Section 58.01.16.500 - FACILITY AND DESIGN STANDARDS FOR MUNICIPAL WASTEWATER TREATMENT OR DISPOSAL FACILITIES: DISINFECTION01.General. Disinfection of the effluent shall be provided as necessary to meet applicable standards. The design of new municipal wastewater treatment facilities, or municipal wastewater treatment facilities undergoing material modifications, shall consider meeting both the bacterial standards and the disinfectant residual limit in the effluent. The disinfection process shall be selected after due consideration of waste characteristics, type of treatment process provided prior to disinfection, waste flow rates, pH of waste, disinfectant demand rates, current technology application, cost of equipment and chemicals, power cost, and maintenance requirements as determined in the preliminary engineering report. Where a disinfection process other than chlorination, ultraviolet disinfection, or ozone is proposed, supporting data from pilot plant installations or similar full scale installations shall be required as a basis for the design of the system.02.Determining the Necessity For Disinfection of Sewage Wastewater Treatment Plant Effluent. a. Disinfection of municipal wastewater treatment facility effluent shall be required when: i. Required by an NPDES permit; orii. The effluent is discharged to a land application/reuse facility and is required to meet the disinfection requirements found in IDAPA 58.01.17, "Recycled Water Rules."iii. The effluent discharged to a land application/reuse facility, where ground water contamination has exceeded the bacterial limit found in IDAPA 58.01.11, "Ground Water Quality Rules," and it has been determined by the Department that disinfection is required.b. The need for disinfection of sewage wastewater treatment plant effluent where treatment consists of lagoons with at least thirty (30) day retention time shall be evaluated on a case by case basis.03.Chlorine Disinfection.a. Type. Chlorine is available for disinfection in gas, liquid (hypochlorite solution), and pellet (hypochlorite tablet) form. The type of chlorine should be carefully evaluated during the facility planning or preliminary engineering process. The use of chlorine gas or liquid will be most dependent on the size of the facility and the chlorine dose required. Large quantities of chlorine, such as are contained in ton cylinders and tank cars, can present a considerable hazard to plant personnel and to the surrounding area should such containers develop leaks. Both monetary cost and the potential public exposure to chlorine shall be considered when making the final determination.b. Dosage. For disinfection, the capacity shall be adequate to produce an effluent that will meet the applicable bacterial limits specified by the regulatory agency for that installation. Required disinfection capacity will vary, depending on the uses and points of application of the disinfection chemical. The chlorination system shall be designed on a rational basis and calculations justifying the equipment sizing and number of units shall be submitted for the whole operating range of flow rates for the type of control to be used. System design considerations shall include the controlling wastewater flow meter (sensitivity and location), telemetering equipment, and chlorination controls.c. Piping and Connections. Piping systems shall be as simple as practicable, specifically selected and manufactured to be suitable for chlorine service, with consideration for minimizing number of joints. Piping should be well supported and protected against temperature extremes. Venting of excess gas shall be provided. Special considerations shall be given to piping and fixture selection for hypochlorite and chlorine use. Section 008 provides a reference to guidance documents; see Subsections 008.01, 008.04 and 008.05.d. Standby Equipment and Spare Parts. Standby equipment of sufficient capacity should be available to replace the largest unit during shutdowns. Spare parts shall be available for all disinfection equipment to replace parts which are subject to wear and breakage.e. Housing. i. Feed and Storage Rooms. Gas chlorination equipment and chlorine cylinders shall be housed in a building. If this building is used for other purposes, a gas-tight room shall separate this equipment from any other portion of the building. Floor drains from the chlorine room shall not be connected to floor drains from other rooms. Doors to this room shall open only to the outside of the building and shall be equipped with panic hardware. Rooms shall permit easy access to all equipment. Section 009 provides a reference to requirements of other regulatory entities, compliance with which may be required by other law.ii. Ventilation. Section 009 provides a reference to the requirements of the National Electric Code, compliance with which may be required by other law.iii. Electrical Controls. Section 009 provides a reference to the requirements of the National Electric Code, compliance with which may be required by other law.iv. Protective and Respiratory Gear. Respiratory