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Mercury
Work Group
Phase I Reports >> End of Pipe 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.
Executive
Summary
Problem Definition:
The Massachusetts Water
Resources Authority (MWRA) regulations prohibit the discharge of
mercury to the sewerage system. The MWRA currently enforces this
regulation at a level of five (5) times the method detection
limit (MDL) of 0.2 parts per billion (ppb) based on US EPA
analytical method 245.1 which presently results in an effective
discharge limitation of 1.0 ppb. Although it appears that the
most practical means of approaching compliance with this
discharge standard is via a rigorous program of source
identification followed by waste minimization/exclusion, a
component of any affected facility's overall compliance strategy
must include consideration of end-of-pipe pretreatment options.
Approach:
In order to gain an
overall perspective of the problem, the End of Pipe Alternatives
Subcommittee needed "real time" data on concentrations
of mercury actually being discharged from its members.
Questionnaires requesting historical data were issued and field
sampling at certain representative locations was completed in an
effort to compile this data. Based on the limited response
received, it generally appeared that a typical institution which
has employed no waste minimization techniques may have discharge
levels of mercury as high as 1,000 ppb in its effluent. Those
facilities which have been able to implement an aggressive
program of source identification and materials segregation or
substitution, employee education and infrastructure cleaning
have discharge levels on the order of 5 to 10 parts per billion
with a significant portion of the membership in the 3 to 5 ppb
range.
Note that the forms of
mercury being discharged (dissolved, ionic, metallic, methyl
mercury) cannot be differentiated since all obtained results are
given as total. This is important to note since the Subcommittee
has also learned that only methyl mercury poses a threat in the
environment as a bioaccumulating substance.
Using this data, the
Subcommittee was to determine what technologies are presently
available for use in removing fairly low levels of mercury
(e.g., a maximum of 1,000 ppb) to absolute minimum levels (less
than 1 ppb). Accordingly, the Subcommittee compiled a listing of
these technologies as follows:
- Simple Filtration
- Reverse Osmosis
- Chemical
Precipitation/Redox Reactions
- Disinfection
- Membrane
Microfiltration
- Ion Exchange
- Adsorption
- Evaporation
The next task of the
Subcommittee was to interview suppliers of these various
technologies to determine whether individual components or even
combinations of available techniques could be used for mercury
removal after simple neutralization. The goal of the interview
process was not just to hear proposed strategies for a system
but, also, to determine where a technology may have already been
applied to mercury removal from a hospital wastestream. Over the
course of the process, the Subcommittee held fifteen (15)
meetings where presentations by engineers, equipment
manufacturers/suppliers and application specialists were heard
and discussed. It became evident from these interviews that not
very much historical case study information was available so the
Subcommittee attempted to solicit information from preliminary
field trials being completed by some of the equipment suppliers
at both Member and Non-Member Institutions.
Findings:
The Subcommittee
learned that not one of the technologies presented so far is
individually or collectively capable of reducing the
concentration of mercury in a facility's discharge to below 1.0
part per billion on a consistent or sustainable basis. Some of
the technologies have demonstrated abilities in removing 99.7%
of the total mercury from the wastestream prior to discharge but
the treated effluent still has a mercury content at the 3 to 5
ppb level. Most of the technologies should be viewed as
polishing systems only and, as a result, initial pretreatment is
required before these advanced techniques can be applied; all of
which requires a significant amount of space and money to be
installed. We have also learned that there are many
characteristics of our particular wastestreams that, if not
controlled, can significantly and adversely impact some of the
technologies that have been investigated. For example, chlorine
bleach, used as a hospital disinfectant, can cause a rapid
deterioration of the membranes used in nanofiltration and
reverse osmosis based systems. Oil and grease can cause an
almost immediate failure of ion exchange media. The organic
material and biological activity present in the raw wastewater
will use activated carbon as a food source, in turn, causing
premature failure of the media.
The smaller systems
which are capable of handling a few hundred gallons per day have
associated capital costs which range from $10,000 to $20,000 on
up. Those systems which are not initially capital intensive do
have much higher annual operating costs. Larger institutions
with higher flows will be faced with a corresponding higher,
though not directly proportional, costs. For example, one
installation treating about 2,000 gallons of wastewater per day
spent only $100,000 to install a system but continues to incur
operating costs at the rate of $150,000 to $200,000 per year for
media replacement alone. The system, however, does not produce
an effluent which meets the stipulated limit of 1.0 ppb on a
continuing basis. We have also seen systems, in place, which are
reported to have cost in excess of $2,000,000 to install and are
required to be maintained by a minimum staff of eight (8)
Massachusetts certified/licensed operators. Though not designed
or operated specifically for mercury removal, this system
provided us with a perspective on the size and complexity of a
facility necessary for handling more than 100,000 gallons per
day of wastewater (which is typical of some of our larger member
facilities). This system occupies approximately 10,000 square
feet of floor space and has an annual operating budget of
$1,000,000.
Conclusions &
Summary:
In summary:
- we have forged a
unique partnership with the MWRA and have, with this
significant assistance, been able to access data not
otherwise obtainable
- we have compiled
data on hospital wastewater characteristics in "real
time"
- we have reviewed all
currently available technologies via vendor interviews
- we have compiled
analytical data produced from field demonstration trials at
member institutions which show significant removal
efficiencies (99.7%) but still produce an effluent
prohibited from being discharged to the MWRA sewerage system
- we have compiled
preliminary cost information for each technology as a
function of volume
- we are arranging for
the completion of additional field demonstration testing of
proposed pilot systems at Member host facilities.
When we started this
process, our Subcommittee believed that it would find a
technology that was readily available, proven and reasonably
priced. We have heard many vendors claim that they have a system
that is able to meet a 1.0 ppb mercury performance standard.
Upon closer investigation, however, we have not been able to
document that any of the available technologies can consistently
meet our stated objective at any cost. We remain willing to
continue to look at new solutions and to work with the suppliers
to install prototype units within our member institutions to
verify claims of performance. We are not, however, optimistic
about achieving the desired results.
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