1. (a) Pretreatment.

   1. (1) Pretreatment to remove grit, debris, and excess oil and grease must precede an rotating biological contractor (RBC) unit.
   2. (2) A design may require primary clarifiers, fine screens, or grit removal chambers to control high levels of grease, oil, grit, or other debris in the influent waste stream.
   3. (3) A RBC unit must include pre-aeration if influent has a high hydrogen sulfide concentration.

2. (b) Enclosures and Ventilation.

   1. (1) An RBC unit must be covered and provide appropriate levels of ventilation.
   2. (2) A cover must have working clearance of at least 30 inches above an RBC unit, unless the cover can be removed with on-site equipment.
   3. (3) Enclosures must be constructed of a corrosion resistant material.

   4. (4) An RBC unit must include:

      1. (A) access doors on each end, and
      2. (B) observation ports with covers at 3.0 foot intervals along the RBC unit.

3. (c) Media Design.

   1. (1) An RBC unit must provide self-cleaning action for the media.
   2. (2) RBC media must be compatible with the wastewater to be treated.
   3. (3) An RBC design using multiple stages must use low-density media for the first stage.

4. (d) Design Flexibility. If included in the design of an RBC, the report must include descriptions of the following:

   1. (1) controlled flow to multiple first stages;
   2. (2) alternate flow and staging arrangements;
   3. (3) removable baffles between stages; and
   4. (4) provision for step feed and supplemental aeration.

5. (e) Tank Configuration. A design must ensure that an RBC tank:

   1. (1) minimizes the zones in which solids will settle out; and
   2. (2) includes tank drains to facilitate removal of any accumulated solids.
6. (f) Control of Unwanted Growth in the Initial Stages. Chlorine may be added upstream of an RBC system to control the growth of beggiatoa.

7. (g) Maintenance Provisions.

   1. (1) An RBC system designed for 1.0 million gallons per day (mgd) or greater must have two or more process trains consisting of three or more stages in series in each process train.
   2. (2) Each process train must be capable of being removed from service when maintenance or cleaning is required.
8. (h) Bearing Maintenance. An RBC system's bearings must be easily accessible for inspection and lubrication.

9. (i) Organic Loading Design Requirements.

   1. (1) A design must be based on the organic loading for an RBC system on total five-day biochemical oxygen demand (BOD₅) in the waste.
   2. (2) The maximum loading rate must not exceed 8.0 pounds of BOD₅ per day per 1,000 square feet (sf) of media in any stage.
   3. (3) A design must require the RBC media area be adjusted to compensate for the effects of the ratio of soluble BOD₅ to total BOD₅.

   4. (4) Allowable organic loading for the entire RBC system must not exceed:

      1. (A) 3.0 lbs of BOD₅ per day per 1,000 sf of media area for facilities required to meet secondary treatment; or
      2. (B) 2.0 lbs of BOD₅ per day per 1,000 sf for a facility required to meet advanced secondary treatment.
10. (j) Hydraulic Loading Design Requirements. An RBC system must include flow equalization when the peak-to-design flow ratio is higher than 2.5 to 1.0 to prevent loss of fixed growth from the media.

11. (k) Stages.

    1. (1) An RBC system designed for a BOD₅ removal unit must have at least three stages in series, unless the report justifies a lesser number using operational data from either a full-scale operating facility or pilot unit with an appropriate scale-up factor.
    2. (2) The first stage of an RBC system must include a means of spreading the influent flow evenly across the media.

12. (l) Drive Systems. An RBC drive system must handle the maximum anticipated media load and may be a variable speed system. An RBC unit may be mechanically driven or air driven.

    1. (1) Mechanical Drive.

       1. (A) A mechanical drive must have a motor and speed control unit capable of maintaining the required revolutions per minute.
       2. (B) A fully assembled spare for each size mechanical drive unit must be on-site.

    2. (2) Air Drive.

       1. (A) Each RBC unit must have air diffusers mounted below the media and off-center from the vertical axis of the RBC unit and must have air cups mounted on the outside of the media to collect the air.

       2. (B) The blowers must provide the capacity to supply adequate airflow for:

          1. (i) each RBC unit;
          2. (ii) double the airflow rate to any one unit while the others are running normally; and
          3. (iii) the required airflow with the largest blower out of service.

       3. (C) The air diffuser pipe to each unit must:

          1. (i) be mounted so that the air diffuser pipe may be removed without draining the tank or without moving the RBC media; and
          2. (ii) include an air control valve to each RBC unit.

13. (m) Dissolved Oxygen.

    1. (1) An RBC system must maintain a minimum dissolved oxygen concentration of 1.0 milligram per liter in all stages during the maximum organic loading rate.
    2. (2) The executive director may require supplemental aeration.

Source Note:The provisions of this §217.185 adopted to be effective August 28, 2008, 33 TexReg 6843.