Civil Engineering Reference
In-Depth Information
Ozone reacts to oxidize ferrous iron as shown in Table 14-3. The reaction between
ozone and iron occurs essentially instantaneously and requires no detention time. It
takes place over the wide pH range of 4 to 10, with an optimum of 7.0. Organically
complexed iron may be oxidized by ozone; however, oxidation of this form of iron
should be pilot tested to verify the oxidation process.
Table 14-3 also shows the reaction via which manganese is oxidized by ozone.
Manganese oxidation rates using ozone are acceptable above pH 5.
7
The reaction with
manganese is complete in a few minutes, and a detention tank with a 3-5-minutes
residence time is needed in the system. A typical ozone system is illustrated in Figure
14-3.
During ozonation, overdosing is possible as the manganese is driven to perman-
ganate, a soluble form of manganese that passes through the filter. When this occurs,
the utility may receive consumer complaints of pink water. For groundwaters that have
a reasonably stable water quality and for which the dose remains constant, overdosing
should not be a problem. In water having a variable water quality, the operator may
have to adjust the dosage to meet demand, or instrumentation may be required to
control the process.
Ozone will react with TOC in the water and can break down complex organic
molecules into more AOC. This can lead to problems with slime regrowth in the filters
and the distribution system, as well as higher THM formation. Utilities contemplating
the use of ozone should consider these more complex issues in the design and operation
of the system.
The depth of filtration systems to remove AOC is discussed in Chapter 12, ''Fil-
tration.''
Adsorptive or Catalytic Media Filtration
Special filter media are regularly used successfully in the removal of iron and man-
ganese because of their adsorptive or catalytic capacity. Adsorptive media have the
Ozone Dest
ructi
on Unit
Backwash
Waste
Contact
Tank
Contact
Tank
Pressure
Filter
Primary
Disinfection
Cl
2
Cl
2
O
3
Finished Water
to Distribution System
Electricity
Oxygen
2
Filter Loading = 4-5 gpm/ft
Filter Run Lengths = 24- 48 hr
Ozone
Generator
Filter Efficiency = 96%+
Area Required = 140 ft
2
/MG
Well or Water Source
Fig. 14-3.
Ozonation system for iron and manganese removal
