Date of Award
Doctor of Philosophy (PhD)
Environmental Engineering and Science
David L Freedman
David A Ladner
N-Nitrosamines are a group of probable human carcinogens associated with 10-6 lifetime cancer risks at low ng/L levels in drinking water. N-nitrosamines can form via the reactions between chloramines (i.e., monochloramine, dichloramine) and organic precursors (e.g., secondary, tertiary and quaternary amines). Municipal wastewater effluents are considered one of the major sources of N-nitrosamine precursors that can impact downstream drinking water qualities. Although many studies have investigated the formation of N-nitrosamines in the influents and effluents of wastewater treatment plants (WWTPs), the major sources of N-nitrosamine precursors are still largely unknown. The first objective of this research was to evaluate the occurrences of N-nitrosamine precursors in different sewage components (i.e., blackwaters and greywaters). Results showed that urine blackwater (i.e., raw human urine diluted in tap water 250 times) showed exceptionally high NDMA formation potential (FP, >10000 ng/L). The FP of the other N-nitrosamines tested were more than one magnitude lower than NDMA FP. Urine blackwater was the predominant contributor to NDMA (i.e., >90%) and N-nitrosopyrrolidine (NPYR) FP (i.e., 65%) in domestic sewage, while laundry greywater was the major source of most other N-nitrosamine FP (i.e., 55%-100%). In contrast, N-nitrosamine formation under the uniform formation condition (UFC) from all sewage components was generally <100 ng/L, far lower than N-nitrosamine FP.
Because of the huge discrepancies between N-nitrosamine UFC and FP, the potential effects of different factors (i.e., pH, dissolved organic carbon (DOC), specific ultraviolet absorbance at 254 nm (SUVA254), Br-) on NDMA UFC and FP were examined. Under different pH conditions (i.e., pH 6.0, 6.8, 7.8 and 8.8), all model NDMA precursors tested achieved peak NDMA UFC at pH 6.8-7.8 in DDW, regardless of compounds’ pKa values (i.e., 3.8-13.6). The peak NDMA FP tended to be achieved at a relatively higher pH than NDMA UFC. In surface waters with higher DOC or SUVA254, NDMA UFC tended to be lower, while NDMA FP tended to increase with increasing DOC. The effects of Br- (i.e., 1000 µg/L) on NDMA UFC depended on pH. Linear regression analysis indicated that NDMA UFC poorly correlated (R2 = 0.04-0.06, n = 17) with NDMA FP in different surface waters.
The removal of NDMA FP and removal of NDMA UFC from model NDMA precursors were then evaluated during batch activated sludge (AS) treatment tests. Among the four model compounds tested, trimethylamine (TMA) and minocycline (MNCL) were readily removed (i.e., 77%-100% removals of NDMA FP) during 24-h AS treatment, ranitidine (RNTD) was moderately removed (i.e., 34%-87% removals of NDMA FP), and sumatriptan (SMTR) was the least removable (i.e., 29%-46% removals of NDMA FP). Increasing incubation time (or hydraulic retention time (HRT)) and solids retention time (SRT) favored the removal of NDMA FP from RNTD. Biosorption was found to be the major deactivation pathway of the amine-based pharmaceuticals (i.e., RNTD, MNCL and SMTR) tested, while biodegradation was the major deactivation pathway of TMA. Adding different biostimulants (e.g., glucose, acetate, benzoate and ammonia) insignificantly affected the removal of NDMA FP from RNTD. Non-specific oxygenase (i.e., phenol 2-monooxygenase) may play an insignificant role affecting the removal of NDMA FP from RNTD, especially at extended incubation time (i.e., 5-20 d). Removal of NDMA UFC from the tested compounds was generally comparable to the removal of their NDMA FP, except for MNCL which yielded negligible NDMA UFC before and after AS treatment.
Finally, removal of N-nitrosamine precursors from sewage components (i.e., blackwaters and greywaters) and WWTP influents during the AS treatment was investigated under both FP and UFC tests. Removal of N-nitrosamine FP from sewage components depended on precursor sources (i.e., blackwaters and greywaters) and N-nitrosamine species. Increasing incubation time from 6 to 24 h enhanced the removal of N-nitrosamine FP. Removal of N-nitrosamine FP from WWTP influents mainly depended on AS sources during the batch treatment tests, rather than the types of wastewater influents. Among the three AS (i.e., domestic rural, domestic urban and textile AS) tested, the rural domestic AS showed relatively higher removal of N-nitrosamine FP from biologically originated precursor sources (e.g., urine blackwater, shower greywater not containing any personal care products, and kitchen greywater containing food leachates only). On the other hand, the textile AS exhibited higher removal of N-nitrosamine FP from sewage components containing detergents or personal care products (e.g., shower greywater containing shampoo, kitchen greywater containing dishwashing detergent, and laundry greywater containing laundry detergent). Different from N-nitrosamine FP, N-nitrosamine UFC from most sewage components increased after 6 or 24-h AS treatment.
Zhang, Xiaolu, "Impact of Biological Wastewater Treatment on the Reactivity of N-Nitrosodimethylamine (NDMA) Precursors" (2020). All Dissertations. 2664.