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LIST
OF CONTENTS
Introduction
Process Description
Typical
Contactor
Design
Criteria
Photos, Plans & Specs
Treatment
Performance
Operational
Skills
Automation
Potential
Advantages
Limitations
& Concerns
Pilot
Plant Objectives
Costs
References
Contacts & Facilities
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PROCESS DESCRIPTION - CONTINUED
It is similar to Spraystab I but excludes multi-media filtration
and the water flows in the contactor in an upward direction (Mackintosh,
De Souza and De Villiers, 2003b). The raw groundwater is first
aerated and then flows downward through a tube to the base of
the limestone stabilization unit. Sludge and iron flocs (if iron
is present in the water) will be collected at the base of the
unit. Then, the water is collected and uniformly distributed by
a slotted pipe manifold system through the limestone bed in an
upward direction to be stabilized.
(A) CHEMICAL REACTIONS INVOLVED IN LIMESTONE DISSOLUTION
In order to understand the reactions involved in a limestone
contactor, one must understand the basic principles governing
the carbonate system in natural water and its equilibrium with
limestone. Natural water contains carbonate species such as aqueous
or dissolved carbon dioxide (CO2(aq)),
carbonic acid (H2CO3),
bicarbonate (HCO3-)
and carbonate (CO32-)
(Snoeyink and Jenkins, 1980). In a limestone contactor, the concentrations
of the dissolved carbonate species are driven toward chemical
equilibrium with CaCO3 by dissolving limestone.
It is the interaction of these species that controls the pH in
natural water (De Souza et. al., 2000) and can be undersaturated,
in equilibrium or oversaturated with CaCO3
although low pH and alkalinity waters here are undersaturated
with CaCO3.
The degree of CaCO3 saturation of water
is commonly calculated using the Langelier Index (L.I.).
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