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Ammonia-Mediated Bromate Inhibition during Ozonation Promotes the Toxicity Due to Organic Byproduct Transformation
journal contribution
posted on 2020-07-09, 19:46 authored by Qian-Yuan Wu, Lu-Lin Yang, Xin-Yang Zhang, Wen-Long Wang, Yao Lu, Ye Du, Yun Lu, Hong-Ying HuAmmonia
(NH4+) and hydrogen peroxide (H2O2) have been widely used to inhibit bromate formation
during ozonation. However, organic byproducts can also pose a risk
under these conditions. During bromate inhibition, the influence of
NH4+ and H2O2 on organic
byproducts and their toxicity should be elucidated. Our study found
that NH4+ suppressed organic bromine, but might
result in increased toxicity. Adding 0.5 mg/L of NH4+–N substantially increased both the formation of cytotoxicity
and genotoxicity (DNA double-strand breaks) of organic byproducts
from 0.6 to 1.6 mg-phenol/L, and from 0.3 to 0.8 μg-4-NQO/L
(0.5 mg/L Br–, 5 mg/L O3). NH4+ decreased bromate, but increased the overall toxicity
of the integrated byproducts (organic byproducts and bromate). Organic
nitrogen measurements and 15N isotope analysis showed enhanced
incorporation of nitrogen into organic matter when NH4+ and Br– coexisted during ozonation. NH4+ decreased the formation of brominated acetonitriles,
but enhanced the formation of brominated nitromethanes and brominated
acetamides. These brominated nitrogenous byproducts were partially
responsible for this increase in toxicity. Different from ammonia,
H2O2 could reduce both bromate and the toxicity
of organic byproducts. In the presence of 0.5 mg/L Br– and 10 mg/L O3, adding H2O2 (0.5
mM) substantially suppressed bromate, cytotoxicity formation and genotoxicity
formation by 88%, 63% and 67%. This study highlights that focusing
on bromate control with NH4+ addition might
result in higher toxicity. Efforts are needed to effectively control
the toxicities of bromate and organic byproducts simultaneously.