Daniel Logan McCurry
Published: 2016
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Disinfection of potable water is one of the great public health victories of the twentieth century, responsible for the avoidance of millions of deaths due to waterborne illness. However, application of disinfectants, typically chemical oxidants, leads to formation of hundreds of trace contaminants, often carcinogens, and consumption of chlorinated water has been epidemiologically linked to bladder cancer and certain birth defects. Eleven of these compounds are federally regulated in drinking water, but certain non-regulated disinfection byproducts (DBPs) are orders of magnitude more toxic than currently regulated compounds. Two specific DBPs, chloropicrin and N-nitrosodimethylamine (NDMA), are especially genotoxic, and are associated with nitrogen input into drinking water supplies. Wastewater-impacted drinking water and recycled wastewater are enriched in the precursors of these compounds, and their formation during potable water treatment is likely to grow, as wastewater increasingly contributes to the water supply. This thesis focuses on applying the tools of environmental organic chemistry to identify the chemical precursors and formation mechanisms of these compounds, leading to strategies for their control during water treatment. In particular, ozonation of primary and secondary amine compounds, leading to formation of nitro compound intermediates, was found be responsible for chloropicrin formation during water treatment. Secondary N-methylamines and primary amines geminal to facile leaving groups were particularly potent precursors, forming chloropicrin at up to 50% yield when exposed to ozone followed by chlorine. Based on this predominant formation pathway, chloropicrin precursors may be oxidized upstream of ozone addition to prevent chloropicrin formation. Strategies for controlling NDMA formation, a major concern during wastewater recycling, were developed based on an understanding of the chemical composition of NDMA precursors, and chloramines, the primary disinfectant applied during wastewater reuse. Minor modifications to wastewater recycling operations, in particular switching from low-pressure to medium-pressure mercury lamps for ultraviolet light treatment, and minor adjustments in the application of chloramines, were shown to dramatically reduce NDMA concentrations in final effluent. Finally, the effluent from a new, all-anaerobic wastewater treatment system was demonstrated to more efficiently remove trace contaminants and DBP precursors than conventional aerobic treatment, suggesting that this energy-saving technology may also be more suitable for water reuse than conventional treatment. These findings facilitate reducing the chronic health risk associated with consumption of (intentionally or unintentionally) recycled wastewater.
