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Oklahoma Administrative Code (Last Updated: March 11, 2021) |
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TITLE 252. Department of Environmental Quality |
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Chapter 656. Water Pollution Control Facility Construction Standards |
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Subchapter 13. Preliminary Treatment Standards |
SECTION 252:656-13-2. Grit chambers
Latest version.
- (a) Where required. Grit chambers are required at all mechanical sewage treatment plants, ahead of pumps and other equipment that may be damaged by grit.(b) Outside facilities. Protect grit removal facilities located outside from freezing.(c) Chamber design.(1) Rectangular horizontal-flow grit chambers shall be designed to regulate velocity to minimize organic matter deposition. Channels shall be designed for velocities of 0.8 to 1.3 fps, with a total detention time of 20 seconds to one minute.(2) Aerated grit chambers shall be designed for a detention time of two (2) to five (5) minutes. Aerated grit chambers shall be sized in accordance with Appendix A.(d) Grit washing. Provide grit washing devices to further separate organic and inorganic materials in all chambers not equipped with positive velocity control. Include provisions for draining each unit.(e) Grit removal. Provide facilities for hoisting grit to ground level from equipment located in deep pits, provide access by stairways, and provide adequate ventilation and lighting.(f) Grit disposal. Provide for the removal, handling, storage and disposal of grit.(g) Vortex-type grit chambers.(1) The flow into the grit chamber shall be through a straight and smooth channel. The length of the inlet channel must be at least seven (7) times the width or fifteen (15) feet, whichever is greater.(2) Total detention time in the chamber at design flow is thirty (30) seconds.(3) The equipment specifications shall identify the required grit removal rates. Removal rates shall be based on the equipment manufacturer's specifications for downstream processes and meet the following minimum criteria:(i) 95% removal rate for 50-mesh grit.(ii) 85% removal rate for 70-mesh grit.(iii) 65% removal rate for 100-mesh grit.(4) Provide a propeller with a variable speed drive to operate the unit based on the plant flow.(5) Provide air or water scour to loosen compacted grit and facilitate the grit lifting and removal from the chamber.(6) Provide inclined screws, conveyors, chain elevators or pumps, including top mounted self-priming suction lift pumps to lift the grit from the chamber and transfer the grit to the washing and separating facilities. Air lift pumps shall not be used for this purpose.(7) Automatically controlled grit lifting, washing and separating equipment with the ability to manually override.