Design of Sodium Hypochlorite (NaClO) Disinfection and Sodium Bisulfite (NaHSO₃) Dechlorination Systems

1. (a) Redundancy. A Sodium Hypochlorite (NaClO) and Sodium Bisulfate (NaHSO₃) system must include at least two chemical solution pumps and must ensure that the capacity requirements of §217.272(b) of this title (relating to Capacity and Sizing of Chlorine (Cl₂) Disinfection and Sulfur Dioxide (SO₂) Dechlorination Systems) are met with the largest pump out of service.

2. (b) Capacity and Sizing. The size of a chemical liquid solution pump and pipe system must be determined as follows:

   1. (1) NaClO.

      1. (A) Determine Pounds Per Day of Chlorine (Cl₂) Required. Figure: 30 TAC §217.272(b), Table K.1. and Figure: 30 TAC §217.272(a), Equation K.1. of this title must be used to determine the pounds per day of Cl₂ required.
      2. (B) Cl₂ Determination. The pounds of available Cl₂ per gallon of NaClO solution must be determined using values and appropriate references supplied by chemical manufacturer.
      3. (C) Gallons per Hour Determination. In order to size the chemical metering equipment, the gallons per hour must be calculated using the values found in the following equation:
         Attached Graphic
         

   2. (2) NaHSO₃.

      1. (A) Figure: 30 TAC §217.280(b)(1)(C), Equation K.4. of this subsection must be the basis to determine the pounds per day of chemical required.
      2. (B) The minimum amount of NaHSO₃ needed to dechlorinate one pound of Cl₂ is 1.465 pounds. The pounds per day of Cl₂ that must be dechlorinated, as determined in subparagraph (A) of this paragraph, multiplied by 1.465 pounds of NaHSO₃ per pound of Cl₂, determines the pounds of NaHSO₃ needed.
      3. (C) The gallons per hour (R) of NaHSO₃ solution needed from the chemical metering equipment must be calculated using the following equation:
         Attached Graphic
         
3. (c) Dosage Control. A dosage control system may be positive pressure or vacuum and must automatically adjust the NaClO or NaHSO₃ feed rate to correspond to the flow of the effluent stream.

4. (d) Chemical Handling.

   1. (1) Storage Tank Sizing.

      1. (A) A bulk storage facility for NaClO with a solution strength greater than or equal to 10% must not be sized to store more than a 15-day supply, unless a residual analyzer or oxidation-reduction potential (ORP) monitor provides automatic feed control to compensate for solution degradation.
      2. (B) For NaClO with a solution strength less than 10%, and where a residual analyzer or ORP monitor is provided, a bulk storage facility must not be sized to store more than a 30-day supply.
      3. (C) A facility with a design flow equal to or greater than 1.0 million gallons per day must have at least two chemical storage tanks.

   2. (2) Temperature considerations.

      1. (A) If a NaClO tank is not stored indoors, the tank must be opaque or otherwise block sunlight penetration.
      2. (B) An outdoor NaHSO₃ storage facility and pipes must be insulated and heat traced in a location where the ambient temperature is below 40 degrees F, based on the lowest 7-day average of the average daily local temperatures over the last 10-years, as measured at the nearest National Oceanic and Atmospheric Administration's National Weather Service weather station.

5. (e) Equipment and Materials.

   1. (1) Equipment and materials used for storage, pumping, and transport of NaClO must be used according to the manufacturer's recommendations and suitable for use in a corrosive chemical environment.
   2. (2) Equipment and materials used for storage, pumping, and transport of NaHSO₃ must be used according to the manufacturer's recommendations and suitable for use in an acidic chemical environment.

6. (f) Safety.

   1. (1) Ventilation. A chemical storage area must be sufficiently ventilated to prevent buildup of fumes.
   2. (2) Liquid-depth indicators. A storage tank must have an external liquid-depth indicator.

   3. (3) Spill containment.

      1. (A) A chemical storage area must have secondary containment equal to 125% of the volume of the largest storage tank.
      2. (B) A manifolded tank must have secondary containment equal to 125% of the cumulative manifolded tank volume, unless the pipe system prevents a combined release.

      3. (C) A tank must be placed on an equipment pad that is:

         1. (i) elevated above the secondary containment maximum liquid level; or
         2. (ii) provided with positive drainage from below the tank.
      4. (D) A containment system for NaClO must be separate from a containment system for NaSO₃.
   4. (4) Emergency and Protective Equipment. A chemical storage area must have at least one emergency eyewash station and adequate personal protective equipment for all facility staff working in the area.

Source Note:The provisions of this §217.280 adopted to be effective August 28, 2008, 33 TexReg 6843.