Assessing the population equivalent and performance of wastewater treatment through the ratios of pharmaceuticals and personal care products present in a river basin: Application to the River Thames basin, UK.

The quality of surface waters in lowland rivers is largely dependent on the efficiency of wastewater treatment. Even in the developed countries, there have been difficulties in evaluating the effectiveness of wastewater management and the proportion of wastewater content (WWC) in the river, as well as in estimating the contributing human population. This study aimed to develop a wastewater quality and quantity assessment based on the occurrence of pharmaceuticals in the receiving waters. A survey of 53 pharmaceuticals in 324 samples (river water and influent and effluent of sewage (wastewater) treatment plants) was carried out in southern England in the River Thames catchment over four years. Carbamazepine was selected as stable marker and from its concentration WWC in the rivers and cumulative human populations along the catchment were estimated. The estimated population had a strong relationship (R2=0.94) with that reported by the local water company. The concentration ratio of the labile marker caffeine to carbamazepine indicated the efficiency of wastewater treatment in the different treatment systems (i.e. trickling filter or activated sludge) and in the receiving waters. The ratio in some river samples revealed unexpected discharges of untreated or poorly treated wastewater, with a total concentration of the analytes (up to 20μg/L) five times higher than that in treated wastewater. Such information could be valuable to estimate the discharge or occurrence of not only non-targeted chemicals, but also pathogens within the basin.