1. (a) Horizontal Flow Grit Chambers.

   1. (1) Velocity through a grit chamber must range at least 0.8 feet per second but not more than 1.3 feet per second.
   2. (2) A grit chamber channel must minimize turbulence and provide uniform velocity across the channel.
   3. (3) The channel size must accommodate the grit removal equipment capacity and grit storage.

2. (b) Aerated Grit Chambers.

   1. (1) An air diffuser and baffle arrangement design must separate the size of grit planned for removal.
   2. (2) The aeration equipment must vary air feed rates along the length of a grit chamber from 3.0 seconds per cubic foot per meter (scfm) per linear foot but not more than 8.0 scfm per linear foot.
   3. (3) A grit chamber must have a hydraulic detention time of at least 3.0 minutes.
   4. (4) A grit chamber must include a grit hopper located under an air diffuser.

3. (c) Mechanical Grit Chambers.

   1. (1) The velocity through mechanical grit chambers must be no greater than 1.0 foot per second at the design flow.
   2. (2) A channel must include a grit hopper at the side of a tank contiguous to a grit removal mechanism.
   3. (3) An inlet must include baffles to prevent short-circuiting.

   4. (4) Grit removal must be provided by one of the following:

      1. (A) Reciprocating rake;
      2. (B) Screw conveyor; or
      3. (C) Air lift pump.

4. (d) Cyclonic Degritters.

   1. (1) A cyclonic degritter must prevent entry-to-overflow short circuit.
   2. (2) A cyclonic degritter must include an adjustable apex with a quick disconnect assembly to remove any oversized object.
   3. (3) Detention time in a cyclonic degritter must be at least 1.0 minute at the design flow.
   4. (4) The flow velocity must be at least 1.0 foot per second but not more than 2.0 feet per second at the design flow.
   5. (5) A screening unit must be installed upstream of a cyclonic degritter.

5. (e) Vortex Grit Chamber.

   1. (1) An inlet channel must include a straight length in order to deliver smooth flow into the vortex grit chamber.
   2. (2) Minimum initial inlet velocity at the peak flow must be at least 2.0 feet per second.
   3. (3) A vortex system must include rotating paddles in the center of a grit chamber and must rotate at a maximum 21 revolutions per minute.
   4. (4) An outlet channel must maintain a constant elevation.
   5. (5) Grit removal from a grit storage chamber must be by pumps specifically designed to handle grit.

Source Note:The provisions of this §217.125 adopted to be effective August 28, 2008, 33 TexReg 6843.