SECTION 252:626-9-4. Ozonation

  Ozonation systems may be used in potable water systems for disinfection, oxidation, and microflocculation. Although the installation may be for a specific purpose, such as disinfection, the overall plant design must have the capability to handle ozone by-products created by oxidation and microflocculation. Positive or negative type ozonation systems are allowed. If ozonation is used, it must meet the following:

(1)   Capacity. The production rating of the ozone generators shall be stated in pounds per day and kW-hr per pound at a maximum cooling water temperature and maximum ozone concentration. The design shall ensure that the minimum concentration of ozone in the exit gas shall not be less than one percent (1%) by weight. Ozonation systems shall be sized to have sufficient reserve capacity so that the system does not operate at peak capacity for extended periods of time. The ozone production rate decreases as the temperature of the coolant increases. The design shall ensure that ozone can be produced at the maximum coolant temperature. Backup ozone generating equipment shall be provided.

(2)   Cooling. Adequate cooling shall be provided. The cooling water must be properly treated to minimize corrosion, scaling and microbiological fouling of the water side of the tubes. Where cooling water is treated, cross connection control shall be provided to prevent contamination of the potable water supply.

(3)   Materials. To prevent corrosion, ozone shell and tubes shall be constructed of Type 316L stainless steel.

(4)   Diffusers. A minimum of two contact chambers each equipped with baffles to prevent short circuiting and induce countercurrent flow shall be provided. The diffusion system shall operate so that the ozone is fed at the bottom of the vessel and water is fed at the top of the vessel. Ozone shall be applied using porous-tube or dome diffusers. The minimum contact time shall be ten (10) minutes. A shorter time may occur, only with the approval of the DEQ, if justified by appropriate design and CT Value considerations. Porous diffusers shall not be used when precipitates are formed during ozone applications. The diffuser shall be fully serviceable by either cleaning or replacement.

(5)   Contactors. Contactors shall be separate closed vessels that have no common walls with adjacent rooms. The contactor shall be kept under negative pressure and with sufficient monitors to protect worker safety. The contactor shall be placed where the entire roof is exposed to the open atmosphere. All openings into the contactor for pipe connections, hatchways and/or other openings shall be properly sealed using welds or ozone resistant gaskets. Multiple sampling ports shall be provided to enable sampling of each compartment's effluent water and to confirm CT Value calculations. A pressure or vacuum relief valve shall be provided in the contactor and piped to a location where there will be no damage to the unit. The depth of water in the contactor shall be a minimum of eighteen feet (18') and have a minimum of three feet (3') of freeboard. All contactors shall be equipped so that the contactor can be cleaned, maintained and drained. Each contactor compartment shall be equipped with an access hatchway.

(6)   Ozone destruction unit. A system for treating the final gas-off from each unit shall be provided by either thermal destruction or thermal/catalytic destruction. The maximum ozone concentration in the release is 0.1 ppm by volume. At least two units shall be provided which are each capable of handling the entire gas flow. Exhaust blowers shall be provided in order to draw off-gas to the destruction unit. Catalysts shall be protected from froth, moisture and other impurities. The catalyst and heating elements shall be located to allow for maintenance.

(7)   Piping materials. Only low carbon 304L and 316L stainless steel shall be used for ozone service.

(8)   Joints and connections. Connections on piping used for ozone service shall be welded. Connections with meters, valves or other equipment shall be made with flanged joints with ozone resistant gaskets. A positive closing plug or butterfly valve plus a leak-proof check valve shall be provided in the piping between the generator and the contactor to prevent moisture reaching the generator.

(9)   Instrumentation. Pressure gauges shall be provided at the discharge from the air compressor, at the inlet to the refrigeration 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. Electrical power meters shall be provided for measuring electrical power supplied to the ozone generators. Each generator shall have a automatic shut down when wattage exceeds a preset level. Dew point monitors shall be provided for measuring the moisture of the feed gas from the desiccant dryers. Where there is a potential for moisture to enter the ozone generator from downstream from the unit or where moisture accumulation can occur in the generator during shutdown, post-generator dew point monitors shall be used. Air flow meters shall be provided for measuring air flow from the desiccant dryers to each of the ozone generator and air flow to each contactor, and purge air flow to the desiccant dryers. Temperature gauges shall be provided for the inlet and outlet of the ozone cooling water and the inlet and outlet of the ozone generators feed gas, and when necessary for the inlet and outlet of the ozone power supply cooling water. Water flow meters shall be installed to monitor the flow of cooling water to the ozone generators and when necessary to the ozone power supply. Ozone monitors shall be installed to measure ozone concentration in both feed-gas and off-gas from the contactor and in the off gas from the destruction unit. For disinfection systems, monitors shall also be provided for monitoring ozone residuals in the water. A minimum of one ambient ozone monitor shall be installed in the vicinity of the contactor and a minimum of one shall be installed in the vicinity of the generator. Ozone monitors shall be installed in any area where ozone gas may accumulate.

(10)   Alarms and shut-down systems. Installation of alarms and /or shut-down systems are required. The following alarms and/or shutdown systems shall be installed:

(A)   A dew-point shut-down alarm system, when the generator exceeds 60 degrees Celsius,

(B)   Ozone generator cooling water flow shut-down alarm system for the generator to prevent potential harm,

(C)   Ozone power supply cooling water flow shut-down alarm system, to prevent potential harm to the power supply in the event that cooling water flow decreases to the point that damage to the power supply could occur,

(D)   Ozone generator cooling water temperature shut-down alarm system for the generator when either the inlet or outlet cooling water exceeds a preset temperature,

(E)   Ozone power supply cooling water temperature shut-down alarm system to shut down the power supply if the inlet or outlet cooling water exceeds a certain preset temperature,

(F)   Ozone generator inlet feed-gas temperature shut-down alarm system to the generator if the feed gas temperature is above a preset value,

(G)   Ambient ozone concentration shut-down alarm system shall sound an alarm when the ozone levels in the ambient air exceed 0.1 ppm of ozone and shut down the system when the levels exceed 0.3 ppm of ozone, and

(H)   Ozone destruction temperature alarm system sounding an alarm when the temperature exceeds a preset value.

(11)   Safety. The maximum allowable ozone concentration in the air to which workers may be exposed shall not exceed 0.1 ppm by volume. Emergency exhaust fans shall be installed in rooms containing ozone generators to remove ozone gas. A sign shall be posted stating "No Smoking, Oxygen in Use" at all entrances to the treatment plant. No flammable or combustible materials shall be stored in the oxygen generator areas. The contactor shall be tested for leakage after sealing the exterior.

(12)   Instrumentation. For system used for disinfection CT compliance, provide monitors for ozone residuals in the water with the number and locations of the ozone monitors such that the amount of time that the water is in contact with the ozone residual can be determined.

(13)   Disinfectant residual. The use of ozone as a disinfectant requires the application of a disinfectant capable of maintaining a measurable residual to ensure that bacteriologically safe water is carried throughout the distribution system.

[Source: Added at 18 Ok Reg 1612, eff 6-1-01; Amended at 25 Ok Reg 2304, eff 7-11-08]