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Mercury
Work Group
Phase II Reports >> Pretreatment Manual
Facilities Loadings
| Pretreatment Manual |
Tech. Identification
Hg Management Guidebook | Mercury Products
Database
For more
information, contact David Eppstein by email at
deppstein@masco.harvard.edu,
or by calling 617-632-2860.
2.0 BACKGROUND INFORMATION ON PRETREATMENT
In
areas served by municipal sewers, pretreatment of industrial
wastewater discharges is often required to limit the discharge
of toxic, corrosive, or other pollutants into the sewer system
and associated sewage treatment facilities. Sewage treatment
facilities that are owned by states and municipalities are known
as Publicly Owned Treatment Works (POTW). For purposes of this
Manual, pretreatment means the reduction of the amount of
pollutants, the elimination of pollutants, or the alteration of
the nature of pollutant properties in wastewater prior to or in
lieu of discharging or otherwise introducing such pollutants
into a POTW. The reduction or alteration may be obtained by
physical, chemical, or biological processes, process changes or
by other means, except not by dilution.
In most
districts, both general and specific discharge limits are
applied to all industrial users of the POTW system. In general,
industrial wastewater sewer discharges must be controlled to
prevent:
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Harm
or interference with the sewer system or any POTW treatment
process, including sludge use, management, or disposal.
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Passage
(pass-through) of untreated pollutants through the POTW that
could cause a violation of any federal or state law or
permit.
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Any
violation of water quality criteria from the POTW effluent
or adverse effects on the receiving waters.
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Threat
of endangerment of the life, health, or welfare of any
person or persons (including sewer and POTW workers) or of
the public health, safety, or welfare, or the environment,
or public property (including fire or explosion hazards in
sewers or the POTW).
As part
of the EPA National Pollution Discharge Elimination System (NPDES)
permit system, the operator of a POTW is periodically required
to evaluate the specific discharge limits it sets for industrial
wastewater relative to existing federal and state environmental
quality criteria. These specific industrial discharge limits are
called Local Limits. To conform with federal and state
guidelines, an evaluation of Local Limits must be based upon a
substantial body of analytical data including the quantity and
quality of industrial sewer discharges, non-industrial sewer
discharges, treatment plant pollutant removal rates, and
residual biosolids (sludge).
In the
Boston Metropolitan Sewerage Service Area, the MWRA found in its
Local Limits evaluations that specific industrial discharge
limits were required for several heavy metals and organic
compounds and, furthermore, that prohibitions were required for
industrial discharges of pesticides, polychorinated biphenyls,
phenanthrene, and mercury. The applicable Local Limits and
discharge prohibitions are included in the MWRA Sewer Use
Regulations (360 CMR 10.000) and appear as requirements in all
MWRA sewer use permits issued to industrial dischargers.
For
mercury, the MWRA developed an enforcement limit for the
prohibition that requires that samples of an industrial
discharge show a maximum mercury concentration of 1.0 micrograms
per liter (µg/L)1. The basis for this enforcement
limit is a statistical evaluation that determined that mercury
would be present if detected in a wastewater sample at a
concentration greater than 1.0 µg/L (i.e., five times
the typical analytical laboratory detection limit of 0.2 µg/L).
Thus, adoption of the enforcement limit eliminates the
possibility of a false positive analytical result for which the
MWRA would take a noncompliance enforcement action.
To
comply with the MWRA Local Limits, each permitted industrial
facility should study its proposed or existing wastewater
discharges to find the most economical and practical approaches
to meet the Limits. For some facilities, compliance with all
Local Limits may be achieved by implementation of a source
reduction program. For other facilities, source reduction
combined with pretreatment, or pretreatment alone, may be
required. Often, the lowest capital and operating costs for a
new pretreatment system are achieved when the system at each
discharge point is integrated with source reduction, source
segregation, and other aspects of facilities management.
1The
concentration unit of (µg/L) is often referred to as
"parts per billion" (ppb).
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