UV Ozone Advanced Oxidation Process
In the UV ozone process, photons in the UV spectrum ozone in the presence of water to oxygen and peroxide. The
peroxide then reacts with the ozone to form the hydroxyl radical. A simplified reaction sequence is shown below;
O3 + H2O → O2 + H2O2 (in the presence of UV light)
2 O3 + H2O2 → 2 •OH + 3 O2
Organic oxidation occurs due to the reaction with hydroxyl radicals, molecular ozone and direct photolysis.
The major components of an O3/UV system include: UV lamps, lamp sleeves, and lamp cleaning system, ozone generator
and diffusers, ozone contactor, ozone off-gas decomposer, oxygen or air feed systems, supply and discharge pumps and
piping, monitoring and control systems. Since ozone absorbs UV light at 254 nm, low pressure UV (LPUV) lamps are used
(see a brief discussion of UV lamps for water treatment).
The two primary design variables that must be optimized in sizing a UV AOP system are the UV power radiation per unit
volume of water treated — more commonly referred to as UV dose — and the concentration of hydrogen peroxide or
ozone. UV dose, when applied to AOP, is a measure of the total lamp electrical energy applied to a fixed volume of water.
The units are measured in kWh/1,000 gallons treated. This parameter combines flow rate, residence time and light
intensity into a single term. The dose of UV light and peroxide/ozone required per unit volume of water treated may vary
depending on the water to be treated.
The advantages and disadvantages of the O3/UV system are:
The removal efficiency of the combined O3/UV process is typically higher than the additive removal efficiencies of ozone
and UV alone.
The combined O3/UV process is more efficient at generating hydroxyl radicals than the combined H2O2/UV process for
equal oxidant concentrations using LP-UV. This is because the molar extinction coefficient of O3 at 254 nm is two orders
of magnitude greater than that of H2O2, indicating that a lower UV intensity or a higher H2O2 dose is required to
generate the same number of hydroxyl radicals for these two processes. However, for MP-UV lamps, H2O2/UV processes
will generate more hydroxyl radicals than O3/UV processes.
Despite the fact that O3/UV is more stoichiometrically efficient at generating hydroxyl radicals than H2O2/UV or H2O2/O3,
the O3/UV process is less energetically efficient than H2O2/UV or H2O2/O3 for generating large quantities of hydroxyl
radicals due to the low solubility of O3 in water compared to H2O2. Thus, operational costs are expected to be
higher. The hydroxyl radical yield can be decreased further by the presence of interfering parameters (e.g., nitrates,
turbidity, or iron) in the source water.
Gaseous O3 must be diffused into the source water, resulting in potential mass transfer limitations relative to H2O2,
which is fed as a liquid solution.
UV light penetration into the source water can be adversely affected by turbidity. There are also many interference
compounds that absorb UV light (e.g., nitrate and iron) and, thus, reduce process efficiency. UV lamp and sleeve failures
can potentially contaminate treated water with mercury.
In the UV ozone process, photons in the UV spectrum ozone in the presence of water to oxygen and peroxide. The
peroxide then reacts with the ozone to form the hydroxyl radical. A simplified reaction sequence is shown below;
O3 + H2O → O2 + H2O2 (in the presence of UV light)
2 O3 + H2O2 → 2 •OH + 3 O2
Organic oxidation occurs due to the reaction with hydroxyl radicals, molecular ozone and direct photolysis.
The major components of an O3/UV system include: UV lamps, lamp sleeves, and lamp cleaning system, ozone generator
and diffusers, ozone contactor, ozone off-gas decomposer, oxygen or air feed systems, supply and discharge pumps and
piping, monitoring and control systems. Since ozone absorbs UV light at 254 nm, low pressure UV (LPUV) lamps are used
(see a brief discussion of UV lamps for water treatment).
The two primary design variables that must be optimized in sizing a UV AOP system are the UV power radiation per unit
volume of water treated — more commonly referred to as UV dose — and the concentration of hydrogen peroxide or
ozone. UV dose, when applied to AOP, is a measure of the total lamp electrical energy applied to a fixed volume of water.
The units are measured in kWh/1,000 gallons treated. This parameter combines flow rate, residence time and light
intensity into a single term. The dose of UV light and peroxide/ozone required per unit volume of water treated may vary
depending on the water to be treated.
The advantages and disadvantages of the O3/UV system are:
The removal efficiency of the combined O3/UV process is typically higher than the additive removal efficiencies of ozone
and UV alone.
The combined O3/UV process is more efficient at generating hydroxyl radicals than the combined H2O2/UV process for
equal oxidant concentrations using LP-UV. This is because the molar extinction coefficient of O3 at 254 nm is two orders
of magnitude greater than that of H2O2, indicating that a lower UV intensity or a higher H2O2 dose is required to
generate the same number of hydroxyl radicals for these two processes. However, for MP-UV lamps, H2O2/UV processes
will generate more hydroxyl radicals than O3/UV processes.
Despite the fact that O3/UV is more stoichiometrically efficient at generating hydroxyl radicals than H2O2/UV or H2O2/O3,
the O3/UV process is less energetically efficient than H2O2/UV or H2O2/O3 for generating large quantities of hydroxyl
radicals due to the low solubility of O3 in water compared to H2O2. Thus, operational costs are expected to be
higher. The hydroxyl radical yield can be decreased further by the presence of interfering parameters (e.g., nitrates,
turbidity, or iron) in the source water.
Gaseous O3 must be diffused into the source water, resulting in potential mass transfer limitations relative to H2O2,
which is fed as a liquid solution.
UV light penetration into the source water can be adversely affected by turbidity. There are also many interference
compounds that absorb UV light (e.g., nitrate and iron) and, thus, reduce process efficiency. UV lamp and sleeve failures
can potentially contaminate treated water with mercury.
Spartan Environmental Technologies
Air and Water Treatment
Air and Water Treatment
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Spartan Environmental
Technologies, L.L.C.
7383 Lauren J Dr
Mentor, OH 44060
USA
Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com
Technologies, L.L.C.
7383 Lauren J Dr
Mentor, OH 44060
USA
Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com