Engineers clean up water pollution with sunlight
Date:
August 11, 2021
Source:
Michigan Technological University
Summary:
In addition to providing vitamin D, helping flowers grow and
creating the perfect excuse to head to the beach, sunlight also
helps break down chemicals in streams, lakes and rivers. Researchers
have developed a comprehensive reactive activity model that shows
how singlet oxygen's reaction mechanisms perform against a diverse
group of contaminants and computes their half-life in a natural
aquatic environment.
FULL STORY ==========================================================================
In addition to providing vitamin D, helping flowers grow and creating
the perfect excuse to head to the beach, sunlight also helps break
down chemicals in streams, lakes and rivers. Researchers from Michigan Technological University have developed a singlet oxygen model to
calculate how particular chemicals break down in surface water.
========================================================================== While swimming pools use blue tiles to mimic the color of the Caribbean,
most surface water is yellow or brown. For example, Tahquamenon Falls,
a popular Upper Peninsula destination, is known for the caramel color of
its chutes. That color comes from leaf and bark debris that make tannins
-- polyphenols, or naturally occurring organic compounds in plants. It's
this debris that absorbs sunlight and creates the singlet oxygen that
degrades contaminants.
Singlet Oxygen This reactive species of oxygen causes what's called photochemical transformation, a process in which light and oxidizing
materials produce chemical reactions. But how long does it take for
a particular chemical to break down under this sunny and vegetative
onslaught? Understanding how many hours or days it takes a particular contaminant to break down halfway helps environmental engineers and
scientists protect our waterways. Knowing a particular chemical's
half-life helps resource managers estimate whether or not that chemical
is building up in the environment.
Daisuke Minakata, associate professor of civil, environmental and
geospatial engineering at Michigan Tech, developed a comprehensive
reactive activity model that shows how singlet oxygen's reaction
mechanisms perform against a diverse group of contaminants and computes
their half-life in a natural aquatic environment.
==========================================================================
"We tested 100 different organic, structurally diverse compounds,"
Minakata said. "If we know the reactivity between singlet oxygen
and contaminants, we can say how long it will take to degrade one
specific structure of a contaminant down to half the concentration."
Minakata's collaborators are graduate students Benjamin Barrios, Benjamin Mohrhardt and Paul Doskey, professor in the College of Forest Resources
and Environmental Science. Their research was published this summer in
the journal Environmental Science and Technology.
Sunshine Oxidizes and Degrades Toxic Chemicals The rate of indirect-sunlight-initiated chemical oxidation is unique to the body of
water; each lake, river or stream has its own distinct mix of organic
matter. And because the process does not occur in the dark, the amount
of sunlight a water body receives also affects reactions. For example,
singlet oxygen plays a partial role in degrading the toxins in harmful
algal blooms and in breaking down the excess nitrogen and phosphorus
produced by agricultural runoff.
The reactive oxygen species also has benefits beyond our favorite lakes
and rivers.
"Singlet oxygen can be used for disinfection of pathogens," Minakata
said. "It can oxidize chemicals in drinking water or wastewater
treatments. There are many ways to use this strong chemical oxidant for
many purposes in our lives." Moving Beyond Reactions Toward Byproducts
With the half-life calculations established by Minakata's model, the
research team plans to further study the byproducts produced by singlet oxygen/chemical reactions -- with an eye toward predicting whether
the byproducts themselves will be toxic. By understanding the stages
of degradation, Minakata and his team can develop an expanded model to
predict the formation of sun-worn byproducts and how the interactions
start again.
Ultimately, a full understanding of the half-lives of the many chemicals
that infiltrate our water sources is a step toward ensuring clean water
for human use.
========================================================================== Story Source: Materials provided by
Michigan_Technological_University. Original written by Kelley
Christensen. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Benjamin Barrios, Benjamin Mohrhardt, Paul V. Doskey, Daisuke
Minakata.
Mechanistic Insight into the Reactivities of Aqueous-Phase Singlet
Oxygen with Organic Compounds. Environmental Science & Technology,
2021; 55 (12): 8054 DOI: 10.1021/acs.est.1c01712 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2021/08/210811113139.htm
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