Wisconsin Administrative Code
Department of Natural Resources
NR 800 - Environmental Protection - Water Supply
Chapter NR 811 - Requirements For The Operation And Design Of Community Water Systems
Subchapter VII - Treatment
Section NR 811.54 - Ozonation

Universal Citation: WI Admin Code ยง NR 811.54

Current through August 26, 2024

Ozonation can be used for a variety of purposes including disinfection, oxidation, and microflocculation. When applied, all of these reactions may occur but typically only one is the primary purpose for its use. Ozonation can be used for the removal of color, taste and odors, organics, algae, cyanide, hydrogen sulfide, iron, manganese, and heavy metals. In addition to these treatment processes, ozone is an acceptable alternative to chlorine disinfectants. Given the sophisticated nature of the ozone process, consideration shall be given to the need for maintaining qualified operators to operate and maintain the equipment. The following requirements shall be met:

(1) GENERAL. The following general requirements shall be met:

(a) All process designs shall be based on bench or pilot scale studies of dosage requirements, application points, and detention times conducted in accordance with s. NR 811.44.

(b) When ozone is used as a disinfectant, ozonation and detention shall provide the required disinfection CT value. Additionally, application of a disinfectant which maintains a measurable residual in the distribution system shall be required.

(c) Where ozonation is approved by the department to be used for disinfection of a bacteriologically unsafe water supply, duplicate process streams shall be provided. This includes air supply, air preparation equipment, ozone generators, ozone contact chambers, ozone diffusers, power supply, and post disinfection equipment. This requirement may be waived by the department where other acceptable water sources having sufficient capacity are available.

(2) FEED GAS PREPARATION. Feed gas can be air, oxygen enriched air, or high purity oxygen. Sources of high purity oxygen include purchased liquid oxygen; on site generation using cryogenic air separation; or temperature, pressure or vacuum swing, adsorptive separation, technology. For high purity oxygen-feed systems, dryers typically are not required. Feed gas preparation shall meet the following requirements:

(a) Air handling equipment. Air handling equipment on conventional low pressure air-feed systems shall consist of an air compressor unless drawn by vacuum, water or air separator, refrigerant and desiccant dryers and particulate filters. For oxygen-feed systems, compressors, separators, and dryers may not be required by the department depending on the purity of the oxygen. In all cases the design shall ensure that the maximum dew point of -60°C (-76°F) will not be exceeded at any time.

(b) Air compression.
1. Air compressors shall be of the liquid-ring or rotary lobe, oil-less, positive displacement type for smaller systems or dry rotary screw compressors for larger systems.

2. The air compressors shall have the capacity to simultaneously provide for maximum ozone demand, provide the air flow required for purging the desiccant dryers, where required, and allow for standby capacity.

3. Air feed for the compressor shall be drawn from a point protected from rain, snow, condensation, mist, and fog to minimize moisture content of the air supply. The air feed shall be protected from contaminated air sources. Outside air intakes shall consist of a downturned pipe elbow installed at a location least susceptible to vandalism and covered with a 24-mesh corrosion resistant screen.

4. A compressed air after-cooler or entrainment separator or both with automatic drain shall be provided prior to the dryers to reduce the water vapor.

(c) Air drying.
1. Dry, dust-free, and oil-free feed gas shall be provided to the ozone generator. Sufficient drying to a maximum dew point of -60°C (-76°F) shall be provided at the end of the drying cycle.

2. Drying for high pressure systems shall be accomplished using desiccant dryers. For low pressure systems, a refrigeration air dryer in series with desiccant dryers shall be used.

3. A refrigeration dryer capable of reducing the inlet air temperature to 4°C (40°F) shall be provided for low pressure air preparation systems. The dryer may be of the compressed refrigerant type or chilled water type.

4. The desiccant dryers shall be of the external heated or heatless type.

5. For heat-reactivated desiccant dryers, the unit shall contain 2 desiccant filled towers complete with pressure relief valves, 2 4-way valves and a heater. In addition, external type dryers shall have a cooler unit and blowers. The size of the unit shall be such that the specified dew point will be achieved during a minimum absorption cycle time of 16 hours while operating at the maximum expected moisture loading conditions.

6. Each dryer shall be capable of venting dry gas to the atmosphere, prior to the ozone generator, to allow start-up when other dryers are on-line.

