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Download fileTAML/H2O2 Oxidative Degradation of Metaldehyde: Pursuing Better Water Treatment for the Most Persistent Pollutants
journal contribution
posted on 18.04.2016, 00:00 authored by Liang
L. Tang, Matthew A. DeNardo, Chakicherla Gayathri, Roberto R. Gil, Rakesh Kanda, Terrence J. CollinsThe extremely persistent
molluscicide, metaldehyde, widely used
on farms and gardens, is often detected in drinking water sources
of various countries at concentrations of regulatory concern. Metaldehyde
contamination restricts treatment options. Conventional technologies
for remediating dilute organics in drinking water, activated carbon,
and ozone, are insufficiently effective against metaldehyde. Some
treatment plants have resorted to effective, but more costly UV/H2O2. Here we have examined if TAML/H2O2 can decompose metaldehyde under laboratory conditions
to guide development of a better real world option. TAML/H2O2 slowly degrades metaldehyde to acetaldehyde and acetic
acid. Nuclear magnetic resonance spectroscopy (1H NMR)
was used to monitor the degradationthe technique requires
a high metaldehyde concentration (60 ppm). Within the pH range of
6.5–9, the reaction rate is greatest at pH 7. Under optimum
conditions, one aliquot of TAML 1a (400 nM) catalyzed
5% degradation over 10 h with a turnover number of 40. Five sequential
TAML aliquots (2 μM overall) effected a 31% removal over 60
h. TAML/H2O2 degraded metaldehyde steadily over
many hours, highlighting an important long-service property. The observation
of metaldehyde decomposition under mild conditions provides a further
indication that TAML catalysis holds promise for advancing water treatment.
These results have turned our attention to more aggressive TAML activators
in development, which we expect will advance the observed technical
performance.
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TAML activators60 hpH rangeguide developmentacetic aciddrinking water sourceswater treatmentdegrades metaldehydemetaldehyde decomposition1 H NMRConventional technologiesTAML catalysisdrinking waterUVBetter Water Treatment10 htreatment optionslaboratory conditionsresonance spectroscopyTAML 1reaction rateworld optionPersistent PollutantsMetaldehyde contaminationturnover numberpH 7.treatment plants