.•Frequent but smaller dose addition is recommended for efficient PAC use.

This study compared the removal efficiency of 22 widespread trace organic contaminants by a laboratory-scale membrane bioreactor (MBR) with and without direct addition of powdered activated carbon (PAC) into the activated sludge reactor over a period of 312 days. The removal of hydrophilic and biologically persistent trace organic contaminants was immediately improved to above 95% after the addition of PAC into MBR. However, a compound-specific gradual decrease in removal underscored the requirement for the addition of fresh PAC. Adsorption onto PAC-added sludge appeared to play a significant role in the relatively more effective aqueous phase removal of a few resistant compounds such as carbamazepine in this study. A slower reduction in removal efficiency of compounds showing extraordinary persistence such as fenoprop and diclofenac was observed after raising the PAC concentration in the MBR from 0.1 to 0.5 g/L. Nevertheless, comparison of extent of removal in terms of PAC usage indicated the suitability of more frequent dosing of smaller amounts of PAC.