Estimating removals of contaminants of emerging concern from wastewater treatment plants: The critical role of wastewater hydrodynamics

Abstract

Accurate data is needed to evaluate the capacity of wastewater treatments plants (WWTPs) to remove contaminants of emerging concern (CECs). The variability of CEC removals reported in the literature has raised questions about the methods used to estimate removals. In this study, we used the recently proposed "fractionated approach" to account for the influence of hydrodynamics in WWTPs and applied this method for estimating the removal of 23 target CECs. Data on the conductivity and temperature of wastewater at two WWTPs were used to determine the hydraulic model that best described the flow regime of treatment units. Composite samples (24-h) were collected at different stages of treatment over successive days. The concentrations of the target compounds in wastewater were determined by liquid chromatography with mass spectrometry. Different hydraulic models were necessary to define the hydrodynamics at the two WWTPs, resulting in different load fractions to be used in the calculation of removals. For WWTP A, that has a primary clarifier, all target CECs, except triclosan, were poorly removed during this step at efficiencies <30%. On the other hand, the activated sludge treatment unit at both WWTPs removed most target CECs at >70%. This study expanded the application of the fractionated approach to compare the hydraulics of two treatment trains of different configurations, including primary and secondary treatment. It demonstrated the sensitivity of the method to account for variations between the different treatment units. Reliable removals of an extended list of CECs in primary and secondary treatment were also provided in this study.

Keywords: Activated sludge; Fractionated approach; Hydraulic model; Micropollutants; Primary clarification; Removal efficiency.