Effects of powdered activated carbon dosing on sludge characteristics and estrogen removal in membrane bioreactors

Sludge characteristics associated with filterability as well as the removal of a natural estrogen 17beta-estradiol (E2) and a synthetic estrogen 17alpha-ethyinylestradiol (EE2) were investigated in submerged membrane bioreactors (MBR) with and without the addition of powdered activated carbon (PAC) under the same experimental conditions. Positive impacts of PAC dosing on membrane fouling and the removal of E2 and EE2 were demonstrated over a six months stable operational period. Experimental results showed that PAC dosing resulted in lower concentrations of soluble extracellular polymeric substances (EPS) and colloidal total organic carbon (TOC) in the PAC-MBR sludge. The average soluble EPS and colloidal TOC concentrations in the PAC-MBR sludge was 60.1% and 61.8% lower than the control MBR sludge, respectively. Regardless of PAC dosing, concentrations of colloidal TOC were strongly related to concentrations of soluble EPS and soluble carbohydrates in the sludge. In addition, the mean flocs size of the sludge with PAC dosing was shifted from 49.4 microm to 60.3 microm. PAC dosing in the MBR increased the removal rates of E2 and EE2 by 3.4% and 15.8%, respectively.