Current through Vol. 41, No. 13, March 15, 2024
Select the softening process based on mineral qualities of
raw water, desired finished water quality, requirements for disposal of
residuals or brine waste, cost of plant, cost of chemicals and plant
location.
(1)
Lime or lime-soda
process.
(A)
Residuals
removal. Provide mechanical residuals removal equipment in the
sedimentation basin.
(B)
Rapid mix. In addition to the rapid mix requirements of OAC
252:626-9-8(a)(1),
the design of a softening plant must allow for the recycling of previously
formed calcium carbonate crystals (lime residuals) to the rapid mix
basin.
(C)
Filtration.
In addition to the requirements for filter design as set forth in OAC
252:626-9-9, equip
filters with a mechanical surface sweep to assist filter backwashing.
(D)
Stabilization. Equipment for
stabilization of water softened by the lime or lime-soda process is
required.
(2)
Cation exchange process.
(A)
Pre-treatment. Pre-treatment is required when the content of iron,
manganese, or a combination of the two, is 1 mg/l or more.
(B)
Design. Automatic
regeneration based on volume of water softened is required unless manual
regeneration can be justified and is approved by the DEQ. Provide a manual
override on all automatic controls.
(C)
Exchange capacity. Do not
exceed the resin manufacturer's recommended design capacity for hardness
removal and regeneration.
(D)
Depth of resin. The depth of the exchange resin must be at least 3
feet.
(E)
Flow rates.
Do not exceed 7 gal/min/ft2 flow rate for softening
of bed area. Provide for backwash flow rate of 6 B 8
gal/min/ft2 of bed area.
(F)
Freeboard. The freeboard
will depend upon the specific gravity of the resin and the direction of water
flow. Washwater collector shall be twenty-four inches (24") above the top of
the resin on downflow units.
(G)
Underdrains and supporting gravel. Design the bottoms, strainer
systems and support for the exchange resin to conform to criteria provided for
rapid rate gravity filters.
(H)
Brine distribution. Provide for even distribution of the brine
over the entire surface of both upflow and downflow units.
(I)
Blending configuration.
Provide piping around softening units to produce blended water of desirable
hardness. Provide an automatic proportioning or regulating device and shut-off
valve on each line. Install totalizing meters on the bypass line and on each
softener unit. Treatment of the water will be required when iron and/or
manganese levels in the blended water exceed the levels for secondary standards
found in 40 CFR, Part 143.
(J)
Additional limitations. Do not apply water with turbidity of 5 NTU
or more directly to the cation exchange softener. Do not use silica gel resins
for waters having a pH above 8.4 or containing less than 6 mg/l of silica. When
the applied water contains a chlorine residual, the cation exchange resin must
be a type that is not damaged by chlorine.
(K)
Sampling taps. Provide
smooth-nose sampling taps for the collection of representative samples. Locate
the taps to provide sampling of the softener influent, effluent, and blended
water. Install sampling taps for the blended water at least 20 feet downstream
from the point of blending.
(L)
Brine and salt storage tanks. Cover brine measuring or salt
dissolving tanks and wet salt storage facilities and construct them of
corrosion-resistant material. The make-up water inlet must have a free fall
discharge of two pipe diameters above the maximum liquid level of the unit or
obtain DEQ approval of other methods of protection from back-siphonage. Support
the salt on graduated layers of gravel with a suitable means of collecting the
brine. Equip wet salt storage basins with manhole or hatchway openings having
raised curbs and watertight covers with overhanging edges similar to those
required for finished water reservoirs. Overflow, where provided, must have a
free fall discharge and terminate at an approved brine waste disposal
facility.
(M)
Salt storage
capacity. Design salt storage large enough to accommodate a 30-day
supply.
(N)
Stabilization. Provide stabilization for corrosion
control.
(O)
Waste
disposal. Provide a DEQ approved disposal plan for brine waste. If
disposal is to an impoundment, then the impoundment must be lined with a
synthetic liner in accordance with the requirements contained in OAC
252:656.
(P)
Construction
material. Pipes and contact materials must be resistant to the
aggressiveness of salt.
(Q)
Housing. Enclose and separate salt storage from other operating
areas.
(3)
New
technology. Other forms of softening not covered in this subchapter
shall be considered for approval under the conditions of OAC
252:626-3-8
until data from a sufficient number of installations demonstrate their ability
to perform satisfactorily.
(4)
Water quality test equipment. Provide test equipment for pH,
alkalinity and total hardness to determine treatment effectiveness.
Added at 18 Ok Reg 1612,
eff 6-1-01; Amended at 25 Ok Reg 2304, eff
7-11-08