12 Va. Admin. Code § 5-590-900 - Cation exchange softening
A. The softening design selected shall be
based upon the mineral qualities of the source water and the desired finished
water quality in conjunction with requirements for disposal of sludge or brine
water, cost of the plant, cost of the chemicals, and the plant
location.
B. Iron, manganese, or a
combination of the two, in the oxidized state or unoxidized state, shall not
exceed 0.3 mg/L in the water applied to the cation exchange material.
C. The units shall be of pressure or gravity
type of either an upflow or downflow design, using automatic or manual
regeneration.
D. The design
capacity for hardness removal shall not exceed 20,000
grains/ft3 when the resin is regenerated with 0.3
pounds of salt per kilograin of hardness removed.
E. The depth of the cation exchange material
shall not be less than three feet.
F. The hydraulic loading rate should not
exceed seven gpm/ft2 and the backwash rate should be
six to eight gpm/ft. 2
G. The freeboard shall depend upon the
specific gravity of the media and the direction of the water flow.
H. The bottoms, strainer systems, and support
for the cation exchange material shall conform to criteria provided for rapid
rate gravity filters. See also
12VAC5-590-874.
I. Facilities shall be included for even
distribution of brine over the entire surface of both upflow and downflow
units. Backwash, rinse, and air relief discharge pipes shall be installed in a
manner as to prevent any possibility of backsiphonage.
J. A bypass shall be provided around the
cation exchange units to produce a blended water of desirable hardness. Meters
shall be installed to measure total water delivered to the distribution system
and on each softener unit. An automatic proportioning or regulating device and
shutoff valve should be provided on the bypass line. In some installations, it
may be necessary to treat the bypassed water to obtain acceptable levels of
iron and manganese in the finished water.
K. Waters having turbidity of five NTUs or
more shall not be applied directly to the cation exchange softener. Silica gel
materials should be used for water having a pH above 8.4 and should not be used
when iron is present. When the applied water contains a chlorine residual, the
cation exchange material shall be a type that is not damaged by the chlorine
residual. Phenolic resin shall not be used.
L. Sampling taps shall be provided for the
collection of representative samples for both bacteriological and chemical
analyses. The taps shall be located to provide for sampling of the softener
influent, softener effluent, and the blended water. The sampling taps for the
blended water shall be at least 20 ft downstream from the point of
blending.
M. Brine measuring or
salt-dissolving tanks and wet salt storage facilities shall be covered. The
makeup water inlet shall have a free fall discharge of two pipe diameters but
not less than two inches above the maximum liquid level of the unit or be
protected from backsiphonage. Water for filling the tank should be distributed
over the entire surface by pipes above the maximum brine level in the tank. The
salt shall be supported on graduated layers of gravel under which is a suitable
means of collecting the brine. Wet salt storage basins must be equipped with
manhole or hatchway openings having raised curbs and watertight covers with
overhanging edges similar to those required for finished water reservoirs.
Overflows, where provided, shall be turned down, have a proper free fall
discharge and be protected with noncorrodible screens or self-closing flap
valves.
N. Wet salt storage basins
shall have sufficient capacity to store at least a 30-day operating
supply.
O. Stabilization of the
finished water for corrosion control shall be considered.
P. Suitable disposal must be provided for the
brine waste.
Q. Pipes and contact
materials shall be resistant to the aggressiveness of the salt.
Notes
Statutory Authority: §§ 32.1-12 and 32.1-170 of the Code of Virginia.
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