Section 58.01.08.530 - DISINFECTION OF DRINKING WATER, DISINFECTING AGENTSPWS owners may accomplish with gas and liquid chlorine, calcium or sodium hypochlorites, chlorine dioxide, ozone, or ultraviolet light. Other disinfecting agents will be considered, providing reliable application equipment is available and testing procedures for a residual are recognized in "Standard Methods for the Examination of Water and Wastewater," referenced in Subsection 002.02, or an equivalent means of measuring effectiveness exists. The required amount of primary disinfection needed will be specified by the Department. Consideration must be given to the formation of disinfection by-products (DBP) when selecting the disinfectant. See Section 531, Design Standards for Chemical Application. For PWSs using only groundwater and that voluntarily chlorinate, see Subsection 552.04.
01.Chlorination. a. In addition to the requirements of Section 531, chlorination equipment must meet the following requirements: i. Solution-feed gas chlorinators or hypochlorite feeders of the positive displacement type must be provided.ii. Standby or backup equipment of sufficient capacity will be available to replace the largest unit. Spare parts will be on hand to replace parts subject to wear and breakage.iii. Automatic proportioning chlorinators are required where the rate of flow or chlorine demand is not reasonably constant.iv. Each eductor (submerged jet pump) must be selected for the point of application with particular attention given to the quantity of chlorine to be added, the maximum injector waterflow, the total discharge back pressure, the injector operating pressure, and the size of the chlorine solution line.v. The chlorine solution injector/diffuser must be compatible with the point of application to provide a rapid and thorough mix with all the water being treated.vi. Automatic switch-over of chlorination treatment units will be provided, where necessary, to assure continuous disinfection.b. Effective contact time and point of application requirements are as follows:i. Effective contact time sufficient to achieve the inactivation of target pathogens under the expected range of raw water pH and temperature variation must be demonstrated through tracer studies or other evaluations or calculations acceptable to the Department. Improving Clearwell Design for CT Compliance, referenced in Section 002.02, contains information that may be used as guidance for these calculations. Additional baffling can be added to new or existing basins to minimize short circuiting and increase contact time.ii. At least two (2) contactors must be provided which are each capable of providing the required effective contact time at one-half (1/2) of the plant design capacity. Alternatively, a single contactor that can provide effective contact time at plant design capacity may be designed with separate sections and bypass piping to allow sections to be cleaned or maintained individually during low flow conditions. Any PWS that produces water on an irregular schedule may provide documentation for the Department's review and approval that a single contactor is an acceptable design by demonstrating there is adequate time for maintenance and cleaning during operation shutdowns.iii. At plants treating surface water, except slow sand filtration systems: Unless otherwise approved by the Department, in addition to the injection point prior to the disinfection contact tank, injection points, including all appurtenant chemical feed piping, must also be provided for applying the disinfectant to the raw water, settled water, and water entering the distribution system.iv. For pipeline contactors, provision must be made to drain accumulated sediment from the bottom of the contactor if the discharge from the contactor is not located at the bottom.c. Chlorine residual test equipment recognized in the "Standard Methods for the Examination of Water and Wastewater," referenced in Subsection 002.02, must be provided for use by the operator. All surface water treatment plants that serve a population greater that three thousand three hundred (3,300) must have equipment to measure chlorine residuals continuously entering the distribution system. A sample tap must be provided to measure chlorine residual and will be located at a point after receiving the required contact time and at or prior to the first service connection.d. Chlorinator piping requirements:i. The chlorinator water supply piping must be designed to prevent contamination of the treated water supply by sources of questionable quality. At all facilities treating surface water, pre-and post-chlorination systems must be independent to prevent possible siphoning of partially treated water into the clear well. The water supply to each eductor must have a separate shut-off valve. No master shut-off valve will be allowed.ii. The pipes carrying elemental liquid or dry gaseous chlorine under pressure must be Schedule 80 seamless steel tubing or other materials recommended by the Chlorine Institute (never use PVC). Rubber, PVC, polyethylene, or other materials recommended by the Chlorine Institute must be used for chlorine solution piping and fittings. Nylon products are not acceptable for any part of the chlorine solution piping system.02.Disinfection with Ozone. PWSs that are required to maintain a disinfectant residual in the distribution system must supplement ozone disinfection with a chemical disinfectant. a. The following are requirements for feed gas preparation: i. Feed gas can be air, oxygen enriched air, or high purity oxygen. Sources of high purity oxygen include purchased liquid oxygen conforming with AWWA Standard B-304; on site generation using cryogenic air separation; or temperature, pressure or vacuum swing (adsorptive separation) technology. In all cases, the design engineer must ensure that the maximum dew point of -76°F (-60°C) will not be exceeded at any time.ii. Air compression: (1) Air compressors will 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 will 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 will be drawn from a point protected from rain, condensation, mist, fog and contaminated air sources to minimize moisture and hydrocarbon content of the air supply.