1. (a) Inlets.

   1. (1) A clarifier must have an inlet valve or gate.
   2. (2) A clarifier inlet must provide uniform flow and stilling.
   3. (3) A transfer pipe must not trap or entrain air.
   4. (4) Vertical flow velocity through an inlet stilling well must not exceed 0.15 feet per second at peak flow.
   5. (5) An inlet distribution channel must prevent the settling of solids in the channel.

2. (b) Scum removal.

   1. (1) A clarifier must include scum baffles and a means for the collection and disposal of scum.
   2. (2) Scum collected from a clarifier in a facility using an activated sludge process and an aerated lagoon may be discharged to an aeration basin or digester, or may use another disposal method that complies with Chapter 312 of this title (relating to Sludge Use, Disposal, and Transportation).
   3. (3) Scum from a clarifier in a facility not using an activated sludge process and an aerated lagoon must be discharged to a sludge digester or may use another disposal method that complies with Chapter 312 of this title.
   4. (4) Discharge of scum to an open drying area is prohibited.
   5. (5) A system with a design flow equal to or greater than 10,000 gallons per day (gpd) must use a mechanical skimmer.
   6. (6) A system with a design flow less than 10,000 gpd may use hydraulic differential skimming if the scum pickup is capable of removing scum from the entire operating surface.
   7. (7) A scum pump must be specifically designed to pump scum.

3. (c) Effluent weirs.

   1. (1) An effluent weir must prevent turbulence or a localized high vertical flow velocity in a clarifier.
   2. (2) A weir must be located a minimum of 6.0 inches from an outer wall or baffle and must prevent the short-circuiting of flow through a clarifier.
   3. (3) A weir must be adjustable to allow leveling of the weir and to provide for minor changes to the water surface elevation in a clarifier.
   4. (4) For a facility with a design flow of less than 1.0 million gallons per day (mgd), the weir loading must not exceed 20,000 gpd at the peak flow per linear foot of weir length.
   5. (5) For a facility with a design flow equal to or greater than 1.0 mgd, the weir loading must not exceed 30,000 gpd at the peak flow per linear foot of weir length.
   6. (6) A center-feed circular clarifier must have overflow weirs around the entire perimeter of the clarifier.

4. (d) Sludge Pipes.

   1. (1) Sludge transfer from a clarifier to a subsequent processing unit must not negatively affect treatment efficiency.
   2. (2) A sludge pipe must be a minimum of 4.0 inches in diameter.
   3. (3) The flow velocity in a sludge pipe must be greater than 2.0 feet per second.
   4. (4) Each sludge pipe must have a means to remove any blockage.
5. (e) Sludge Collection Equipment. A clarifier must include mechanical sludge collecting equipment if it is part of a wastewater treatment facility with a design flow of 10,000 gpd or greater.

6. (f) Pumped Inflow.

   1. (1) For a facility with pumped inflow, a clarifier must be able to accommodate all anticipated flow without overflow.
   2. (2) A facility must hydraulically accommodate peak flows without adversely affecting the treatment processes.

7. (g) Side Water Depth (SWD).

   1. (1) The SWD is defined as:

      1. (A) the water depth from the top of the cone in a cone bottom tank to the water surface; or
      2. (B) the water depth from 2.0 feet above the bottom of a flat bottom tank with a hydraulic sludge removal mechanism.

   2. (2) A clarifier with a mechanical sludge collector and a surface area:

      1. (A) equal to or greater than 300 square feet (sf) must have a minimum SWD of 10.0 feet.
      2. (B) less than 300 sf must have a minimum SWD of 8.0 feet.
   3. (3) A clarifier with a hopper bottom must determine the SWD using the following equation:
      Attached Graphic
      
   4. (4) An SWD computed using Equation F.1 in paragraph (3) of this subsection excludes the hopper portion of a clarifier. The upper third of the hopper portion of a hopper bottom clarifier may be counted as part of the SWD only if the surface area of the hopper bottom clarifier is increased by 15% over the surface area determined from the design surface loading calculated using Figure: 30 TAC §217.154(c)(1), Table F.2 of this title (relating to Aeration Basin and Clarifier Sizing--Traditional Design), and if an activated sludge facility includes a flow equalization basin. The SWD of a hopper bottom clarifier must never be less than 5.0 feet.

8. (h) Restrictions on Hopper Bottom Clarifiers.

   1. (1) A hopper bottom clarifier without mechanical sludge collection equipment is prohibited for use in a facility with a maximum flow equal to or greater than 10,000 gpd.
   2. (2) Each hopper cell of a hopper bottom clarifier must have individually controlled sludge removal equipment.
   3. (3) A hopper bottom clarifier must have a smooth wall finish.
   4. (4) A hopper bottom clarifier must have an upper hopper slope of not less than 60 degrees from horizontal.
9. (i) Restrictions on Short Circuiting. The influent stilling baffle and effluent weir must prevent short circuiting.

10. (j) Return Sludge Pumping Capacity.

    1. (1) The capacity of a return sludge-pumping unit must be calculated based on the area of an activated sludge clarifier(s), including the stilling well area.
    2. (2) The return sludge pumping capacity is the clarifier underflow rate in gallons per day per square foot (gpd/sf).
    3. (3) A return sludge pumping system must be capable of pumping least 200 gpd/sf but not more than 400 gpd/sf.
    4. (4) The pumping capacity may be controlled via throttling, variable speed drives, or multiple pump operation.

Source Note:The provisions of this §217.152 adopted to be effective August 28, 2008, 33 TexReg 6843.