Fine Bubble Diffuser Contactors for Ozone Water
Treatment
Ozone contactors with bubble diffusers dissolve ozone into water via a porous
stone (ozone resistant ceramic or in some cases stainless steel) diffuser that
create fine bubbles. As the bubbles rise in the contact vessel they transfer the
ozone into the liquid phase. An advantage of the bubble diffuser contactors is
that they can use the pressure of the ozone generator to drive the gas through
the diffusers without any additional energy input. The off set is the cost to build
the deep basin contactors. Pictures of fine bubble diffusers and contact
chambers are shown below.
The ceramic components are usually held in place with stainless steel hardware
and ozone resistant gaskets (Hypalon. Viton or Teflon). Recently some all
ceramic designs have been offered for sale that eliminate the need for gaskets.
The diffusers can be disks or tubes. Tubular diffusers which are used for air
fed systems have higher gas flow rates which range from 2-6 CFM/diffuser.
Disks or domes which are more often used with oxygen feed have flows of 0.5-2
CFM/diffuser.
The diffusers are located in an array in deep multi chamber basins. The
spacing of the diffusers is important and typically is less than or equal to 4
square feet per diffuser. The arrays are designed to maximize ozone transfer
efficiency. The connecting pipe can be stainless steel or PVC. The submerged
level of the diffuser impacts ozone transfer efficiency. At sea level the diffusers
are typically submerged 16 to 20 feet deep. Different ceramic materials
produce different pressure drops as a function of the gas flow. Transfer
efficiency for air fed ozone generators and bubble contact diffusers is
approximately 85% while for oxygen fed ozone generators feeding high
concentration ozone to bubble diffusers the transfer efficiency can be 95%.
The chambers create a serpentine path for the water to travel with the objective
of creating plug flow through the contactor and maximizing the hydraulic
detention time (minimizing short circuiting of the flow through the contactor). Not
all chambers of the contactor will necessarily have diffuser arrays on the
bottom. In drinking water treatment, where chemical oxidation is the objective
2-4 chambers are used. In drinking water treatment for disinfection, 6-8
chambers are used. If inactivation of Cryptosporidium is needed 10 or more
chambers might be employed.
Bubble diffusers are normally positioned in the first 1-3 chambers of the
contactor. The flow through the chambers with the diffusers can be alternating
counter current/co-current flow or all counter current. Counter current flow
enhances transfer efficiency. Since the first chamber will be exposed to water
with the highest ozone demand, more diffusers should be employed here.
A discussion of bubble diffuser contactors can also be found elsewhere in the
website in a presentation on surface water treatment rules and in a presentation
discussing drinking water plant operations. These papers contain illustrations
and calculations regarding the effectiveness of various designs.
The apparent hydraulic detention time (HDT - the simple geometric volume of
the contact vessel divided by the flow rate through the vessel) is most often not
the effective hydraulic detention time due to short circuiting of the flow through
the vessel. Designers will often use another measure of detention time referred
to as T10. This value represents the time for 90% of the water to pass through
the contact vessel. Typically the value is around 65% of the apparent HDT.
T10 is determined based on results with past designs, sophisticated flow
modeling programs or tracer studies.
Understanding the effective HDT is critical for applications such as disinfection.
To insure the inactivation of micro organisms, certain concentration X time (CT)
values must be achieved. The effective HDT or T10 is used for these
calculations.
The contactor is normally fitted with pressure/vacuum relief valves to prevent
structural damage to the vessel which are made of reinforced concrete.
Contactors are also fitted with ceiling and side wall manholes for inspecting the
diffusers and insuring that the bubble pattern is acceptable and for periodic
replacement of gaskets. Other essential components of the system are sample
ports for measuring ozone residuals in the various chambers, gas flow rate.
Treatment
Ozone contactors with bubble diffusers dissolve ozone into water via a porous
stone (ozone resistant ceramic or in some cases stainless steel) diffuser that
create fine bubbles. As the bubbles rise in the contact vessel they transfer the
ozone into the liquid phase. An advantage of the bubble diffuser contactors is
that they can use the pressure of the ozone generator to drive the gas through
the diffusers without any additional energy input. The off set is the cost to build
the deep basin contactors. Pictures of fine bubble diffusers and contact
chambers are shown below.
The ceramic components are usually held in place with stainless steel hardware
and ozone resistant gaskets (Hypalon. Viton or Teflon). Recently some all
ceramic designs have been offered for sale that eliminate the need for gaskets.
The diffusers can be disks or tubes. Tubular diffusers which are used for air
fed systems have higher gas flow rates which range from 2-6 CFM/diffuser.
Disks or domes which are more often used with oxygen feed have flows of 0.5-2
CFM/diffuser.
The diffusers are located in an array in deep multi chamber basins. The
spacing of the diffusers is important and typically is less than or equal to 4
square feet per diffuser. The arrays are designed to maximize ozone transfer
efficiency. The connecting pipe can be stainless steel or PVC. The submerged
level of the diffuser impacts ozone transfer efficiency. At sea level the diffusers
are typically submerged 16 to 20 feet deep. Different ceramic materials
produce different pressure drops as a function of the gas flow. Transfer
efficiency for air fed ozone generators and bubble contact diffusers is
approximately 85% while for oxygen fed ozone generators feeding high
concentration ozone to bubble diffusers the transfer efficiency can be 95%.
The chambers create a serpentine path for the water to travel with the objective
of creating plug flow through the contactor and maximizing the hydraulic
detention time (minimizing short circuiting of the flow through the contactor). Not
all chambers of the contactor will necessarily have diffuser arrays on the
bottom. In drinking water treatment, where chemical oxidation is the objective
2-4 chambers are used. In drinking water treatment for disinfection, 6-8
chambers are used. If inactivation of Cryptosporidium is needed 10 or more
chambers might be employed.
Bubble diffusers are normally positioned in the first 1-3 chambers of the
contactor. The flow through the chambers with the diffusers can be alternating
counter current/co-current flow or all counter current. Counter current flow
enhances transfer efficiency. Since the first chamber will be exposed to water
with the highest ozone demand, more diffusers should be employed here.
A discussion of bubble diffuser contactors can also be found elsewhere in the
website in a presentation on surface water treatment rules and in a presentation
discussing drinking water plant operations. These papers contain illustrations
and calculations regarding the effectiveness of various designs.
The apparent hydraulic detention time (HDT - the simple geometric volume of
the contact vessel divided by the flow rate through the vessel) is most often not
the effective hydraulic detention time due to short circuiting of the flow through
the vessel. Designers will often use another measure of detention time referred
to as T10. This value represents the time for 90% of the water to pass through
the contact vessel. Typically the value is around 65% of the apparent HDT.
T10 is determined based on results with past designs, sophisticated flow
modeling programs or tracer studies.
Understanding the effective HDT is critical for applications such as disinfection.
To insure the inactivation of micro organisms, certain concentration X time (CT)
values must be achieved. The effective HDT or T10 is used for these
calculations.
The contactor is normally fitted with pressure/vacuum relief valves to prevent
structural damage to the vessel which are made of reinforced concrete.
Contactors are also fitted with ceiling and side wall manholes for inspecting the
diffusers and insuring that the bubble pattern is acceptable and for periodic
replacement of gaskets. Other essential components of the system are sample
ports for measuring ozone residuals in the various chambers, gas flow rate.
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
Ozone Water Treatment - Fine Bubble Diffusers for Mixing
