Oklahoma Administrative Code › Title 252 - Department of Environmental Quality › Chapter 656 - Water Pollution Control Facility Construction Standards › Subchapter 17 - Clarifier Standards › Section 252:656-17-2 - Clarifier design considerations

Current through Vol. 41, No. 20, July 1, 2024
(a)
Flow distribution.
Effective flow splitting devices and control
				appurtenances (i.e. gates, splitter boxes, etc.) shall be provided to permit
				proper proportioning of flow and solids loading to each unit throughout the
				expected range of flows.
(b)
Primary clarifier design criteria.
Primary clarifiers shall be
				placed downstream of flow distribution devices. Surface settling rates for
				primary tanks shall not exceed 1,000 gal/ft2/day at
				design average flows or 1,500 gal/ft2/day for peak
				hourly flows. Peak hourly flow is based upon a 2-hour sustained peak, as
				defined by
Wastewater Engineering: Treatment, Disposal &
				Reuse
, Metcalf & Eddy, Inc. 4th Edition
				(2003). The primary clarifier must have a minimum side water depth of twelve
				feet (12'). Clarifier sizing shall be calculated for both flow conditions and
				the larger surface area determined shall be used. Primary settling of normal
				domestic sewage can be expected to remove 30 to 35% of the influent BOD.
				However, anticipated BOD removal for sewage containing appreciable quantities
				of industrial wastes (or chemical additions to be used) shall be determined by
				laboratory tests and consideration of the quantity and character of the
				wastes.
(c)
Secondary
				clarifier design criteria.
See Appendix B.
(d)
Inlet structures.
Design
				inlets to prevent short-circuiting, to dissipate velocity and diffuse flow
				equally across the entire cross-section of the settling chamber. Design
				channels to maintain a velocity of at least 1 fps at one-half design flow. When
				scum ports in the inlet diffusion well baffle are provided, the elevation of
				the bottom edge of the ports shall be no lower than 0.10 feet below the
				elevation of the crest of the overflow weirs.
(e)
Weirs.
Overflow weirs shall
				be adjustable and level.
(1)
Location.
Locate overflow weirs to optimize hydraulic retention
				time and minimize short-circuiting.
(2)
Design rates.
Weir loadings
				shall not exceed 10,000 gal/linear foot/day for plants designed for average
				flows of 1.0 mgd or less. Higher weir loadings may be used for plants designed
				for larger average flows, but shall not exceed 15,000 gal/linear foot/day.
				Where the flow is pumped to the clarifier, the weir length shall be based on
				the average pump delivery rates to avoid short-circuiting.
(3)
Weir troughs.
Design weir
				troughs to prevent submergence at maximum design flow, and to maintain a
				velocity of at least 1 fps at one-half design flow.
(4)
Dewatering.
Provide the
				necessary piping and equipment to permit complete dewatering to the floor for
				the bypassing of individual units for maintenance and repair.
(5)
Freeboard.
Walls shall
				extend at least 6 inches above the surrounding ground surface and provide at
				least 12 inches of freeboard. Provide additional freeboard or wind screens for
				larger clarifiers subject to high velocity wind currents that would cause tank
				surface waves and inhibit scum removal.