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 con-

structed of fire and corrosion resistant material;

1. B. Provide a gas-tight room to separate 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 resis-

tant, 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 out-

side 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 equip-

ment;

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 equipment 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 following:

   1. A. Install forced mechanical ventilation to provide one

1. (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 dechlorination systems shall

not be located in the chlorine contact tank.

1. 2. Contact time. A minimum of thirty (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 requirements 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 equalization is provided

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

1. 3. Bioassay. The UV system shall deliver 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 treat-

ment 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 combination 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 combination 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 utilizing medium-pres-

sure 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 condition of each bank or

closed vessel system;

1. C. The ON/OFF status of each lamp in the system; and
2. 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.