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Wastewater Treatment And Ozone
Ozone Water
Treatment Disadvantages
By John
Brennan
Often
wastewater and sewage contain a bewildering array of germs and carbon-based or
organic chemicals and pollutants.
Removing
germs and organic compounds is a critical part of wastewater treatment, and
ozone is one of the chemicals often employed to do the job.
While
it's more effective than chlorine at destroying germs, it does have some
important disadvantages.
Solubility
and Activity
If the dose of ozone is too low, some of the germs and
especially those that can form cysts may survive.
Consequently,
higher ozone concentrations are beneficial.
These
are difficult to maintain, however, because ozone is 12 times less soluble in
water than chlorine, so the maximum disinfectant concentrations you can reach
are much lower when you use ozone.
Moreover,
ozone breaks down very rapidly, and the higher the temperature or the pH, the
more rapidly it decays.
If
the water is rich in organic compounds or suspended solids, a lot of the ozone
may be consumed through reactions with these other contaminants, leaving an insufficient
amount available to destroy germs.
That's
why ozone is not an economical option for wastewater with very high amounts of
suspended solids or total organic compounds.
Reactivity
Ozone's reactivity is what makes it such a great
disinfectant. That same strength, however, comes with some accompanying
disadvantages.
Ozone
can react with many metals, including those used to line wastewater treatment
containers, so operators must use corrosion-resistant materials like stainless steel, which makes plant construction more
expensive.
Moreover,
ozone's reactivity makes it a toxic chemical, so operators must design plants
in such a way that workers don't come into contact with ozone gas escaping from
the water.
This
too increases the expense of ozone wastewater treatment.
Expense
Ozone is more challenging to produce and deliver than
chlorine.
Typically,
plant operators generate ozone by running an electric current through air
passing between two electrodes, a technique called corona discharge.
About
85 percent of the energy input to a corona discharge system is wasted in the
form of heat.
This
method is extremely energy-intensive and the equipment required is more
complicated than chlorination systems, meaning that ozone generation is
typically more expensive than the alternatives.
Residuals
and Byproducts
When ozone reacts with organic compounds, it creates a
variety of byproducts.
If
the water contains bromide ions, ozone treatment can form brominated compounds
like the bromate ion, which is a possible human carcinogen.
Consequently,
operators must either control the pH or avoid use of ozone if the water is rich
in bromide salts.
Finally,
ozone is unlike chlorine in that there is no residual or remaining disinfectant
once the process is over; any ozone that doesn't react with contaminants breaks
down completely.
This
makes it more difficult for plant operators to keep tabs on how well
disinfection is working since there is no residual level of ozone in the water
that they can monitor.
About the
Author
Based in San Diego, John
Brennan has been writing about science and the environment since 2006. His
articles have appeared in "Plenty," "San Diego Reader,"
"Santa Barbara Independent" and "East Bay Monthly." Brennan
holds a Bachelor of Science in biology from the University of California, San
Diego.
https://sciencing.com/ozone-water-treatment-disadvantages-22555.html
https://sciencing.com/ozone-water-treatment-disadvantages-22555.html
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