(d) Air filters.
1. Air filters shall be provided on the suction side of the air compressors, between the air compressors and the dryers and between the dryers and the ozone generators.

2. The filter before the compressor shall be of the coalescing type and be capable of removing all particles larger than 10 microns in diameter. The filter before the dryer shall be of the coalescing type and be capable of removing all particles larger than 0.3 microns in diameter. The filter after the dryer shall be of the particulate type and be capable of removing all particles larger than 0.1 microns in diameter or a size specified by the generator manufacturer.

(e) Air preparation piping. Piping in a compressed air preparation system shall be common grade steel, seamless copper, stainless steel, or galvanized steel. The piping shall be designed to withstand the maximum pressures in the air preparation system. PVC piping may be used in a vacuum air preparation system when located and supported to be protected from physical damage including from heat.

(3) OZONE GENERATORS. Ozone generators shall meet the following requirements:

(a) Capacity. The production rating of the ozone generators shall be provided in pounds per day and pounds per kilowatt-hour. The capacity of any ozone generators shall be determined by ozone demand tests including tests under critical conditions. Where ozone is approved for use by the department as a disinfectant, the generators shall be sized in conjunction with the detention basins to provide the required inactivation CT values for viruses, Giardia lamblia, and Cryptosporidium contained in ss. NR 810.59, 810.60, and 810.61.
1. The design shall ensure that the minimum concentration of ozone in the generator exit gas will be 1.0% by weight.

2. Generators shall be sized to have sufficient reserve capacity so that the system does not operate at peak capacity for extended periods of time. Low, medium, and high frequency systems which operate at lower peak voltages require less reserve capacity.

3. Generators with individual dielectrics shall have the capability of operating satisfactorily while individual dielectrics are out-of-service. This shall be accomplished through the use of individually fused dielectrics.

4. At least 2 generators, each with a capacity of supplying the normal ozone demand, shall be provided. If determined by the department to be not critical to maintaining production capacity, smaller installations employing ozone generators with multiple individually fused dielectrics may be able to employ a fewer number of generators each having excess ozone production capacity.

5. If there is to be a variation in the supply temperature of the generator cooling water throughout the year, then curves or other data shall be furnished to the department to show ozone production changes due to the varying temperature of the supplied cooling water. The design shall ensure that the generators can produce the required ozone at the maximum coolant temperature.

(b) Electrical. The generators may be low, medium, or high frequency type. The specifications shall require that the transformers and other electrical hardware be proven, high quality components designed for ozone service.

(c) Cooling. Adequate cooling shall be provided. Cooling water supplied to the ozone generators may not be corrosive or scale forming and shall be sufficiently free of microbiological and inorganic contaminants to prevent fouling of the water side of the tubes. If natural water quality does not meet this requirement, treatment shall be required. A closed loop cooling water system shall be used if proper cooling water conditions cannot be assured.

(d) Materials. To prevent corrosion, the ozone generator shell and tubes shall be constructed of type 304L or 316L stainless steel.

(4) OZONE CONTACTORS. The selection or design of the contactor and method of ozone application depends on the purpose for which the ozone is being used. Contactors can be of the diffused bubble, venturi, or aspirating turbine mixer type as approved by the department. Ozone contactors shall meet the following requirements:

(a) Where ozone is used as a disinfectant, a minimum of 2 contact chambers shall be provided with the chambers designed to prevent short-circuiting. Contactors shall be closed vessels.

(b) Contactors shall be separate vessels having no common walls with the remainder of the facility, unless common walls are approved by the department on a case-by-case basis. If common walls are used, the contactor shall be kept under negative pressure and sufficient ozone monitors shall be provided to protect worker safety. No normally inhabited structure may be constructed over an ozone contactor or reservoir containing ozone.

(c) Contact vessels shall be made of reinforced poured concrete. All reinforcement bars shall be covered with a minimum of 1.5 inches of concrete. Ozone resistant interior coatings shall be approved by the department in accordance with s. NR 810.09 (5). Smaller contact vessels may be made of stainless steel, fiberglass, or other material which will be stable in the presence of residual ozone and ozone in the gas phase above the water level.

(d) Contact chambers shall be of sufficient depth and size to allow for adequate contact time and freeboard for foaming where applicable. The depth of water in bubble diffuser contactors shall normally be a minimum of 18 feet unless a shallower depth can be justified to the department. A minimum freeboard of 3 feet shall be provided where foaming will be an issue.

