SECTION 252:626-9-8. Clarification

(a)   Standard design.

(1)   Rapid mix. Rapid mix means the rapid dispersion of chemicals throughout the water to be treated. Provide for the following:

(A)   equip mixing basins with mechanical mixing devices capable of adjustment to compensate for variations in raw water quality and flow. Commercial in-line static mixers capable of producing results equal to basins containing mechanical mixers at all anticipated flows will be acceptable,

(B)   the maximum detention time of the rapid mix basin, at design flow is 30 seconds, and

(C)   locate the rapid mix and flocculation basins as close together as possible.

(2)   Flocculation. Flocculation means the agitation of water at low velocities through gentle stirring by hydraulic or mechanical means. Arrange piping to allow either unit to be removed from service without disrupting operation of the treatment plant.

(A)   Flow-through velocity must be 0.5 to 1.5 ft/min, with a detention time for floc formation of at least 30 minutes.

(B)   Provide variable speed drives to control the speed of agitators to a peripheral paddle speed of 0.5 to 3.0 ft/s.

(C)   Locate flocculation and sedimentation basins as close together as possible. The velocity of flocculated water through pipes or conduits to settling basins must be 0.5 to 1.5 ft/s. Design to minimize turbulence at bends and changes in direction.

(D)   Provide a basin drain line of at least four inches (4") in diameter.

(E)   Baffling may be used to provide for flocculation. The design shall be such that the velocities and flows in this paragraph will be maintained.

(3)   Sedimentation. Conventional horizontal flow sedimentation basins shall conform to the following.

(A)   Sedimentation must follow flocculation. Arrange piping to allow either unit to be removed from service without disrupting operation of the treatment plant.

(B)   The following criteria apply to conventional sedimentation units:

(i)   a minimum detention time of 4 hours is required except when used for lime-soda softening of ground water, the settling time is reduced to a minimum of 2 hours,

(ii)   design basins to prevent short-circuiting. Design inlets to distribute water equally and at uniform velocities. Open ports, submerged ports, or similar entrance arrangements are required. Design port to provide uniform flows across the basin and control headloss to prevent floc breakage,

(iii)   provide outlet weirs and maintain velocities suitable for settling in the basin,

(iv)   limit flow rate over the weir to 20,000 gal/day/ft of weir length,

(v)   limit the velocity through the basin to 0.5 ft/min,

(vi)   design basins with mechanical residuals removal and slope the floor to conform to manufacturer's recommendations. Provide a basin drain line of at least 4 inches in diameter,

(vii)   rectangular basins must have a minimum length-to-width ratio of 2:1, and

(viii)   make provisions for the operator to observe or sample residuals being withdrawn from the unit.

(C)   Tube settlers.

(i)   Set tubes at a 60-degree angle to the flow.

(ii)   A minimum detention time of three (3) hours is required for surface water treatment and two (2) hours for groundwater treatment.

(iii)   Design tube settlers to maintain velocities suitable for settling in the basin and to minimize short-circuiting.

(iv)   Size drain piping to facilitate a quick flush of the settler units and to prevent flooding other portions of the plant.

(v)   Provide sufficient freeboard above the top of settlers to prevent freezing in the units in outdoor installations

(vi)   The maximum application rate is 2 gpm per square foot of cross-sectional area.

(vii)   Provide flushing lines, equipped with backflow prevention, to facilitate maintenance and cleaning.

(b)   Solids contact unit.

(1)   Installation of equipment. Supervision of all mechanical equipment installation by a representative of the manufacturer at the time of installation and initial operation is required.

(2)   Sampling taps. Adequate piping with sampling taps located to permit the collection of samples from critical portions of the units are required.

(3)   Chemical feed. Apply chemicals at points and means necessary to ensure satisfactory mixing with the water.

(4)   Mixing. Rapid mix units ahead of the solids contact units, must comply with OAC 252:626-9-8 (a)(1). Construct solids contact mixing devices to provide good mixing of raw water with previously formed residuals particles, and prevent deposition of solids in the mixing zone.

(5)   Flocculation. Flocculation equipment must:

(A)   be adjustable (speed or paddle pitch),

(B)   provide for coagulation in a separate chamber or baffled zone within the unit, and

(C)   provide a combined flocculation and mixing period of not less than 30 minutes.

(6)   Residuals concentrators. Provide either internal or external concentrators to obtain concentrated residuals with a minimum of wastewater.

(7)   Residuals removal. Provide units with suitable controls for residuals withdrawal and the following:

(A)   residuals pipes not less than 4 inches in diameter and equipped with appropriate cleanouts to facilitate cleaning,

(B)   entrance to residuals withdrawal piping that will prevent clogging,

(C)   valves located outside the tank for accessibility, and

(D)   the ability for the operator to observe and sample residuals being withdrawn from the unit.

(8)   Settling zone detention period. Minimum detention times for the settling zone (excluding the zones for mixing, flocculation, and sludge collection) are:

(A)   three hours for suspended solids contact clarifiers and for softeners treating surface water, and

(B)   one and one-half hours for suspended solids contact softeners treating only groundwater.

(9)   Suspended slurry concentrate. Design softening units so that continuous slurry concentrates of 1% or more, by weight, can be maintained.

(10)   Weirs or orifices. Design overflow weirs so that water at the surface of the unit does not travel more than 10 feet horizontally to the collection trough.

(A)   Weirs must be adjustable, and at least equivalent in length to the perimeter of the tank.

(B)   Do not exceed weir loading rates of:

(i)   14,400 gal/day/ft of weir length for units used as clarifiers, and

(ii)   28,800 gal/day/ft of weir length for units used as softeners treating only groundwater.

(C)   Weirs must provide uniform rise rates over the entire area of the tank.

(D)   Where orifices are used, the loading rates per foot of launder rates shall be equivalent to the weir loading rates.

(11)   Upflow rates. Do not exceed upflow rates of:

(A)   1.0 gal/min/ft of area at the residuals separation line for units used as clarifiers, and

(B)   1.75 gal/min/ft of area at the slurry separation line, for units used as softeners treating only groundwater.

[Source: Added at 18 Ok Reg 1612, eff 6-1-01; Amended at 25 Ok Reg 2304, eff 7-11-08; Amended at 29 Ok Reg 1035, eff 7-1-12]