(4) A compressed air after-cooler, entrainment separator, or a combination of the two (2) with automatic drain will be provided prior to the dryers to reduce the water vapor.(5) A back-up air compressor must be provided so that ozone generation is not interrupted in the event of a break-down.iii. Air drying: (1) Dry, dust-free and oil-free feed gas must be provided to the ozone generator. Dry gas is essential to prevent formation of nitric acid, to increase the efficiency of ozone generation and to prevent damage to the generator dielectrics. Sufficient drying to a maximum dew point of -76°F (-60°C) must be provided at the end of the drying cycle.(2) Drying for high pressure systems may be accomplished using heatless desiccant dryers only. For low pressure systems, a refrigeration air dryer in series with heat-reactivated desiccant dryers will be used.(3) A refrigeration dryer capable of reducing inlet air temperature to 40°F (4°C) will be provided for low pressure air preparation systems. The dryer can be of the compressed refrigerant type or chilled water type.(4) For heat-reactivated desiccant dryers, the unit must contain two (2) desiccant filled towers complete with pressure relief valves, two (2) four-way valves and a heater. In addition, external type dryers must have a cooler unit and blowers. The size of the unit will be such that the specified dew point will be achieved during a minimum adsorption cycle time of sixteen (16) hours while operating at the maximum expected moisture loading conditions.(5) Multiple air dryers will be provided so that the ozone generation is not interrupted in the event of dryer breakdown.(6) Each dryer will be capable of venting "dry" gas to the atmosphere, prior to the ozone generator, to allow start-up when other dryers are "on-line."iv. Air filters: (1) Air filters will 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 desiccant dryers will be of the coalescing type and be capable of removing aerosol and particulates larger than 0.3 microns in diameter. The filter after the desiccant dryer will be of the particulate type and be capable of removing all particulates greater than 0.1 microns in diameter, or smaller if specified by the generator manufacturer.v. Piping in the air preparation system can be common grade steel, seamless copper, stainless steel or galvanized steel. The piping must be designed to withstand the maximum pressures in the air preparation system.b. The following requirements apply to the ozone generator: i. Capacity. (1) The production rating of the ozone generators must be stated in pounds per day and kWhr per pound at a maximum cooling water temperature and maximum ozone concentration.(2) The design will ensure that the minimum concentration of ozone in the generator exit gas will not be less than one (1) percent (by weight).(3) Generators will be sized to have sufficient reserve capacity so that the PWS does not operate at peak capacity for extended periods of time resulting in premature breakdown of the dielectrics.(4) The production rate of ozone generators will decrease as the temperature of the coolant increases. If there is to be a variation in the supply temperature of the coolant throughout the year, then pertinent data will be used to determine production changes due to the temperature change of the supplied coolant. The design will ensure that the generators can produce the required ozone at maximum coolant temperature.(5) Appropriate ozone generator backup equipment must be provided.ii. The generators can be low, medium or high frequency type. Specifications will require that the transformers, electronic circuitry and other electrical hardware be proven, high quality components designed for ozone service.iii. Adequate cooling must 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 must be provided to prevent contamination of the potable water supply.iv. To prevent corrosion, the ozone generator shell and tubes must be constructed of Type 316L stainless steel.c. The following requirements apply to ozone contactors: i. Bubble diffusers. (1) Where disinfection is the primary application, a minimum of two (2) contact chambers, each equipped with baffles to prevent short circuiting and induce countercurrent flow, will be provided. Ozone must be applied using porous-tube or dome diffusers.(2) The minimum contact time will be ten (10) minutes. A shorter contact time (CT) may be approved by the Department if justified by appropriate design and "CT" considerations.(3) Where taste and odor control is of concern, multiple application points and contactors will be considered.(4) Contactors will be separate closed vessels that have no common walls with adjacent rooms. The contactor must be kept under negative pressure and sufficient ozone monitors will be provided to protect worker safety.(5) Contact vessels can be made of reinforced concrete, 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. If contact vessels are made of reinforced concrete, all reinforcement bars must be covered with a minimum of one and one-half (1.5) inches of concrete.(6) Where necessary, a system is to be provided between the contactor and the off-gas destruct unit to remove froth from the air and return the other to the contactor or other location acceptable to the Department. If foaming is expected to be excessive, then a potable water spray system must be placed in the contactor head space.(7) All openings into the contactor for pipe connections, hatchways, etc. must be properly sealed using welds or ozone resistant gaskets such as Teflon or Hypalon.