Simultaneous powdered activated carbon dosage for micropollutant removal on a municipal wastewater treatment plant compared to the efficiency of a post treatment stage

Abstract

The application of powdered activated carbon (PAC) for the removal of organic micropollutants (OMP) at two different points of a municipal wastewater treatment plant (WWTP) was investigated. In one activated sludge tank (AST) PAC was dosed into the nitrification zone. Compared to that a post treatment stage was operated where PAC was dosed after the secondary clarifier of the AS process. Experiments included different PAC dosages between 5 and 20 mg/L and the removal rates for thirteen wastewater relevant OMP were evaluated. By dosing PAC simultaneously into the nitrification zone bisphenol A (BPA), benzotriazoles (BTRs), metformin (METF) and metoprolol (METO) were reduced by over 80% at the dose of 20 mg/L. Removal rates above 60% were found for diclofenac (DCF) (63%), carbamazepine (CMZ) (79%), isoproturone (ISO) (77%) and sulfamethoxazole (SMX) (75%) whereas artificial sweeteners were poorly reduced. Approximately half of the PAC dose was needed to achieve equal removal rates in the post treatment stage. To estimate OMP removal rates in dependence to the PAC dosage the normalized PAC dosage (PAC/DOC) was calculated. For simultaneous PAC dosage the PAC/DOC ratio for estimating OMP removal was applicable for substances which are very good adsorbable.