Treatment of algal toxins in drinking water with UV/Cl2 and UV/H2O2 advanced oxidation: toxicity of transformation products and effect on disinfection byproduct formation
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Date
2020-09-16
Authors
Advisors
Journal Title
Series/Report No.
UNC-WRRI;488
WRRI Project;19-01-U
WRRI Project;19-01-U
Journal ISSN
Volume Title
Publisher
NC Water Resources Research Institute
Abstract
This project evaluated treatment alternatives for water resources contaminated with algal toxins. An established advanced oxidation process (UV/H2O2) was compared with an emerging one (UV/Cl2) in terms of (a) effectiveness for detoxifying the three most common variants of algal hepatotoxin microcystin (LR, RR and YR), and (b) potential to increase the formation of regulated disinfection byproducts [four trihalomethanes (THMs) and nine haloacetic acids (HAAs)] and an unregulated nitrogenous byproduct (NDMA) due to the interaction of the process with algal organic matter and nitrate in the water. The toxicity of the products was assessed with a protein phosphatase inhibition assay (PP2A). Products were also analyzed with HPLC/MS/MS. Disinfection byproducts were assessed using the corresponding EPA methods (551.1, 552.3 and 521) with any modifications described in the report. The results shown that both methods are effective against the three microcystins; however, microcystin LR is also highly susceptible to reaction with chlorine and UV/Cl2 offers an additional advantage of direct chlorine reaction. The PP2A assay was not able to conclusively determine whether the transformation products retain any residual hepatotoxicity; however, HPLC/MS/MS analysis indicated that ADDA group of the molecule that is considered to be responsible for microcystin toxicity is a susceptible reaction site in both advanced oxidation and direct chlorination, and the resulting products are likely non-toxin. More work needs to be done to determine it with certainty, which may include conducting PP2A assays in pure water samples to avoid matrix interference with the analysis, or performing ADDA-specific assays (e.g. ELISA). Addition of nitrate or algal DOM to the sample matrix did not significantly affect the formation of THMs and HAAs, with the exception of chloroform. However, the effect on chloroform, while statistically significant, is unlikely to affect the regulatory compliance for utilities. On the other hand, NDMA formation was considerably increased by both nitrate and algal DOM. NDMA remained below 10 ng/L which is set as advisory level in some states in all samples. The amounts of nitrate and algal DOM used in the experiments were on the high end of environmentally relevant range. However, formation of nitrogenous DBPs warrants additional investigation.