(8) Multiple sampling ports must be provided to enable sampling of each compartment's effluent water and to confirm "CT" calculations.(9) A pressure/vacuum relief valve must be provided in the contactor and piped to a location where there will be no damage to the destruction unit.(10) The depth of water in bubble diffuser contactors must be a minimum of eighteen (18) feet. The contactor must also have a minimum of three (3) feet of freeboard to allow for foaming.(11) All contactors will have provisions for cleaning, maintenance and drainage of the contactor. Each contactor compartment must also be equipped with an access hatchway.(12) Aeration diffusers must be fully serviceable by either cleaning or replacement.ii. Other contactors, such as the venturi or aspirating turbine mixer contactor, may be approved by the Department provided adequate ozone transfer is achieved and the required contact times and residuals can be met and verified.d. The following requirements apply to ozone destruction units:i. A system for treating the final off-gas from each contactor must be provided in order to meet safety and air quality standards. Acceptable systems include thermal destruction and thermal/catalytic destruction units.ii. The maximum allowable ozone concentration in the discharge is 0.1 ppm (by volume).iii. At least two (2) units will be provided which are each capable of handling the entire gas flow.iv. Exhaust blowers must be provided in order to draw off-gas from the contactor into the destruct unit.v. Catalysts must be protected from froth, moisture and other impurities which may harm the catalyst.vi. The catalyst and heating elements will be located where they can easily be reached for maintenance.e. Only low carbon 304L and 316L stainless steels may be used for ozone service with 316L preferred.f. The following requirements apply to joints and connections:i. Connections on piping used for ozone service are to be welded where possible.ii. 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 may not be used because of their tendency to leak.iii. A positive closing plug or butterfly valve plus a leak-proof check valve must be provided in the piping between the generator and the contactor to prevent moisture reaching the generator.g. The following instrumentation must be provided:i. Pressure gauges 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.ii. A trip which shuts down the generator when the wattage exceeds a certain preset level.iii. Dew point monitors for measuring the moisture of the feed gas from the desiccant dryers. 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 must be used.iv. Air flow meters for measuring air flow from the desiccant dryers to each of the other ozone generators, air flow to each contactor, and purge air flow to the desiccant dryers.v. Temperature gauges for the inlet and outlet of the ozone cooling water and the inlet and outlet of the ozone generator feed gas and, if necessary, for the inlet and outlet of the ozone power supply cooling water.vi. Water flow meters to monitor the flow of cooling water to the ozone generators and, if necessary, to the ozone power supply.vii. Ozone monitors to measure zone concentration in both the feed-gas and off-gas from the contactor and in the off-gas from the destruct unit. For disinfection systems, monitors for monitoring ozone residuals in the water. The number and location of ozone residual monitors must be such that the amount of time that the water is in contact with the ozone residual can be determined.viii. A minimum of one ambient ozone monitor installed in the vicinity of the contactor and a minimum of one installed in the vicinity of the generator. Ozone monitors must be installed in any areas where ozone gas may accumulate.h. Safety requirements are as follows: i. The maximum allowable ozone concentration in the air to which workers may be exposed must not exceed one-tenth part per million (0.1 ppm) by volume.ii. Noise levels resulting from the operating equipment of the ozonation system must be controlled to within acceptable limits by special room construction and equipment isolation.iii. PWS owners must provide emergency exhaust fans in the rooms containing the ozone generators to remove ozone gas if leakage occurs.iv. PWS owners must post a sign indicating "No smoking, oxygen in use" at all entrances to the treatment plant. In addition, no flammable or combustible materials may be stored within the oxygen generator areas.03.Disinfection with Chlorine Dioxide. Chlorine dioxide may be considered as a primary and residual disinfectant, a pre-oxidant to control tastes and odors, to oxidize iron and manganese, and to control hydrogen sulfide and phenolic compounds. When choosing chlorine dioxide, consideration must be given to formation of the regulated by-products, chlorite and chlorate. a. Chlorine dioxide generation equipment must be factory assembled pre-engineered units with a minimum efficiency of ninety-five (95) percent. The excess free chlorine may not exceed three (3) percent of the theoretical stoichiometric concentration required.b. Other design requirements include: i. The design must comply with all applicable portions of Subsections 530.01.a. through 530.01.d.ii. The maximum residual disinfectant level allowed is zero point eight (0.8) milligrams per liter (mg/1), even for short term exposures.iii. Notification of a change in disinfection practices and the schedule for the changes must be made known to the public; particularly to hospitals, kidney dialysis facilities and fish breeders, as chlorine dioxide and its by-products may have effects similar to chloramines.04.Other Disinfecting Agents. Proposals for use of disinfecting agents other than those listed must be submitted to the Department for approval in the preliminary engineering report required under Section 503.Idaho Admin. Code r. 58.01.08.530