Iron and Manganese Removal - Public Water Systems - page 448

TABLE 14-1. ( Continued )

Raw Water Metal
Concentration
Applicabale for
Treatment

Typical Hydraulic
Filter Loading
Rate

Factors Affecting
Removal of Iron and
Manganese

Detention Time
Prior to Filtration

Notes and
Comments

Operational
Considerations

Backwashing
Requirements Treatment Option Filtration Type Permitting

Chlorine dioxide
and filtration

Fe: Unlimited
Mn: Unlimited if
sufficient time is
provided to com-
plete the reaction

Pressure or
gravity
filters with
either:
1. Dual media
of anthra-
cite and
sand
2. Dual media
of anthra-
cite and
greensand
or oxide-
coated me-
dium

With silica sand:
1. Gravity, 2-5
gpm / ft 2 (4.9-
12.2 m / h)
2. Pressure 4-5
gpm / ft 2 (9.8-
12.2 m / h)
With greensand:

Fe reaction is very
fast. Mn reac-
tion at neutral
pH requires

Rate of removal and
treatment perform-
ance are improved
with:

Requires on-site
generation and
two chemical
feeds. ClO 2 is
more commonly
used for
disinfection.

Requires on-site gen-
eration and the
handling of two
chemicals. Opera-
tionally complex.

Anticipated filter
run times of
24 to 48 hr
and backwash
rates of 12-
16 gpm / ft 2
(29-39 m / h)
are typical
with back-
wash volumes
of2to5%of
the water pro-
duced

Readily accepted
by the regula-
tory agencies

6hr. • Increasing

temperature

• Higher pH

• Decreasing TOC

content
Oxidation and re-
moval of Mn are
difficult at neutral
pH without a long
detention time.

4 gpm / ft 2 (9.8
m / h) max.

Oxide-coated or
catalytic media

Fe: Unlimited;
TOC

Pressure or
gravity fil-
ters with
one of the
following:
1. MnO 2 ore
2. Greensand
media
3. Manganese
dioxide
coated
silicon
dioxide
4. Conven-
tional silica
sand media
conditioned
with
KMnO 4

2-10 gpm / ft 2
(4.9-12.2 m / h)
depending on
the metal con-
centration. For
Mn ore,
5-15 gpm / ft 2
(12.2-36.7
m / h).

Metals adsorbed
onto the media
and held there
until backwash-
ing. No deten-
tion time
required for re-
moval. Media
require regular
or continuous
regeneration to
maintain
effectiveness.

Generally not recom-
mended for water
with TOC

Often used with a
continuous Cl 2
or KMnO 4 feed
for regeneration
of the media.
The Cl 2 and
KMnO 4 will
also oxidize the
iron and reduce
the loading on
the media.

Simple to use and
control. Because of
the sensitivity of
the media to TOC
concentration, raw
water quality as-
sessment is essen-
tial for success of
the process. Chem-
ical requirements
are reduced be-
cause of media
adsorption.

Filter run times:
•

Readily accepted
by the regula-
tory agencies

2 mg/L
Mn:Unlimited;
TOC

Standard me-
dia: 24-48 hr 1mg/

L because fouling
of the media may
result. Media re-
quire regular or
continuous regener-
ation with Cl 2 or
KMnO 4 to work
effectively.

2 mg/L • Greensand:

24 hr

• MnO 2 :

8-12 hr
Backwash rates:
•

Standard
media:
15 gpm / ft 2
(37 m / h)

• Greensand: 12

gpm / ft 2
(29 m / h)

• MnO 2 ore:

25-30 gpm / ft 2
(61-73 m / h)