Iron and manganese control, as used herein, refers solely to
treatment processes designed specifically for this purpose. The treatment
process used will depend upon the character of the source water. The selection
of one or more treatment processes shall meet specific local conditions as
determined by engineering investigations, including chemical analyses of
representative samples of water to be treated, and receive approval of the
Director. It may be necessary to operate a pilot plant in order to gather all
information pertinent to the design. Consideration should be given to adjust
the pH of the raw water to increase the rate of the chemical reactions
involved.
Removal or treatment of iron and manganese are normally by
the following methods:
(1) Removal by
Oxidation, Detention and Filtration.
(a)
Oxidation.
Oxidation may be by aeration, or by chemical oxidation with
chlorine, potassium permanganate, ozone or chlorine dioxide.
(b) Detention.
(i) Reaction time - A minimum detention time
of twenty minutes shall be provided following aeration in order to insure that
the oxidation reactions are as complete as possible. This minimum detention may
be omitted only where a pilot plant study indicates no need for detention. The
detention basin shall be designed as a holding tank with no provisions for
sludge collection but with sufficient baffling to prevent short
circuiting.
(ii) Sedimentation -
Sedimentation basins shall be provided when treating water with high iron
and/or manganese content, or where chemical coagulation is used to reduce the
load on the filters. Provisions for sludge removal shall be made.
(c) Filtration.
(i) General - Minimum criteria relative to
number, rate of filtration, structural details and hydraulics, filter media,
etc., provided for rapid rate gravity filters shall apply to pressure filters
where appropriate, and may be used in this application but cannot be used in
the filtration of surface waters or following lime-soda softening.
(ii) Details of Design for Pressure Filter -
The filters shall be designed to provide for:
(A) Loss of head gauges on the inlet and
outlet pipes of each filter,
(B) An
easily readable meter or flow indicator on each battery of filters,
(C) Filtration and backwashing of each filter
individually with an arrangement of piping as simple as possible to accomplish
these purposes,
(D) The top of the
washwater collectors to be at least twenty-four (24) inches above the surface
of the media,
(E) The underdrain
system to efficiently collect the filtered water and to uniformly distribute
the backwash water at a rate capable of not less than 15 gpm/sf of filter
area,
(F) Backwash flow indicators
and controls that are easily readable while operating the control
valves,
(G) An air release valve on
the highest point of each filter,
(H) An accessible manhole to facilitate
inspections and repairs,
(I) Means
to observe the wastewater and filters during backwashing, and
(J) Construction to prevent
cross-connection.
(2) Removal by the Lime-soda Softening
Process.
For removal by the lime-soda softening process refer to Part
4, Section 4.4, Softening, in the Recommended Standards for Water Works
(commonly known as "Ten State Standards"), 2007 edition as indicated in
R309-535-10. Those
standards are hereby incorporated by reference and compliance with those
standards shall be required for removal by the lime-soda softening
process.
(3) Removal by
Manganese Greensand Filtration.
This process, consisting of the continuous feed of potassium
permanganate to the influent of a manganese greensand filter, is more
applicable to the removal of manganese than the removal of iron.
(a) Provisions shall be made to apply the
permanganate as far ahead of the filter as practical and at a point immediately
before the filter.
(b) An
anthracite media cap of at least six inches shall be provided over manganese
greensand.
(c) The normal
filtration rate is three gpm/sf.
(d) The normal wash rate is 8 to 10
gpm/sf.
(e) Air washing shall be
provided.
(f) Sample taps shall be
provided:
(i) prior to application of
permanganate,
(ii) immediately
ahead of filtration,
(iii) at a
point between the anthracite media and the manganese greensand,
(iv) halfway down the manganese greensand,
and
(v) at the filter
effluent.
(4)
Removal by Ion Exchange.
This process is not acceptable where either the source water
or wash water contains dissolved oxygen.
(5) Sequestration by Polyphosphates.
This process shall not be used when iron, manganese or a
combination thereof exceeds 1.0 milligram per liter. The total phosphate
applied shall not exceed 10 milligrams per liter as PO4.
Where phosphate treatment is used, satisfactory chlorine residuals shall be
maintained in the distribution system and the following required:
(a) feeding equipment shall conform to the
requirements of
R309-525-11(7),
(b) stock phosphate solution shall be kept
covered and disinfected by carrying approximately 10 mg/l free chlorine
residual,
(c) polyphosphates shall
not be applied ahead of iron and manganese removal treatment. If no iron or
manganese removal treatment is provided, the point of application shall be
prior to any aeration, oxidation or disinfection steps, and
(d) phosphate chemicals must comply with
ANSI/NSF Standard 60.
Sampling taps shall be provided for control purposes. Taps
shall be located on each raw water source, and on each treatment unit influent
and effluent.
Waste generated by iron and manganese control treatment shall
be disposed of in accordance with
R309-525-23.
