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.