Section NR 110.23 - Disinfection(1) GENERAL. (a)Applicability. Disinfection shall be provided in accordance with WPDES permit requirements.(b)Effluent limitations.1. When chlorine is used as the disinfectant, the residual concentration in the wastewater treatment facility effluent shall comply with WPDES permit requirements.2. Effluent bacterial concentrations shall conform with WPDES permit requirements.(c)Process selection.1. The selection of the method of disinfection shall be based on a cost effective comparison of disinfection methods.2. Where a disinfection process other than chlorine is proposed, supporting data from pilot plant installations or similar full-scale installations shall be submitted as a basis for the design of the system in accordance with s. NR 110.15(1).(2) DISINFECTION WITH CHLORINE. (a)Storage requirements.1. If a gas chlorinator and chlorine cylinders are installed in a building used for other purposes, the chlorinator and chlorine cylinders shall be separated from all other portions of the building by being kept in a gas-tight room. Doors to this room shall open only to the outside of the building, and shall be equipped with panic or emergency hardware. Those rooms shall be at or slightly above grade and must permit easy access to all equipment. If one ton or larger cylinders of chlorine are used, the chlorination equipment shall be kept in a room separate from the chlorine cylinders.2. A clear glass, gas-tight window shall be installed in an exterior door or interior wall of the chlorinator room to permit the chlorinator to be viewed without entering the room.3. Chlorinator and chlorine cylinder storage rooms shall be provided with a means of heating so that a temperature of at least 16°C (60°F) can be maintained. The rooms shall be protected against temperatures exceeding 65°C (140°F).4. Forced, mechanical ventilation of the chlorinator room and the chlorine storage room shall be installed. Ventilation equipment shall be capable of providing one complete air change per minute. The entrance to the air exhaust duct from the room shall be near the floor and the point of discharge shall be so located as not to contaminate the air inlet to any buildings or inhabited areas. Air inlets shall be so located as to provide cross ventilation and at such a temperature that will not adversely affect the chlorination equipment. The vent hose from the chlorinator shall discharge to the outside atmosphere above grade.5. The controls for the ventilator and lights shall be such that the ventilator and lights will automatically operate when the door is opened but must be manually switched off even if the door closes. Switches shall also be provided to allow manual operation of the lights and ventilator from outside of the room without opening the door.6. One ton cylinders shall be used at treatment facilities where the chlorine use rate exceeds 68 kilograms (150 pounds) per day.(b)Feed equipment.1. Solution-feed vacuum type chlorinators or positive displacement type hypochlorite feeders shall be used.2. An ample supply of water shall be supplied for operating the chlorinator.3. Chlorinators and feed equipment shall be sized to handle the maximum design chlorine demand.4. Chlorinators shall be equipped to provide control of chlorine application through the full range of design chlorine demand. If necessary, more than one rotometer shall be supplied to ensure control of chlorine application through the design range.5. Scales or other means of determining chlorine usage shall be provided. Scales shall be of corrosion-resistant material.6. Evaporators for converting liquid chlorine to a gas may be used if necessary.(c)Piping and connections.1. Only piping systems specifically manufactured for chlorine service shall be used.2. Due to the corrosiveness of wet chlorine, all lines designed to handle dry chlorine shall be protected from the entry of water or air containing water.(d)Chlorine control systems. In all systems with an average design flow of greater than 945 cubic meters per day (0.25 million gallons per day), the chlorine feed mechanism shall be provided with either an automatic flow proportional control or an automatic residual control. Chlorine residual analyzers shall be located near the chlorine contact tank. The total response time for automatic residual control systems may not exceed 3 minutes.(e)Application.1. The chlorine shall be mixed as rapidly as possible. This may be accomplished by either the design of a turbulent flow regime or the use of a mechanical flash mixer.2. A chlorine contact tank shall be provided and shall be sized to provide a detention time of 60 minutes at average design flow or 30 minutes at maximum hour design flow.3. Chlorine contact tanks shall be baffled to provide a flow channel with a minimum length to width ratio of 40:1.4. The department may approve contact tanks which do not comply with the requirements of this paragraph. Such facilities, however, shall be field tested to demonstrate that short circuiting of hydraulic flow through the contact chamber does not occur.(f)Dechlorination.1. Dechlorination shall be provided in accordance with WPDES permit requirements.2. Dechlorination chemicals shall be rapidly mixed with the effluent.3. Sulfur dioxide dechlorination systems shall be designed in the same manner as chlorination systems.4. Effluent reaeration shall be provided after dechlorination if necessary to insure adequate dissolved oxygen concentration in the receiving stream.5. Dechlorinated effluent shall be monitored for chlorine residual and dissolved oxygen in accordance with WPDES permit requirements.(g)Safety equipment.1. Respiratory air-pack protection equipment, meeting the requirements of the national institute for occupational safety and health (NIOSH) shall be available where chlorine gas is handled, and shall be stored at a convenient location. The equipment may not be stored inside any room in which chlorine is used and stored. The equipment shall use compressed air or oxygen, have at least a 30-minute capacity, and be compatible with the units used by the fire department having jurisdiction over the plant.2. A plastic bottle of ammonium hydroxide shall be provided for the detection of chlorine leaks.3. Leak repair kits shall be provided when one ton chlorine cylinders are used.(3) ULTRAVIOLET DISINFECTION. Provisions shall be made to clean ultraviolet units without loss of disinfection. This shall be accomplished by installing multiple ultraviolet units, by providing ultrasonic cleaners, or by providing an effluent holding tank with a capacity of one hour detention at average design flow.Wis. Admin. Code Department of Natural Resources NR 110.23
Cr. Register, November, 1974, No. 227, eff. 12-1-74; r. and recr. Register, March, 1978, No. 267, eff. 4-1-78; r. and recr. Register, February, 1983, No. 326, eff. 3-1-83; CR 09-123: am. (2) (d) and (e) 2. Register July 2010 No. 655, eff. 8-1-10.