(e) The contact time for disinfection shall be determined based on the required inactivation CT values for viruses, Giardia lamblia, and Cryptosporidium contained in ss. NR 810.59, 810.60, and 810.61. The minimum contact time shall be 10 minutes. A shorter contact time may be approved by the department if justified by appropriate design and CT considerations. Sufficient ozone capacity and contact chamber size shall be provided to achieve the desired CT value when injecting ozone into only one of the 2 contact chambers. The diffusion system shall normally work on a countercurrent basis such that the ozone shall enter through porous diffusers at the bottom of the vessel and water shall enter from the top of the vessel. Countercurrent flow shall be provided in all chambers of the vessels. Co-current diffusion systems shall only be approved by the department where adequate justification can be supplied.

(f) For ozone applications in which precipitates are formed, such as with iron and manganese removal, porous diffusers may not be used.

(g) Where taste and odor control is of concern, multiple application points and contactors shall be considered.

(h) A system shall be provided between the contactor and the off-gas destruct unit to remove foam from the air and return the froth to the contactor or other location acceptable to the department when foam will be an issue. A potable water spray system shall be placed in the contactor head space if foaming is expected to be excessive.

(i) All openings into the contactor for pipe connections, hatchways, etc., shall be properly sealed to prevent the escape of ozone using welds or ozone resistant gaskets such as Teflon or Hypalon.

(j) A pressure or vacuum relief valve shall be provided in the contactor as appropriate. Pressure or vacuum relief valve discharge piping shall be piped to a location where there will be no damage to the ozone destruction unit or an uncontrolled release of ozone.

(k) Sampling faucets and monitors shall be provided on the inlet and outlet of each contact chamber to monitor water quality and the ozone residual. If allowed by the department, a portable monitor or a comparable testing method may be used to analyze water collected from sample taps provided on the inlet and outlet of each contact chamber.

(l) A water meter shall be provided on the inlet to the contact chambers to measure water flow.

(m) If required by the department, contactors or reservoirs used as contactors shall be fitted with the improvements necessary to allow sampling of water from intermediate points for ozone residual.

(n) All contactors shall have provisions for cleaning, maintenance, and drainage. Each contactor compartment shall also be equipped with an access hatchway.

(5) OZONE DESTRUCTION. Ozone destruction shall meet the following requirements:

(a) A method or combination of methods for destroying or recirculating the final off gas from the ozone contactors shall be provided to meet safety and air quality standards. Acceptable methods include:
1. Thermal destruction.

2. Catalytic destruction.

3. Thermal and catalytic destruction.

4. Recycling to some point in the treatment system in addition to the installation of destruction equipment.

(b) A detectable ozone residual may not carry over into the distribution system.

(c) The maximum allowable air ozone concentration in the destruction unit discharge is 0.1 ppm by volume.

(d) At least 2 units shall be provided which are each capable of handling the entire gas flow unless the second unit is deemed unnecessary by the department.

(e) Exhaust blowers shall be provided in order to draw ozone off-gas from the contactors into the destruct unit.

(f) Catalysts shall be protected from foam, moisture and other impurities that may harm the catalyst.

(g) The catalyst and heating elements shall be located where they can be easily reached for maintenance.

Note: In order to reduce the risk of fires, the use of units that operate at lower temperatures is encouraged, especially where high purity oxygen is the feed gas.

(6) PIPING MATERIALS. Piping materials used in ozone service shall meet the following requirements:

(a) Only low carbon 304L and 316L stainless steel piping shall be used for ozone service. Alternative piping materials may be approved by the department on a case-by-case basis.

(b) Gasket materials shall be Teflon or Hypalon.

(c) Rubber components may not be used in contact with ozone.

(7) JOINTS AND CONNECTIONS.

(a) Connections on stainless steel piping used for ozone service are to be welded where possible.

(b) Connections with meters, valves, or other equipment are to be made with flanged joints with ozone resistant gaskets, such as Teflon or Hypalon. Screwed fittings and field-cut threaded connections may not be used.

(c) A positive closing plug or butterfly valve and a leak-proof backflow prevention check valve system shall be provided in the piping between the generator and the contactor for pressurized ozone generation systems.

(8) INSTRUMENTATION. Instrumentation shall meet the following requirements:

(a) Pressure gauges shall be provided at the discharge from the air compressor, at the inlet to the refrigerator dryers, at the inlet and outlet of the desiccant dryers, at the inlet to the ozone generators and contactors, and at the inlet to the ozone destruction unit.

