PURPOSE: This rule specifies the minimum standards for the design of disinfection processes that are part of wastewater collection and treatment systems. This rule is to be used with rules 10 CSR 20-8.110 through 10 CSR 20-8.210. It does not address all aspects of design, and the design engineer may refer to other appropriate reference materials so long as these minimum standards set forth in this rule are met.

1. (1) Applicability. Wastewater systems that utilize disinfection shall be designed based on criteria contained in this rule, published standards, applicable federal and state requirements, standard textbooks, current technical literature, and applicable safety standards. In the event of any conflict between the above criteria, the requirement in this rule shall prevail.

   1. (A) This rule shall not apply to treatment units covered in 10 CSR 20-8.300.
   2. (B) This rule shall not apply to treatment units covered in 10 CSR 20-8.500.

2. (2) General.

   1. (A) Emergency Power. Disinfection and dechlorination processes, when used, shall be provided during all power outages. For additional emergency power requirements, refer to the provisions listed in 10 CSR 20- 8.140(7).
   2. (B) Secondary containment. Secondary containment shall comply with the provisions listed in 10 CSR 20-8.140(9)(A)2.

3. (3) Chlorine Disinfection.

   1. (A) Contact period. A minimum contact period of fifteen (15) minutes at design peak hourly flow or maximum rate of pumpage shall be provided after thorough mixing.

   2. (B) Gaseous Chlorine Housing.

      1. 1. Feed and storage rooms shall—

         1. A. Have chlorine gas feed and storage

rooms constructed of fire and corrosion resistant material;

1. B. Provide a gas-tight room to sepa-

rate equipment from any other portion of the building if gas chlorination equipment or chlorine cylinders are to be in a building used for other purposes;

1. C. Have smooth floor surfaces that

are chemical resistant, impervious, and slip resistant. Floor drains are discouraged. Design floor drains, where provided, with the ability to be plugged and sealed;

1. D. Have doors to this room that only

open to the outside of the building, and are equipped with panic hardware. Provide door locks to prevent unauthorized access, but do not need a key to exit the locked room using the panic hardware;

1. E. Be well-lit with lights that are

sealed so that they will continue working during a chlorine leak. Comply with 10 CSR 20- 8.140(7)(B), requirements for Class I, Division 2, Group D locations when selecting lighting and electrical equipment;

1. F. Be at ground level and permit easy

access to all equipment;

1. G. Separate storage areas for one- (1-)

ton cylinders from the feed area; and

1. H. Have designated areas for “full”

and “empty” cylinder storage.

1. 2. Heating and cooling.

   1. A. Rooms containing disinfection

equipment shall be provided with a means of heating and cooling so that a temperature of at least sixty degrees Fahrenheit (60° F) and no more than eighty-six degrees Fahrenheit (86°F) can be maintained.

1. B. Heating or air conditioning equip-

ment provided for the chlorinator room shall be separate from central heating and air conditioning systems to prevent chlorine gas from entering the central system and central heating or cooling ducts are not allowed to terminate or pass through a chlorinator room.

1. 3. Ventilation shall conform to the fol-

lowing:

1. A. Install forced mechanical ventila-

tion to provide one (1) complete fresh air change per minute when the chlorinator room is occupied. Construct fans of chemical resistant materials and have chemical proof motors. Squirrel cage type fans located outside the chlorinator room may be approved if the fan housings and ducting are airtight and made of chlorine and corrosion resistant material;

1. B. Locate the entrance to the air

exhaust duct from the room no more than twelve inches (12") off the floor. Locate the point of discharge as not to contaminate the air inlet to any buildings or present a hazard at the access to the chlorinator room or other inhabited areas. Utilize louvers for air exhaust to facilitate airtight closure;

1. C. Locate air inlets as to provide

cross ventilation. Place the outside air inlet at least three feet (3') above grade. Utilize louvers for air inlets to facilitate airtight closure; and

1. D. Position the vent hose from the

chlorinator to the outside atmosphere above grade. Provide passive vent screens.