air-pac protection equipment shall be available where chlorine gas is handled, and shall be stored at a convenient location, but not inside any room where chlorine is used or stored. Instructions for using the equipment shall be posted. Section 008 provides a reference to guidance documents; see Subsections 008.01, 008.04 and 008.05.04.Dechlorination. a. Types.i. Dechlorination of wastewater effluent may be necessary to reduce the toxicity due to chlorine residuals. The most common dechlorination chemicals are sulfur compounds, particularly sulfur dioxide gas or aqueous solutions of sulfite or bisulfite. Pellet dechlorination systems are also available for small facilities.ii. The type of dechlorination system should be carefully selected considering criteria including the following: type of chemical storage required, amount of chemical needed, ease of operation, compatibility with existing equipment, and safety.b. Dosage. The dosage of dechlorination chemical depends on the residual chlorine in the effluent, the final residual chlorine limit, and the particular form of the dechlorinating chemical used.c. Standby Equipment and Spare Parts. The same requirements apply as for chlorination systems. See Subsection 500.04.d.d. Housing Requirements/Feed and Storage Rooms. The requirements for housing SO2 gas equipment shall follow the same guidelines as used for chlorine gas. Refer to Subsection 500.04.e. for specific details. When using solutions of the dechlorinating compounds, the solutions may be stored in a room that meets the safety and handling requirements set forth in Subsection 450.07. The mixing, storage, and solution delivery areas must be designed to contain or route solution spillage or leakage away from traffic areas to an appropriate containment unit.e. Protective and Respiratory Gear. The respiratory air-pac protection equipment is the same as for chlorine. See Subsection 500.04.e. (Refer to The Compressed Gas Association Publication CGA G-3-1995, "Sulfur Dioxide.")05.Ultraviolet (UV) Radiation. a. The following documents are recommended to be used as references for UV system sizing and facility design: i. "Wastewater Engineering, Treatment and Reuse," Metcalf and Eddy, referenced in Section 008.ii. For reuse applications, "Ultraviolet Disinfection Guidelines for Drinking Water and Water Reuse," National Water Research Institute/AWWA Research Foundation, referenced in Section 008.b. For UV systems to be installed at any existing wastewater treatment facility, collection of one (1) year's worth of UV transmittance (UVT) data (four (4) times per day) prior to predesign is encouraged, especially for facilities larger than five million gallons per day (5 mgd) (design peak hour flow), and facilities that have industries that vary discharge throughout the year.c. The preliminary engineering report for all UV disinfection facilities shall include the following: i. A minimum of two (2) open channels (or justification for using a smaller system).ii. A minimum of two (2) banks of UV lamps per channel (or justification for using a smaller system).iii. Description of the redundancy provided.iv. Description of the upstream flow splitting device (which splits flow to the two (2) or more UV channels).v. Description of water level control device.vi. Description of method used to take a channel off-line for maintenance, and method to dewater a channel.vii. Type of UV system technology (low-pressure low-intensity, low-pressure high-intensity, medium pressure, etc.), with consideration given to power consumption.viii. Summary of UVT data and collimated beam data.ix. Description of HVAC system requirements to ensure adequate UV system performance during summer peak temperature period.x. Description of maintenance requirements including removal (cleaning) of biofilms from the channel walls upstream and downstream of the UV system.xi. General description of alarming and controls.xii. Description of procedure used for UV system sizing.xiii. Design criteria:(3) Design water temperature range.(5) End of lamp life factor.(7) Quartz sleeve transmittance factor.(8) Design peak hour flow.(9) Existing minimum flow.(11) Disinfection requirements (coliform concentration).(12) Maximum head-loss from upstream of the first bank to downstream of the last bank of lamps (lamp spacing divided by two (2)).d. Use of bioassay method of UV system sizing is encouraged if all manufacturers under consideration have existing bioassays performed using identical protocol, and the bioassay was performed under conditions similar to the design application. Use of the bioassay method of UV system sizing is discouraged if the conditions of Subsection 500.05.d. cannot be met.e. Closed chamber units will be reviewed on a case by case basis in accordance with Subsection 450.03.b.06.Ozone. Ozone systems for disinfection shall be evaluated on a case-by-case basis. Design of these systems shall be based upon experience at similar full scale installations or thoroughly documented prototype testing with the particular wastewater.Idaho Admin. Code r. 58.01.16.500