(b) Each generator shall have a trip which shuts down the generator when the wattage exceeds a preset level. It is recommended that electric power meters be provided for measuring the electric power supplied to the ozone generators.

(c) Dew point monitors shall be provided for measuring the moisture of the feed gas from each desiccant dryer. Where there is potential for moisture entering the ozone generator from downstream of the unit or where moisture accumulation can occur in the generator during shutdown, post-generator dew point monitors shall be used.

(d) Air flow meters shall be provided for measuring the air flow from the desiccant dryers to each of the ozone generators, the air flow to each contactor, and the purge air flow to the desiccant dryers.

(e) Temperature gauges shall be provided for the inlet and outlet of the ozone cooling water and the inlet and outlet of the ozone generator feed gas, and, if applicable, for the inlet and outlet of the ozone power supply cooling water.

(f) Water flow meters shall be installed to monitor the flow of cooling water to the ozone generators and, if applicable, to the ozone power supply.

(g) At a minimum, ozone monitors shall be installed and maintained to measure ozone concentrations in both the feed-gas and the off-gas from the contactor and the off-gas from the destruct unit. Monitors or a comparable testing method shall also be provided for measuring ozone residuals in water in accordance with subs. (4) and (5) (b). The number and location of ozone residual monitors shall be such that the amount of time that the water is in contact with the ozone residual can be determined.

(h) Ambient air ozone monitors shall be installed in rooms where exposure to ozone is possible.

(9) ALARMS. The installation of alarm and shutdown systems shall meet the following requirements:

(a) A dew point alarm and shutdown shall shut down the generator in the event the system dew point exceeds -60°C (-76°F).

(b) An ozone generator cooling water flow alarm and shutdown shall shut down the generator in the event that cooling water flows decrease to the point that generator damage could occur.

(c) An ozone power supply cooling water flow alarm and shutdown shall shut down the power supply in the event that cooling water flow decreases to the point that power supply damage could occur.

(d) An ozone generator cooling water temperature alarm and shutdown shall shut down the generator if either the inlet or outlet cooling water exceeds the designated preset temperature.

(e) An ozone power supply cooling water temperature alarm and shutdown shall shut down the power supply if either the inlet or outlet cooling water exceeds the designated preset temperature.

(f) An ozone generator inlet feed-gas temperature alarm and shutdown shall shut down the generator if the feed-gas temperature exceeds the designated preset value.

(g) An ambient air ozone concentration alarm and shutdown shall sound when the ozone level in the building ambient air exceeds 0.1 ppm or a lower value chosen by the water supplier. Ozone generator shutdown shall automatically occur when the building ambient air ozone level exceeds 0.3 ppm or a lower value chosen by the water supplier.

(h) An ozone destruct temperature alarm shall sound when the temperature exceeds the designated preset value.

(i) Audible alarms and warning lights shall be installed and maintained to insure operators are alerted to improper operating or hazardous conditions.

(10) SAFETY.

(a) The maximum allowable ozone concentration in the air to which workers may be exposed may not exceed 0.1 ppm by volume.

(b) Noise levels resulting from the operation of the ozonation system shall be controlled to within acceptable limits by special room construction and equipment isolation.

(c) High voltage and high frequency electrical equipment shall meet current electrical and fire codes.

(d) An exhaust fan shall be provided in the ozone generation and contactor rooms to remove ozone gas if a leak occurs and shall meet all of the following requirements:
1. One complete air change per minute shall be provided when the room is occupied.

2. The exhaust fan suction shall be located near the floor with the point of discharge located to avoid contamination of air inlets to other rooms and structures, to outside breathable air, or being blocked by snow or other obstructions.

3. Air inlets shall be located near the ceiling and controlled to prevent adverse temperature variations.

4. An exhaust fan switch shall be located outside of the entrance to the room with a signal light indicating fan operation when the fan can be controlled from more than one point.

(e) A portable purge air blower that will remove residual ozone in the contactor prior to entry for repair or maintenance shall be provided.

(f) A sign shall be posted indicating "No smoking, oxygen in use" at all entrances to the treatment plant. In addition, no flammable or combustible materials shall be stored within the oxygen generator areas.

Disclaimer: These regulations may not be the most recent version. Wisconsin may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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