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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
In a limestone contactor, water flows through a bed of crushed
sieved limestone in a similar way as it would flow through a sand
filter (Spencer, 2000). The pH of water that flows through the
limestone bed will be adjusted until it nears equilibrium with
calcium carbonate (CaCO3(s)). The components
of a contactor include a contact tank, limestone bed, inlet line,
outlet line, overflow line, access lid (for closed system contactor
only) and a flush outlet line (DeSouza et al., 2000).
There are two types of contactors: (i) open and (ii) closed
system contactor. The former is exposed to the atmosphere and
the latter is covered from the atmosphere. There are also contactors
that are built in pressurized vessels (Stauder, 2002).
Limestone contactors are typically located at the end of the
treatment train – after filtration, primary disinfection
and chlorine contact (Spencer, 2000 and Benjamin et al., 1992).
According to Spencer (2000) and Benjamin et al. (1992), by placing
a contactor this way ensures the pH is maintained at a low level
for effective chlorination. However, there are also contactors
that are located after filtration and before chlorine addition
(Stauder, 2002). Most of these contactors are located in Germany.
The reason for placing the contactor before chlorine addition
is because disinfection is not required in most limestone contactor
plants in Germany especially if the plants are treating high quality
deep spring water with very low turbidity (less than 0.1 NTU)
and no or very low number of coliforms (Stauder, 2003).
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