4 research outputs found
Changes in the components and biotoxicity of dissolved organic matter in a municipal wastewater reclamation reverse osmosis system
<p>The characteristics of dissolved organic matter (DOM) and the biotoxicity of these components were investigated in a municipal wastewater reclamation reverse osmosis (mWRRO) system with a microfiltration (MF) pretreatment unit. The MF pretreatment step had little effect on the levels of dissolved organic carbon (DOC) in the secondary effluent, but the addition of chlorine before MF promoted the formation of organics with anti-estrogenic activity. The distribution of excitation emission matrix (EEM) fluorescence constituents exhibited obvious discrepancies between the secondary effluent and the reverse osmosis (RO) concentrate. Using size exclusion chromatography, DOM with low molecular weights of approximately 1.2 and 0.98 kDa was newly formed during the mWRRO. The normalized genotoxicity and anti-estrogenic activity of the RO concentrate were 32.1 ± 10.2 μg4-NQO/mgDOC and 0.36 ± 0.08 mgTAM/mgDOC, respectively, and these values were clearly higher than those of the secondary effluent and MF permeate. The florescence volume of Regions I and II in the EEM spectrum could be suggested as a surrogate for assessing the genotoxicity and anti-estrogenic activity of the RO concentrate.</p
Dichloroacetonitrile and Dichloroacetamide Can Form Independently during Chlorination and Chloramination of Drinking Waters, Model Organic Matters, and Wastewater Effluents
The increasing usage of organic nitrogen-rich wastewater-
or algal-impacted
waters, and chloramines for secondary disinfection, raises concerns
regarding the formation of haloacetonitriles, haloacetamides and other
nitrogenous disinfection byproducts (N-DBPs). Previous research obtained
contradictory results regarding the relative importance of chlorination
or chloramination for promoting these byproducts, but applied chlorine
and chloramines at different doses and exposure periods. Additionally,
mechanistic work, mostly using model precursors, suggested that haloacetonitrile
and haloacetamide formation should be correlated because hydrolysis
of haloacetonitriles forms haloacetamides. In this work, the formation
of dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) were
compared across a range of chlorine and chloramine exposures for drinking
waters, wastewater effluents, algal extracellular polymeric substances
(EPS), NOM isolates and model precursors. While chlorination favored
formation of DCAN over DCAcAm, chloramination nearly always formed
more DCAcAm than DCAN, suggesting the existence of haloacetamide formation
pathways that are independent of the hydrolysis of haloacetonitriles.
Experiments with asparagine as a model precursor also suggested DCAcAm
formation without a DCAN intermediate. Application of <sup>15</sup>N-labeled monochloramine indicated initial rapid formation of both
DCAN and DCAcAm by pathways where the nitrogen originated from organic
nitrogen precursors. However, slower formation occurred by pathways
involving chloramine incorporation into organic precursors. While
wastewater effluents and algal EPS tended to be more potent precursors
for DCAN during chlorination, humic materials were more potent precursors
for DCAcAm during chlorination and for both DCAN and DCAcAm during
chloramination. These results suggest that, rather than considering
haloacetamides as haloacetonitrile hydrolysis products, they should
be treated as a separate N-DBP class associated with chloramination.
While use of impaired waters may promote DCAN formation during chlorination,
use of chloramines may promote haloacetamide formation for a wider
array of waters
Electron Redistribution in Iridium–Iron Dual-Metal-Atom Active Sites Enables Synergistic Enhancement for H<sub>2</sub>O<sub>2</sub> Decomposition
Developing
efficient heterogeneous H2O2 decomposition
catalysts under neutral conditions is of great importance in many
fields such as clinical therapy, sewage treatment, and semiconductor
manufacturing but still suffers from low intrinsic activity and ambiguous
mechanism understanding. Herein, we constructed activated carbon supported
with an Ir–Fe dual-metal-atom active sites catalyst (IrFe-AC)
by using a facile method based on a pulsed laser. The electron redistribution
in Ir–Fe dual-metal-atom active sites leads to the formation
of double reductive metal active sites, which can strengthen the metal–H2O2 interaction and boost the H2O2 decomposition performance of Ir–Fe dual-metal-atom
active sites. Ir–Fe dual-metal-atom active sites show a high
second-order reaction rate constant of 3.53 × 106 M–1·min–1, which is ∼106 times higher than that of Fe3O4. IrFe-AC
is effective in removing excess intracellular reactive oxygen species,
protecting DNA, and reducing inflammation under oxidative stress,
indicating its therapeutic potential against oxidative stress-related
diseases. This study could advance the mechanism understanding of
H2O2 decomposition by heterogeneous catalysts
and provide guidance for the rational design of high-performance catalysts
for H2O2 decomposition
Toxic Impact of Bromide and Iodide on Drinking Water Disinfected with Chlorine or Chloramines
Disinfectants inactivate
pathogens in source water; however, they
also react with organic matter and bromide/iodide to form disinfection
byproducts (DBPs). Although only a few DBP classes have been systematically
analyzed for toxicity, iodinated and brominated DBPs tend to be the
most toxic. The objectives of this research were (1) to determine
if monochloramine (NH<sub>2</sub>Cl) disinfection generated drinking
water with less toxicity than water disinfected with free chlorine
(HOCl) and (2) to determine the impact of added bromide and iodide
in conjunction with HOCl or NH<sub>2</sub>Cl disinfection on mammalian
cell cytotoxicity and genomic DNA damage induction. Water disinfected
with chlorine was less cytotoxic but more genotoxic than water disinfected
with chloramine. For both disinfectants, the addition of Br<sup>–</sup> and I<sup>–</sup> increased cytotoxicity and genotoxicity
with a greater response observed with NH<sub>2</sub>Cl disinfection.
Both cytotoxicity and genotoxicity were highly correlated with TOBr
and TOI. However, toxicity was weakly and inversely correlated with
TOCl. Thus, the forcing agents for cytotoxicity and genotoxicity were
the generation of brominated and iodinated DBPs rather than the formation
of chlorinated DBPs. Disinfection practices need careful consideration
especially when using source waters containing elevated bromide and
iodide