Ozone Destruction in Aquaculture Applications
(To obtain more information on recirculating aquaculture systems, a complete set of tables, figures and references shown on this and related pages please refer to
the book "Recirculating Aquaculture Systems, 2nd Edition", M. B. Timmons, et al, 2002, Cayuga Aqua Ventures, Ithaca, NY. You can obtain a copy of the
publication from Cayuga Aqua Ventures by visiting their website at www.c-a-v.net.)
Creating an adequate level of residual ozone at the end of the contact chamber to ensure kill-off of bacteria will also
necessitate that this same ozone be removed prior to the water reaching the aquatic organisms. Ozone residuals can be
lethal to fish at ozone concentrations as low as 0.01 mg/L, but the actual concentration depends upon species and life
stage, Table 12.2.(Shown Below)
Due to the acute toxicity of residual ozone to aquatic animals (Wedemeyer et al. 1979), a de-ozonation unit has to be
included. In many cases, residuals are eliminated by water retention within tanks immediately after ozonation, Fig. 12.4,
or by applying small doses of a reducing agent, e.g., sodium thiosulphate. Dissolved ozone can also be stripped into air
when passed through a forced-ventilation packed aeration column, Fig. 12.4.
Air stripping will also remove dissolved oxygen concentrations that are in excess of saturation, which may or may not be
desirable. Dissolved ozone can also be destroyed by passing the water through a biofilter or bed activated carbon,
reaction with low levels of hydrogen peroxide, or contact with high intensity UV-light (catalyzing the conversion of O3 to
O2).
Achieving ozone destruction with UV electromagnetic radiation depends on the wavelength of the UV light source and the
quantity of energy transmitted (Rodriguez and Gagnon, 1991; Hunter et al. 1998). Ozone residuals are destroyed at UV
light wavelengths ranging from 250 to 260 nm. Ironically, UV wavelengths of 185 nm can be used to generate ozone.
The primary ozone treatment components are located on the process pipeline immediately after ozone gas has been
transferred into the water. First, the right hand vessel provides 10 minutes (at 1600 L/min flow) of plug flow contacting to
achieve disinfection. Next, the middle vessel provides 20 minutes (at 1600 L/min flow) of plug flow contacting to achieve
further disinfection and ozone residual destruction. Finally, the left hand vessel (a counter-current, forced-ventilation
column) strips any minor ozone residuals and elevated dissolved oxygen levels immediately before the flow is piped to
the fish culture systems
Ozonation by-products and their toxicity towards aquatic animals are not well described, especially in seawater. More
long-lived reaction products are formed when brackish and seawaters are ozonated. Here, ozone reacts with bromide
ions, and to a lesser extend with chloride ions, to form oxidants toxic to fish and shellfish. The most important are
hypobromous acid (HOBr) and hypobromite ion (OBr-). Both have strong biocidal effects. By prolonged ozonation
hypobromite ion can be further oxidized to bromate (BrO3-), which is a persistent compound. In addition, small amounts
of halogenated organic compounds like bromoform will be formed. Activated carbon filtration has been successfully used
for removal of residual ozone and other oxidants in ozonated seawater (Ozawa et al. 1991).
The off-gas discharged from the transfer unit will contain some ozone if ozone transfer is not 100% efficient. These
ozone containing off-gas discharges may require treatment to destroy remaining ozone. Gas phase ozone destruct
systems are available for this type of application based on thermal or thermal catalytic methods. Ozone destroyers
(decomposers) for gas phase ozone removal can be found by following this link.
(To obtain more information on recirculating aquaculture systems, a complete set of tables, figures and references shown on this and related pages please refer to
the book "Recirculating Aquaculture Systems, 2nd Edition", M. B. Timmons, et al, 2002, Cayuga Aqua Ventures, Ithaca, NY. You can obtain a copy of the
publication from Cayuga Aqua Ventures by visiting their website at www.c-a-v.net.)
Creating an adequate level of residual ozone at the end of the contact chamber to ensure kill-off of bacteria will also
necessitate that this same ozone be removed prior to the water reaching the aquatic organisms. Ozone residuals can be
lethal to fish at ozone concentrations as low as 0.01 mg/L, but the actual concentration depends upon species and life
stage, Table 12.2.(Shown Below)
Due to the acute toxicity of residual ozone to aquatic animals (Wedemeyer et al. 1979), a de-ozonation unit has to be
included. In many cases, residuals are eliminated by water retention within tanks immediately after ozonation, Fig. 12.4,
or by applying small doses of a reducing agent, e.g., sodium thiosulphate. Dissolved ozone can also be stripped into air
when passed through a forced-ventilation packed aeration column, Fig. 12.4.
Air stripping will also remove dissolved oxygen concentrations that are in excess of saturation, which may or may not be
desirable. Dissolved ozone can also be destroyed by passing the water through a biofilter or bed activated carbon,
reaction with low levels of hydrogen peroxide, or contact with high intensity UV-light (catalyzing the conversion of O3 to
O2).
Achieving ozone destruction with UV electromagnetic radiation depends on the wavelength of the UV light source and the
quantity of energy transmitted (Rodriguez and Gagnon, 1991; Hunter et al. 1998). Ozone residuals are destroyed at UV
light wavelengths ranging from 250 to 260 nm. Ironically, UV wavelengths of 185 nm can be used to generate ozone.
The primary ozone treatment components are located on the process pipeline immediately after ozone gas has been
transferred into the water. First, the right hand vessel provides 10 minutes (at 1600 L/min flow) of plug flow contacting to
achieve disinfection. Next, the middle vessel provides 20 minutes (at 1600 L/min flow) of plug flow contacting to achieve
further disinfection and ozone residual destruction. Finally, the left hand vessel (a counter-current, forced-ventilation
column) strips any minor ozone residuals and elevated dissolved oxygen levels immediately before the flow is piped to
the fish culture systems
Ozonation by-products and their toxicity towards aquatic animals are not well described, especially in seawater. More
long-lived reaction products are formed when brackish and seawaters are ozonated. Here, ozone reacts with bromide
ions, and to a lesser extend with chloride ions, to form oxidants toxic to fish and shellfish. The most important are
hypobromous acid (HOBr) and hypobromite ion (OBr-). Both have strong biocidal effects. By prolonged ozonation
hypobromite ion can be further oxidized to bromate (BrO3-), which is a persistent compound. In addition, small amounts
of halogenated organic compounds like bromoform will be formed. Activated carbon filtration has been successfully used
for removal of residual ozone and other oxidants in ozonated seawater (Ozawa et al. 1991).
The off-gas discharged from the transfer unit will contain some ozone if ozone transfer is not 100% efficient. These
ozone containing off-gas discharges may require treatment to destroy remaining ozone. Gas phase ozone destruct
systems are available for this type of application based on thermal or thermal catalytic methods. Ozone destroyers
(decomposers) for gas phase ozone removal can be found by following this link.
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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