Drinking water treatment using UV and UV/hydrogen peroxide: An analysis of photochemical properties and efficacy of treatment for removal of microcontaminants

Pharmaceuticals and personal care (PPCPs) and endocrine disrupting compounds (EDCs) are microcontaminants that are widely distributed in the aquatic environment and have been found in both untreated and treated drinking water. In this study, transformation rates for 15 model PPCPs and EDCs were monitored in deionized water (DIW), dechlorinated tap water (PTW) from Peterborough, Ontario (Le. high DOM, hard water), and water from Plastic Lake (PLW) in Haliburton County, Ontario (Le. low DOM, soft water) under treatment with low-pressure and medium-pressure mercury arc lamps. In some treatments, waters were amended with 4 mg/L H2O2 and/or 15 mg/L NO3 -. Spectrophotometric titrations were performed to determine micropolluant pKas. Time-based photochemical rate constants, molar absorption coefficients, and quantum yields (mol/einstein) were determined for irradiations at 253.7 nm in DIW at pH 7.2 for sulphamethoxazole, sulphachloropyridazine, nonylphenol, acetaminophen, and triclosan. The rate constants for loss under direct photolysis with a LP lamp at sub mug/L concentrations were (3.9 +/- 0.7) x 10-4 s-1 for triclosan, (3.8 +/- 0.4) x 10-4 s-1 for sulphamethoxazole, (7.0 +/- 2.4) x 10-5 s-1 for nonylphenol, (5.3 +/- 1.1) x 10-5 s-1 for sulphachloropyridazine, and (2.4 +/- 1.2) x 10-5 s-1 for acetaminophen. Second-order OH· radical rate constants determined using a competition kinetics method with para-chlorobenzoic acid only varied by a factor of two, from 5.2 +/-0.4 x 109 M-1 s-1 for caffeine to 10.8 +/- 0.9 x 109 M-1 s-1 for estrone, which are close to diffusion rates. Without addition of NO3- or H2O2, transformation rates were generally higher in DIW than in PTW. Addition of NO3- increased the rates of transformation for 12 compounds in the three test waters, while rates for bisphenol A, atenolol, and ibuprofen were not influenced. Addition of H2O2 increased removals of all compounds in both DIW and PLW. With the exception of 4-nonylphenol, all compounds showed lower transformation rates in the presence of both added NO3- and H2O2 than with only the larger contributor of the two, indicating that the presence of N03- can compete for reaction with H2O2 and the presence of H2O2 can compete for reactions with N03-. Treatment with UV alone allows for maximum 15 % transformation of microcontaminants at the fluences normally used for disinfection of drinking water. However, the UV/H2O2 treatment method is effective for the removal of microcontaminants from water.;Keywords: UV and UV/H2O2, drinking water treatment, quantum yield, pKa determinations, ·OH radical rate constants, pharmaceuticals and personal care products, Endocrine-disrupting compounds, low-pressure and medium-pressure Hg lamps.