Efficiency of conventional drinking-water-treatment processes in removal of pharmaceuticals and other organic compounds

Abstract

Samples of water and sediment from a conventional drinking-water-treatment (DWT) plant were analyzed for 113 organic compounds (OCs) that included pharmaceuticals, detergent degradates, flame retardants and plasticizers, polycyclic aromatic hydrocarbons (PAHs), fragrances and flavorants, pesticides and an insect repellent, and plant and animal steroids. 45 of these compounds were detected in samples of source water and 34 were detected in samples of settled sludge and (or) filter-backwash sediments. The average percent removal of these compounds was calculated from their average concentration in time-composited water samples collected after clarification, disinfection (chlorination), and granular-activated-carbon (GAC) filtration. In general, GAC filtration accounted for 53% of the removal of these compounds from the aqueous phase; disinfection accounted for 32%, and clarification accounted for 15%. The effectiveness of these treatments varied widely within and among classes of compounds; some hydrophobic compounds were strongly oxidized by free chlorine, and some hydrophilic compounds were partly removed through adsorption processes. The detection of 21 of the compounds in 1 or more samples of finished water, and of 3 to 13 compounds in every finished-water sample, indicates substantial but incomplete degradation or removal of OCs through the conventional DWT process used at this plant.

Introduction

More than 100,000 synthetic chemicals are used in a variety of domestic, industrial, and agricultural applications (Jørgensen, 2004). Numerous studies have documented that many of these compounds, including pharmaceuticals, fragrances and flavorants, flame retardants and plasticizers, detergent metabolites, components of personal care products, and products of petroleum use and combustion are incompletely degraded or removed during wastewater treatment and are persistent in the aquatic environment. Reviews of the occurrence and fate of organic compounds (OCs) in wastewaters and the aquatic environment are available (Metcalfe et al., 2004, Focazio et al., 2004, Daughton, 2001, Halling-Sørensen et al., 1998, Daughton and Ternes, 1999). Fewer studies have documented the occurrence of these OCs in drinking-water supplies. Exceptions include documentation of low-level concentrations of OCs in plant-scale studies of drinking-water supplies (Loraine and Pettigrove, 2006, Petrovic et al., 2003, Adams et al., 2002, Ternes et al., 2002, Reddersen et al., 2002, Heberer and Stan, 1997) and evaluation of their fate in laboratory-scale simulations of drinking-water-treatment (DWT) processes (Westerhoff et al., 2005, Huber et al., 2005, Pinkston and Sedlak, 2004, Zwiener and Frimmel, 2000).

In 2001, the potential for 106 OCs to survive a conventional DWT process and persist in finished, potable water was investigated (Stackelberg et al., 2004). The results provided the first documentation that a wide variety of OCs, most of which are currently unregulated in drinking-water supplies, can survive conventional DWT, but limitations in the study design precluded quantitative comparison of the degradation or removal of OCs by individual water treatments. Subsequent sampling at the same DWT plant in 2003 by the U.S. Geological Survey in cooperation with the New Jersey Department of Environmental Protection addressed these limitations by including (1) collection of multiple time-composited water samples at each treatment step to account for retention time through the DWT plant and diurnal variations in source-water quality, and (2) collection of solids samples for evaluation of the effectiveness of adsorptive processes in removing OCs. This paper uses data from the 2003 sampling to evaluate the average percent removal (concentration decreases) and fate of OCs that were detected in the DWT plant's source waters.