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Mercury
Work Group
Phase I Reports >> Infrastructure Report
Executive Summary | End-of-Pipe Report |
Operations Report | Infrastructure Report
For more information,
contact David Eppstein by email at
deppstein@masco.harvard.edu,
or by calling 617-632-2860.
1.0 PROBLEM OVERVIEW
Mercury is a prohibited substance within the Massachusetts Water
Resources Authority (MWRA) district, with an enforceable wastewater
discharge limit, at the present time, of one (1) part per billion
(ppb). The MWRA has issued Notices of Violation (NOV) for first
time mercury discharge results above one (1) ppb and Notices of
Noncompliance (NON) to all sewer users with repeat mercury discharge
violations. NOVs and NONs were issued to a number of hospitals
and institutions during the time period of 1993 - 1995. A number
of these institutions joined in a collaborative effort with the
Medical, Academic and Scientific Community Organization (MASCO)
and the MWRA to identify the sources and methods of removing the
contaminate from the wastewater effluent. The MWRA/MASCO Hospital
Mercury Work Group was divided into three subcommittees: Operations,
Infrastructure and End-of-Pipe.
The Infrastructure Subcommittee focused on developing a "Special
Waste" conveyance plumbing maintenance Guidebook intended
to help those institutions experiencing problems with mercury
contaminated biomass within their systems. Research from several
institutions provided information indicating that the organic
materials entering these systems act as a food source for biological
growth. This "biomass" was found to readily absorb
or accumulate mercury within these "Special Waste" plumbing
systems. Beth Israel Hospital, for example, determined that the
biomass inside their conveyance system contained as much as 1,000
parts per million (ppm) of mercury. As bits of these biosolids
would periodically break off and be flushed out of the systems,
they would carry the concentrated mercury with them. This would
result in a display of elevated concentrations of mercury, once
the solids were digested and the sample analyzed. Some of the
maintenance procedures that are discussed in this Guidebook for
the control or elimination of biomass growth are: trap cleaning,
powerwashing, chemical cleaning and associated procedures.
As previously explained, mercury accumulation within "Special
Waste" conveyance piping systems containing biomass growth
with mercury creates a complicated wastewater compliance issue.
But, through institutional efforts, two techniques, trap cleaning
and conveyance pipe powerwashing, have been identified, tested
and proven to be very successful with biomass removal and mercury
sources identification.
The trap cleaning procedures simply require that a trap be removed,
the contents be collected for off-site disposal, and the trap
cleaned with a rag or brush prior to being placed back into operation.
The powerwashing procedure provides a physical scouring effect
on the accumulated biomass adhered to plumbing and piping infrastructure.
Powerwashing is an effective, but not permanent, method for removing
biomass and preventing biosolids from appearing in the effluent
discharges. Powerwashing techniques are most efficient when performed
on glass piping. With thermoplastic piping, some technique modification
is required. Powerwashing activities usually require a minimum
of two people: One serving as the powerwash operator; and the
other as an observer of the nozzle and hose as it moves through
the conveyance piping.
Since trap cleaning and conveyance pipe powerwashing will not
permanently remove biomass, periodic cleanings will be necessary
to help ensure recurring growth is removed. In an effort to augment
or perhaps even eliminate the need for trap cleaning and powerwashing
activities, several means of chemical cleaning were also tested
and evaluated. Some of the chemicals succeeded in softening or
loosening the biomass, and others actually facilitated the removal
of bulky segments of biomass. But not one of the methods tested
was capable of completely removing biomass from the piping systems.
In addition, some of the chemicals had significant health and
safety issues associated with them, making their use in the field
impractical. Consequently, not one of the chemical cleaning means
tested is recommended for use.
The Infrastructure Subcommittee also found that neutralization
sumps or tanks (chip tanks) that are often used for the pretreatment
of wastewaters containing dilute acids and alkalis from laboratory
sinks cannot be used in facilities discharging significant quantities
of organic materials due to the fact that the biomass present
will coat the marble chips, rendering the media useless. It is,
therefore, recommended that institutions review the efficacy of
these systems, and replace them with active (adjustable) neutralization
systems when and where appropriate.
Adjustment tanks for pH can be used to treat all "Special
Wastes" including dilute acids and alkalis, and wastewater
containing organic materials. The anticipated flows through the
waste piping system may dictate the use of a two tank system;
the first tank being a mix tank for rough neutralizing and a trim
tank for final adjustment prior to discharge to the sewer system.
As required by the Massachusetts State Plumbing Code, 248 CMR
2.13 (12/1/93), all plans and specifications for "Special
Waste" piping and pretreatment systems shall be prepared
by a Registered Professional Engineer and shall be submitted to
the local Plumbing Inspector for approval prior to installation.
Systems adjusting pH are to be accessible for maintenance, repair,
operation, and sampling procedures. The operation and maintenance
requirements of these pH adjustment systems are detailed in 314
CMR 12.00, Division of Water Pollution Control regulations. In
addition, these wastewater pretreatment systems are required to
be operated by certified operators. Certification requirements
for wastewater pretreatment system operators are detailed in 257
CMR 2.00, Board of Certification of Wastewater Treatment Facilities
regulations.
The installation of flow monitoring devices at several facilities
(carried out as part of the Infrastructure Subcommittee's analysis
of wastewater characteristics) also provided documentation of
the tendency to over estimate institutional flow rates. Since
the MWRA bases permitting and sampling fees, in part, on flow,
additional sampling and permitting fees may be avoided if actual
flow rates are obtained via the installation of flow monitoring
devices. In most cases, these devices can pay for themselves
in a short period of time from savings derived from reduced sampling
and reporting requirements.
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