xvEPA
United States
Environmental Protection
Agency
EPA/540/F-92/002
February 1992
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Emerging Technology Bulletin
Chemical Treatment and Ultrafiltration
Atomic Energy of Canada, Limited
Technology Description: The Atomic Energy of Canada,
Limited (AECL) process uses chemical pretreatment and subse-
quent ultrafiltration to remove trace concentrations of dissolved
metals from wastewater, contaminated groundwater, and leachate.
The process provides both selective removal of metal contami-
nants and a volume-reduced waste stream amenable to further
treatment.
In the process, a relatively high molecular weight polymer, gener-
ally a commercially available polyelectrolyte, is added to the
wastewater to form large, selective metal-polymer complexes at
desired pH and temperature conditions. The solution, containing
enlarged metal-polymer complexes, is then processed through a
cross-flow ultrafiltration membrane system that retains the cons
plexes (retentate or concentrate), while allowing uncomplexed
ions (such as calcium and/or sodium) to pass through the mem-
brane with the filtered water (permeate). The permeate may be
discharged or recycled, depending on the goals set for metal
removal.
The field-scale unit is 5 feet wide by 7 feet long by 6 feet high.
The skid-mounted system consists of (1) a bank of 5-micron
cartridge premiers, (2) a feed conditioning system with chemicals
for pH adjustment and poryelectrolytes, (3) two banks of hollow-
fiber ultrafitters, (4) a backflush system for cleaning the mem-
brane unit, and (5) associated tanks and instrumentation. The
two banks of filters provide a total membrane surface area of 390
square feet and a permeate rate of about 8 gallons per minute.
The wastewater is pH adjusted and fed through the prefilter for
removal of suspended solids. The filtered wastewater is then
routed to conditioning tanks where the metal-polyelectroryte com-
plexation occurs. The conditioned feed is then pumped to the
uttrafilter assembly through a recirculatton loop. This loop in-
cludes the membranes and provides the necessary contact time
and turbulence for separation of the metal-polyelectrolyte com-
plexes and other suspended and colloidal particles. The perme-
ate stream, which can be discharged, may be continuously with-
drawn, while the concentrate stream, containing most of the
hazardous contaminants, is retained in the recirculation loop until
the desired volume reduction is achieved. Rgure 1 presents a
schematic of the process.
Waste Applicability: The process can be used to treat
wastewater contaminated with trace levels of toxic, heavy metals
that arise from a variety of sources. Specific potential applica-
tions include removal of metals such as cadmium, lead, mercury,
Concentrate Permeate
Figure 1. Chemical Pretreatment and Ultrafiltration Process.
Circulation
Pump
Printed on Recycled Paper
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uranium, manganese, nickel, chromium, and silver. Dissolved
metal concentrations amenable to treatment range from a few to
tens of parts per million. In addition to dissolved metals, other
inorganic and organic materials present as suspended or colloi-
dal solids can also be removed. The sole residue generated by
the process is the ultrafiltration concentrate - generally constitut-
ing 5% to 20% of the feed volume.
Test Results: Process testing was accomplished at bench-,
pilot-, and field-scale. It was verified that the method provides
the necessary metal ion size enlargement for ultrafiltration sepa-
ration of metals, and that the permeate stream is essentially free
of toxic metal contamination. In addition to metal-polyelectrolyte
complexation, certain metals can be precipitated by pH adjust-
ment to exploit the combined effects of complexation, precipita-
tion, and free ion adsorption.
Bench-scale testing of the process with two membrane types and
two polyelectrolytes indicated that cadmium, lead, and mercury
can be removed at rates greater than 95%. Although a bit more
susceptible to fouling, polysufone membranes are preferred over
cellulose acetate membranes because of their greater perme-
ation rates and ability to perform under a wide range of pH
conditions.
Pilot-scale testing of the process yielded metal removal rates
consistent with the bench-scale tests. The pilot unit, utilizing
hollow-fiber membranes, operated at pressure differentials of 20 -
25 psig. It was noted that at this scale, a prefiltration step is
critical to the operation of the hollow-fiber units in order to
prevent membrane plugging. Further, the pilot-scale studies
confirmed earlier results showing the need for a polyelectrolyte to
total metal concentration ratrcrbf about 3 to 10.
The field-scale unit provided separation efficiencies in excess of
90% for mercury, cadmium, and lead. It was shown that the
presence of iron and sulfate ions in the feed, however, greatly
influences metal removal efficiencies and can lead to poor re-
sults. The unit performed at less than anticipated efficiency
when processing wastewater in the field, due in part to the
ineffectiveness of the polyelectrolyte chosen, the high ionic
strength of the waste feed, and the interference of large quanti-
ties of iron, calcium, and sulfate ions. Subsequent testing of the
unit has shown that, with proper treatability studies, acceptable
field performance can be obtained.
For Further information:
EPA Project Manager:
John F. Martin
U.S. EPA Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
-(543) 569^758^ETS: 684*7758) -
Technology Developer Contact::
Leo P. Buckley
Atomic Energy of Canada, Limited
Waste Management Systems
Chalk River Laboratories
Chalk River, Ontario KOJ 1JO, Canada
613-584-3311
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/540/F-92/002
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