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For more
information, contact David Eppstein by email at
deppstein@masco.harvard.edu,
or by calling 617-632-2860.
10.0 PRETREATMENT SYSTEM PILOT TESTING
The
results of bench-scale testing of different pretreatment systems
can provide a good starting point for an onsite pilot testing
program. In fact, it is better to start pilot testing when there
is some understanding about the pretreatment unit operations
that are likely to be needed for the proposed feasible
pretreatment systems. Each pretreatment system might require
different unit operations that might include equalization,
pre-filtering, softening, pH adjustment, chemical additions, and
removal of interfering matrices or contaminants by, for example,
sterilization or adsorption.
The
purpose of pilot testing is to find out how best to design and
operate each element of the future full-scale pretreatment
system and not only to determine possible effluent quality. The
issue of possible system performance should have been addressed
during a wastewater characterization effort and bench-scale
feasibility and treatability testing. In addition to
determinations of design parameters, the pilot testing of
complete, but small-scale, pretreatment systems can also help
identify any problems that may occur during long-term operations
of the full-scale systems. Possible operating problems that
could occur during pilot testing include reductions in
performance from media fouling or from contaminant buildup.
During testing, therefore, it may be necessary to make and test
modifications or additions to the pilot system.
Therefore,
pilot pretreatment systems should run for extended periods, i.e.,
for several weeks or months, so that the full range of actual
facility wastewater can be experienced and comparative
information can be developed. For each tested system, all
equipment should go through all operating cycles at least once
and preferably several times. These cycles would include, for
example, membrane cleaning, filter backwashes, or resin column
and activated carbon regenerations. After each of these cycles,
measurements should be taken to learn if there has been any
decrease in normal operating performance. The measurements would
help determine the long-term suitability and life cycle costs of
each unit operation of the proposed systems.
If the
pilot system is a batch type, processing one batch of wastewater
at a time, it is often convenient to operate the batch system
once per day. For a complete test, however, the system should be
run on wastewater produced at different times and on different
shifts. A batch-type pilot system should not be considered if a
continuous full-scale pretreatment system is anticipated. For
continuous pilot systems, a qualified operator should be
available throughout all periods of operations.
Pilot
pretreatment systems should be run on all anticipated waste
streams, including all minor waste streams and periodic backwash
and blowdown streams, floor cleaning wastewater, and other
infrequent minor flows from likely maintenance operations. These
streams can contain compounds that could upset a pretreatment
system. Also, possible daily, weekly, and seasonal fluctuations
in the waste stream composition should be considered.
The
effects of all operational variables should be investigated and
understood (flow, pressure differential, current density,
recycle rate, pH, oxidation/reduction potential (ORP), feed
concentration, etc.). After pilot system optimization, scale up
information should be developed and operational ranges should be
established (chemical dosages, settling rates, sludge generation
volumes and densities, reaction times, floc characteristics,
etc.). These operational factors should be determined routinely
for the duration of the testing. Often, they are expressed on a
normalized basis, i.e., per square foot, cubic foot, psi,
ampere, or other system size or driving force parameter.
Effluent quality should also be verified under various operating
conditions.
All
residuals generated by each unit operation of the pilot system
should be carefully considered and the ultimate fates and
disposal methods should be determined. At the same time that
effluent quality is tested, analytical tests of the residuals
should be performed for the contaminants of concern. In
addition, hazardous material determinations (corrosivity,
reactivity, toxicity, and the EPA Toxicity Characteristic
Leaching Procedure (TCLP)) should be performed. Residual
handling operations (such as evaporators, filter presses, sludge
thickeners, centrifuges, etc.) should be bench-scale tested or,
preferably, pilot tested. Mass balances on key parameters should
be done to obtain a full understanding of the fate of pollutants
(i.e., is the pollutant of concern destroyed, is it
transferred into the sludge, is it volatilized, or is it
accumulating and will it eventually foul the system?).
Energy
consumption should be investigated to gauge any extra costs of
the system. Inductive (motors) and resistive (heating)
electrical energy requirements should be estimated for the full
scale system. These considerations especially apply to high
pressure unit operations such as reverse osmosis and to high
temperature unit operations such as evaporation. The
requirements for other utilities (e.g., steam, gas,
water, compressed air, and space heating and ventilation) should
be identified as to quantity and quality. Floor space and
headroom requirements for the full scale system should also be
estimated. Noise and odor concerns should be explored.
Accessibility requirements for the equipment should be defined.
Facility
personnel who will be working with the full scale pretreatment
system should be trained to operate the pilot equipment.
Requirements for operators as to required skill level and
training, including necessary licenses, should be determined.
Training should include the theory behind the wastewater
pretreatment process and contaminant removal and the mechanics
of the equipment and controls. The training issue should be
addressed early so the operations personnel will have completed
training and be certified by the time the full scale treatment
system equipment is in place. In addition, this type of employee
involvement generates a sense of pride, security, and ownership,
which is helpful during any planned changes in daily routines
and operational procedures.
At some
point in this process, full scale system capital and operating
costs can be fairly closely estimated. An economic analysis
could be done to compare competing pretreatment technologies. If
only one pretreatment system is pilot tested, the results of the
economic analysis could still be used to familiarize the
facility management of the scope of the project and to compare
the pretreatment project with possible alternatives.
It
should be understood that a complete bench-scale and pilot
testing program may not be needed if a wastewater stream
consists of easily treated wastes. For example, some wastewater
streams may contain no buffering agents and may require only pH
adjustment (neutralization) to meet discharge regulations. A
good source of information may be similar facilities and types
of businesses that already have pretreatment systems. During
initial planning stages, first-hand recommendations,
endorsements, and criticisms for both engineering firms and
vendors may be invaluable. Remember, however, that no two
wastewater streams will be exactly alike, and pretreatment
requirements may differ.
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