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Mercury
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Phase II Reports >> Pretreatment Manual
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Hg Management Guidebook | Mercury Products
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For more
information, contact David Eppstein by email at
deppstein@masco.harvard.edu,
or by calling 617-632-2860.
7.0 COORDINATION OF SOURCE REDUCTION, SEGREGATION, AND
PRETREATMENT
Source
reduction, wastestream segregation, and wastewater
characterization as discussed above are practical steps to
pursue before the design and installation of a pretreatment
system. For the greatest benefit, these steps should be part of
a coordinated effort. Figure 3 depicts a conceptual coordinated
source reduction, segregation, and pretreatment plan for the
special case of mercury in wastewater7.
Implementation of such a plan involves some or all of the
following steps:
Continue
source reduction activities, i.e., identify
mercury-containing products and reagents, reduce their usage, or
find non-mercury or low-mercury alternates. In addition,
investigate procedural changes, technology changes, and
recycling and reuse to reduce the amount of mercury discharged.
Determine
which process wastewater streams have non-detectable
concentrations of mercury and separate them from wastewater
streams containing mercury. Separation may involve waste piping
changes, relocation or consolidation of process operations,
and/or manual collection and transfers. The segregated
mercury-free wastewater streams would be routed beyond a mercury
pretreatment system to reduce its size and capital cost.8
Determine
which process wastewater streams have high concentrations of
mercury and segregate them from other mercury-bearing
wastewater streams to reduce the size, capital cost, and
operating cost of a mercury pretreatment system. These high
mercury streams could be disposed of as medical or hazardous
waste. If it is determined that alternate disposal is not
economical, these streams could be collected into a tank for
continuous metering into the other mercury-bearing wastewater
streams. The mercury pretreatment system would be designed
accordingly.
Determine
which mercury-bearing wastewater streams have other pollutants
that could cause interferences with your mercury pretreatment
system. Interferences with specific mercury removal processes
can sometimes occur from chlorine, detergents, solvents, oil and
grease, phosphates, or heavy metals. Replace or reduce the use
of any problem reagent sources or separately collect the
potentially offending wastewater streams for disposal as medical
or hazardous waste.
For the
remaining mercury-bearing wastewater streams that can be
effectively pretreated, implement equalization of (i.e.,
reduce the variations in) the flow rate and pollutant
concentrations before a mercury pretreatment system. Figure 4
depicts a possible configuration of an equalization tank that
can reduce variations in both flow rate and pollutant
concentrations of a wastewater stream.
Take
the equalized wastewater stream into your mercury pretreatment
system. Typically, the pretreatment system would be installed
only after bench-scale feasibility and treatability tests on
samples of actual wastewater and after on-site pilot system
optimization tests. Combine the treated and untreated process
wastewater streams for final neutralization, flow metering,
monitoring, and discharge to the sewer.
FIGURE
3
FIGURE
4
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