M3 PM Wastewater Treatment: Analysis, Fate and Removal of Emerging Contaminants
Monday, 14 November 2005: 1:50 PM - 5:30 PM in Ballroom 3

(BED-1117-829403) Transformations of Pharmaceutical Compounds by Chlorination and Dechlorination Processes Used in Wastewater Treatment.

Bedner, M¹, MacCrehan, W¹, ¹ National Institute of Standards and Technology, Gaithersburg, MD, USA

ABSTRACT- Pharmaceutical compounds are increasingly being recognized as an environmental threat. Many are detectable in wastewater treatment plant (WWTP) processes owing to their continuous release through both treated and untreated waste. Reactive pharmaceutical compounds can be expected to be transformed by chlorination, the most widely-used technology for disinfecting wastewater in the US. We have demonstrated that the four pharmaceutical compounds sulfamethoxazole, diclofenac, metoprolol, and acetaminophen react readily with hypochlorite. Acetaminophen, for example, reacts with hypochlorite to form a variety of oxidized, dimerized, and/or ring-chlorinated products, including the two toxicants p-benzoquinone and N-acetyl-p-benzoquinone imine. However, many WWTPs that do not employ or have ineffective nitrification will have significant ammonia concentrations in their wastewater. In those processes, monochloramine, which is a weaker oxidant than hypochlorite, will be the principal disinfectant (unless breakpoint chlorination is employed). Monochloramine transforms acetaminophen, but the reaction is significantly slower and the distribution of products is different than for the reaction with hypochlorite. Dechlorination is another process used by many WWTPs to eliminate chlorine residuals entering the environment via chemical reduction with sulfite. Sulfite may therefore react with the products of the chlorination reactions. In the case of acetaminophen, several oxidized products are readily reduced by sulfite, but the ring-chlorinated products are resistant to dechlorination. Reactions of pharmaceutical compounds with chlorine, monochloramine, and sulfite are being monitored using liquid chromatographic separations and multiple detection modes including ultraviolet absorbance, reductive electrochemistry, and mass spectrometry (MS). MS detection has been used with both electrospray ionization and atmospheric pressure chemical ionization. The role of each of these detectors in product identification will be discussed.

Key words: wastewater, chlorination, pharmaceutical, dechlorination