| (a) Inlets.
(1) A clarifier must have an inlet valve or gate.
(2) A clarifier inlet must provide uniform flow and
stilling.
(3) A transfer pipe must not trap or entrain air.
(4) Vertical flow velocity through an inlet stilling
well must not exceed 0.15 feet per second at peak flow.
(5) An inlet distribution channel must be designed
to prevent the settling of solids in the channel.
(b) Pumped Inflow.
(1) For a wastewater treatment facility with pumped
inflow, a clarifier must be able to accommodate all flow without overloading
or overtopping the clarifier effluent weir.
(2) A clarifier must hydraulically accommodate peak
flows without adversely affecting treatment in the clarifier or in
subsequent treatment units.
(c) Scum removal.
(1) A clarifier must include scum baffles and a means
for scum collection and disposal.
(A) A clarifier at a wastewater treatment facility
with a design flow equal to or greater than 10,000 gallons per day
must use a mechanical skimmer.
(B) A clarifier at a wastewater treatment facility
with a design flow less than 10,000 gallons per day may use either
mechanical skimming or hydraulic differential skimming. Hydraulic
differential skimming may only be used if the scum pickup is capable
of removing scum from the entire operating surface of the clarifier.
(2) Scum collected from a clarifier in a wastewater
treatment facility using an activated sludge process or an aerated
lagoon must be:
(A) discharged to an aeration basin or digester; or
(B) disposed of using any method that complies with
Chapter 312 of this title (relating to Sludge Use, Disposal, and Transportation).
(3) If scum contains debris or foreign materials that
were not removed by preliminary treatment, debris and foreign materials
must be removed from the scum before the scum is discharged to a digester
or applied to the land. Otherwise, scum containing debris or other
foreign materials must be sent to a landfill or a sludge-only monofill.
(4) Scum collected from a clarifier in a wastewater
treatment facility not using an activated sludge process and not using
an aerated lagoon must be discharged to a sludge digester or must
be disposed of using any disposal method that complies with Chapter
312 of this title.
(5) Discharge of scum to a drying area that is open
to the atmosphere is prohibited.
(6) Storage or holding of scum in a containment vessel
that is open to the atmosphere is prohibited. Scum must be contained
in a vessel that is not open to the atmosphere or must be routed to
a treatment unit in the wastewater treatment facility for further
processing.
(7) A pump used for pumping scum must be specifically
designed to pump scum.
(d) Clarifier Effluent Weirs.
(1) A clarifier effluent weir must prevent turbulence
or localized high vertical flow velocity in a clarifier.
(2) A clarifier effluent weir must be located a minimum
of 6.0 inches from an outer wall or baffle, except for a clarifier
effluent weir and launder that is attached to a wall. A clarifier
effluent weir must prevent the short-circuiting of flow throughout
the clarifier.
(3) A clarifier effluent weir must be level, and must
be adjustable to allow re-leveling of the weir and to provide for
minor changes to the water surface elevation in the clarifier.
(4) For a wastewater treatment facility with a design
flow of less than 1.0 million gallons per day, the clarifier effluent
weir loading must not exceed 20,000 gallons per day at the peak flow
per linear foot of weir length.
(5) For a wastewater treatment facility with a design
flow equal to or greater than 1.0 million gallons per day, the clarifier
effluent weir loading must not exceed 30,000 gallons per day at the
peak flow per linear foot of weir length.
(6) A center-feed circular clarifier must have effluent
weirs around the entire perimeter of the clarifier.
(e) Sludge Pipes.
(1) The transfer of sludge from a clarifier to a treatment
or processing unit must not negatively affect treatment efficiency
of the unit that receives the sludge.
(2) A sludge pipe must be a minimum of 4.0 inches in
diameter.
(3) The flow velocity in a sludge pipe must be greater
than 2.0 feet per second for a wastewater treatment facility with
a design flow greater than 150,000 gallons per day. For a wastewater
treatment facility with a design flow of 150,000 gallons per day or
less, the flow velocity in the sludge pipe must be greater than 0.5
feet per second. The executive director may consider approving lower
velocities in writing for a wastewater treatment facility that uses
a biological nutrient removal process, on a case-by-case basis.
(4) A sludge pipe must be accessible for cleaning.
(5) A means to remove a blockage from all sludge pipes
must be provided at the wastewater treatment facility.
(f) Sludge Collection Equipment.
(1) A clarifier that is part of a wastewater treatment
facility with a design flow of 10,000 gallons per day or greater must
include mechanical sludge collecting equipment.
(2) A clarifier that is part of a wastewater treatment
facility with a design flow of less than 10,000 gallons per day must
include manual equipment designed to move settled sludge to the sludge
collection pipe, unless mechanical sludge collecting equipment is
provided.
(g) Side Water Depth.
(1) For a secondary clarifier, the side water depth
is defined as:
(A) the water depth from the top of the cone in a cone
bottom tank to the water surface; or
(B) the water depth from 2.0 feet above the bottom
of a flat bottom tank to the water surface.
(2) The minimum side water depth for a clarifier with
a mechanical sludge collector is:
(A) 10.0 feet if the surface area is equal to or greater
than 300 square feet; and
(B) 8.0 feet if the surface area is less than 300 square
feet.
(3) A clarifier with a hopper bottom must have a minimum
side water depth of 8.0 feet, not including the hopper and sump. The
corresponding surface area and surface loading relationships in Figure:
30 TAC §217.152(g)(3) must be used.
Attached Graphic
(4) The hopper portion of a hopper bottom clarifier
must have a vertical depth of at least 4.0 feet.
(h) Restrictions on Hopper Bottom Clarifiers.
(1) A hopper bottom clarifier is prohibited for use
in a wastewater treatment facility with a design flow equal to or
greater than 10,000 gallons per day.
(2) Each hopper cell of a hopper bottom clarifier must
have individually controlled sludge removal equipment.
(3) A hopper bottom clarifier must have a smooth wall
finish.
(4) A hopper bottom clarifier must have an upper hopper
slope of not less than 60 degrees from horizontal.
(i) Restrictions on Short Circuiting. The influent
stilling baffle and effluent clarifier weir must prevent hydraulic
short circuiting.
(j) Return Sludge Pumping Capacity.
(1) The capacity of a return sludge pumping system
must be calculated based on the area of the activated sludge clarifier
or clarifiers, including the stilling well area.
(2) The return sludge pumping capacity must be equal
to or greater than the clarifier underflow rate in gallons per day
per square foot (gpd/sf) with the largest pump out of service.
(3) A return sludge pumping system must be capable
of pumping at least 200 gpd/sf but not more than 400 gpd/sf.
(4) The return sludge pumping capacity must be controlled
via throttling, variable speed drives, or multiple pump operation.
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