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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
(B) MATHEMATICAL MODEL OF LIMESTONE DISSOLUTION
As CaCO3 dissolves from the limestone
contactor media, particle size, bed depth, bed porosity, flow
velocity and pressure drop change with time. It is important to
make design choices for these variables since they affect the
dissolution rate and recharge frequency. Letterman and Kothari
(1995) and Haddad (1986) developed models of limestone dissolution
rate that are sensitive to these variables and can be used for
design. Haddad (1986) used 
12 and 13 to model the limestone dissolution process in a contactor
operating at steady state. Using equations 12 and 13, Letterman,
Haddad and Driscoll (1991) developed a steady-state model that
relates the depth of limestone required in the contactor to the
desired effluent water chemistry, influent water chemistry, limestone
particle size and shape, bed porosity, water temperature and superficial
velocity (
14). This model assumes that the rate of dissolution is controlled
by two resistances that act in series: a surface reaction that
controls the release of calcium from the solid and a mass transfer
resistance that controls the rate of calcium transport between
the solid surface and the bulk solution (Letterman and Kothari,
1995). Based on this kinetic model, Letterman and Kothari (1995)
developed a computer program called DESCON. It can be downloaded
from http://web.syr.edu/~rdletter/software.htm.
It is used to facilitate the design of limestone contactors and
will be discussed later in this module.
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