Bench-Scale Demonstration Of A Peat Bed For Removal Of Metals At The H-12 Outfall Page: 3 of 16
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WSRC-TR-2005-00566
Executive Summary
The H-12 outfall cannot consistently meet the very low copper limit specified in SRS's
current NPDES permit. One treatment option that is under consideration consists of
diverting a portion (25%) of the H-12 flow through a peat bed and then blending the
outflow from the peat bed with the remainder of the H-12 discharge. Peat will not only
remove the copper from the portion of the effluent that is being treated, but will also
reduce the bioavailability and toxicity of any copper present in the blended effluent, due
to the leaching of dissolved organic carbon (DOC) from the peat. DOC binds metals
tightly so that they cannot be transported across the gill surfaces of aquatic organisms,
thereby decreasing their bioavailability and toxicity.
In order to assess the effectiveness of a peat bed for removing metals from H-12
effluent, a bench-scale laboratory study was conducted to determine removal efficiency.
Two sets of experiments were conducted. The first consisted of flowing H-12 effluent
through a peat bed and measuring copper concentrations in the inflow and outflow. In
the second experiment, copper was spiked into H-12 effluent to a concentration that
exceeds worst-case concentrations at H-12 and the spiked effluent was treated by the
peat bed. The results of both experiments indicate that copper in the peat bed effluent
was below the detection limit of 5 pg/L. DOC was increased by 137% after passage
through the peat. Based on historical data for H-12, when the treated effluent is blended
with untreated effluent at a ratio of 1:3, the resulting copper concentration should usually
be below the final NPDES limit of a monthly average of 6 pg/L.
The bioavailability of copper in the blended effluent was evaluated by performing copper
spiking toxicity tests on untreated and blended effluent. The results indicate that copper
bioavailability in the blended effluent was reduced by a factor of 9 (when compared to
untreated effluent). When compared to standard lab water, copper bioavailability in the
blended effluent was reduced by a factor of 2.7. These results suggest that it may be
possible to perform a Water Effects Ratio study at the H-12 outfall after construction of
the peat bed to obtain higher NPDES limits, if there is a need to do so.
Introduction
The H-12 National Pollutant Discharge Elimination System (NPDES) Outfall at the
Savannah River Site is periodically out of compliance with its revised copper limit in the
current NPDES permit. The H-12 discharge is composed of a number of contributing
sub-streams, and includes various cooling water sources, building discharges, and storm
water runoff. As part of the solution to avoid future exceedences, the construction of a
peat bed to treat a portion of the normal outfall discharge is being considered, both to
remove copper from the water and to improve the water characteristics by addition of
organic carbon to the waste stream. After treatment by the peat bed, the water would be
recombined with the untreated portion of the discharge prior to reaching the compliance
point. The new limit of 6 pg/L of copper that will go into effect in October 2008 may
necessitate conducting a water effects ratio test to request a higher copper limit at the H-
12 Outfall in the future.
Peat moss has a very high affinity for removing and holding metals and other cationic
elements in water (Brown et al. 2000; Kratochvil and Volesky 1998; Couillard 1994;
Veglio and Beolchini 1997). Metal removal is primarily through ion-exchange and2
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nelason eric. Bench-Scale Demonstration Of A Peat Bed For Removal Of Metals At The H-12 Outfall, report, December 30, 2005; [Aiken, South Carolina]. (https://digital.library.unt.edu/ark:/67531/metadc891559/m1/3/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.