1. 4. Electrical controls. Switches for fans

and lights shall be outside of the chlorinator room at the entrance.

1. 5. Protective and respiratory gear.

Where chlorine gas is present the applicant shall comply with 10 CSR 20-8.140(9)(D)1.

1. (C) Alarm System. The applicant shall conform to 10 CSR 20-8.140(7)(C) and be responsible for specifying what the alarm requirements are necessary to assure consistent disinfection in compliance with the applicable bacteria limits and the disinfection residual limit in the effluent.
2. (D) Sampling Equipment. Sampling equipment shall be consistent with the requirements in 10 CSR 20-8.140(7)(F).

1. (4) Dechlorination.

   1. (A) Containers. Dilution tanks and mixing tanks are required when using dry compounds and may be necessary when using liquid compounds to deliver the proper dosage.

   2. (B) Mixing and Contact Requirements.

      1. 1. Mixing requirements. Solid dechlori-

nation systems shall not be located in the chlorine contact tank.

1. 2. Contact time. A minimum of thirty

1. (30) seconds for mixing and contact time shall be provided at the design peak hourly flow or maximum rate of pumpage.

   1. (C) Housing Requirements.

      1. 1. Feed and storage rooms. The require-

ments for housing sulfite gas equipment shall follow the same guidelines as for chlorine gas. For specific details follow the provisions listed in subsection (3)(B).

1. 2. Protective and respiratory gear. See

paragraph (3)(B)5. of this rule.

1. (D) Alarm System. See subsection (3)(C) of this rule.
2. (E) Sampling Equipment. Sampling equipment shall be consistent with the requirements in 10 CSR 20-8.140(7)(F).

1. (5) Ultraviolet Disinfection.

   1. (A) Dosage and System Sizing.

      1. 1. General. The UV dosage shall be

based on the design peak hourly flow, maximum rate of pumpage, or peak batch flow.

1. 2. Batch discharges. If no flow equaliza-

tion is provided for a batch discharger, the dosage shall be based on the peak batch flow.

1. 3. Bioassay. The UV system shall deliv-

er the target dosage based on equipment derating factors and, if needed, have the UV equipment manufacturer verify that the scale up or scale down factor utilized in the design is appropriate for the specific application under consideration.

1. 4. The design delivered UV dosage for a

wastewater treatment facility shall be a minimum of thirty thousand microwatt seconds per centimeters squared (30,000 μW • s/cm2) based on MS-2 phage inactivation.

1. (B) Design.

   1. 1. Open channel systems. The combina-

tion of the total number of banks shall be capable of treating the design peak hourly flow, maximum rate of pumpage, or peak batch flow.

1. 2. Closed vessel systems. The combina-

tion of the total number of closed vessels shall be capable of treating the design peak hourly flow, maximum rate of pumpage, or peak batch flow.

1. 3. Cleaning. Closed vessel systems uti-

lizing medium-pressure lamps shall be provided with an automatic cleaning system in order to prevent algae growth.

1. (C) Monitoring and Alarms.

   1. 1. The UV system must continuously

monitor and display at the UV system control panel the following minimum conditions:

1. A. The relative intensity of each bank

or closed vessel system;

1. B. The operational status and condi-

tion of each bank or closed vessel system;

1. C. The ON/OFF status of each lamp

in the system; and

1. D. The total number of operating

hours of each bank or each closed vessel system.

1. 2. The UV system shall include an

alarm system. Alarm systems shall comply with 10 CSR 20-8.140(7)(C).

1. (D) Electrical Controls. For electrical controls, follow the provisions listed in 10 CSR 20-8.140(7)(B) for electrical controls requirements.
2. (E) Sampling Equipment. Sampling equipment shall be consistent with the requirements in 10 CSR 20-8.140(7)(F).

AUTHORITY: section 644.026, RSMo 2016.* Original rule filed Aug. 10, 1978, effective March 11, 1979. Amended: Filed June 15, 2018, effective Feb. 28, 2019. *Original authority: 644.026, RSMo 1972, amended 1973, 1987, 1993.