Aaron Dotson Dissertation defense

Wastewater discharge, agricultural runoff, and algal blooms have led to increasing enrichment of dissolved organic nitrogen (DON) in surface water. Drinking water regulations in the United States have focused the industry on the dissolved organic carbon (DOC) component of dissolved organic matter (DOM). Consequently, little is known about DON occurrence and fate during drinking water treatment. This dissertation explores the occurrence, composition, and disinfection by-product (DBP) formation potential of DON and amino acids, a potentially dominant class of group of nitrogen enriched compounds, in surface waters enriched in DON.

A field survey of 16 wastewater and/or algal-influenced raw and treated drinking waters reveals an average DON concentration of 290 micrograms nitrogen per liter and 206 micrograms nitrogen per liter in raw and treated waters, respectively. Total amino acids (TAAs) accounted for, on average, 15 percent of the DON in the raw water and only 4.1 percent, on average, in the treated water, indicating that water treatment processes preferentially remove the amino acid fraction. Flocculation/sedimentation physically removed the largest amount of TAAs, while application of oxidants removed TAAs but was suspected lead to chemical transformation.

DOM from six DON enriched source waters (two wastewater plants, two surface waters, and two laboratory generated samples) were fractionated to reveal nitrogen-enriched biogenic colloids, hydrophobic neutrals, amphiphilics, and hydrophilic bases. Biogenic colloids were composed of cellular debris and accounted a notable portion (20 to 60 percent by mass) of the total DOM. Nitrogen-enriched DOM isolates formed more nitrogenous DBPs than nitrogen depleted isolates. Wastewater DOM produced greater yields of cyanogen chloride than surface water DOM. Highly nitrogen-enriched hydrophilic bases had higher yields of N-nitrosodimethylamine than other isolates.

The nitrogen content of drinking water supplies will continue to increase as a result of human activities. The treatment of this DON-enriched water is likely to result in higher concentrations of toxic nitrogenous DBPs, While DON and N-DBPs are currently unregulated, research, like that done for this dissertation, builds a foundation of knowledge of existing treatment capabilities and DBP management to guide utilities as regulations for nitrogen containing organics are created.