Transcript Document

ENVE5504 – Surface Water Quality Modeling
Case History
Sediment Redox Processes
and Mercury Management
in Onondaga Lake, New York
C
O
N
S
Hg
Testimony to the U.S. Senate has
described Onondaga Lake as one of
the most polluted in the country –
perhaps the most polluted.
Hennigan, R.D., 1990. America's Dirtiest Lake. Clearwaters 19: 8-13.
Syracuse, New York: The Salt City
• 1615 – first European visitor, Samuel Champlain
• 1654 – salt springs discovered, Father Simon Lemoyne
• 1794 – salt industry in place, James Geddes
• 1820 – local brine springs failing
• 1838 – wells dug around Onondaga Lake fail to locate source
• 1862 – salt industry reaches its peak
The Solvay Process
In 1865, a Belgian chemist, Ernest Solvay,
developed a process to produce soda ash from
calcium carbonate (limestone) and sodium chloride
(salt). Soda ash is used in softening water and in
the manufacture of glass, soap and paper:
CaCO3  2NaCl  Na2CO3  CaCl2
Ernest Solvay
1943: wastebeds collapse flooding
region with soda ash waste
http://pubs.acs.org/subscribe/journals/tcaw/11/i02/html/02chemchron.html
Solvay Process  Allied Chemical  Allied Signal  Honeywell
1884
soda ash production begins on west shore using locally
produced salt brine and limestone from nearby Dewitt
1880s
salt production moved to Tully Valley
1912
limestone quarries moved to Jamesville
1986
industry closes
The Chlor-Alkali Process
The mercury cell chlor-alkali process was used to produce chlorine gas
and sodium hydroxide through electrolysis of a salt brine solution.
Cl2
+
anode
26% NaCl
24% NaCl
Hg cathode
sodium amalgum, NaHg
H2
Hg
carbon
electrode
50% NaOH
H2O
2NaCl(aq)  2H2O(l )  2NaOH( aq)  Cl2( g )  H2( g )
The Chlor-Alkali Process
There is loss of mercury through leakage and dumping as the cells are cleaned
or replaced. Approximately 75,000 kg of mercury were discharged to Onondaga
Lake over the period 1946-1970.
mg∙kgDW-1
75
0
Adapted from Atlantic States Legal Foundation
http://www.aslf.org/ONONDAGALAKE/gallery1.html
Hg(0) – mercury can be present as elemental or metallic mercury, a form that
is subject to volatilization and release to the atmosphere;
Hg(II) – mercury can be present in ionic form, associated with salts and
existing in equilibrium with Hg(0);
MeHg, (Me)2Hg – mercury may be present in the mono- and dimethyl forms,
readily available for biotic uptake and produced from ionic mercury by sulfatereducing bacteria.
Hg (0)  Hg ( II )  MeHg
Source: Global Mercury Assessment, United Nations Environment Programme
http://www.chem.unep.ch/mercury/Report/GMA-report-TOC.htm
75
mg∙kgDW-1
0
Adapted from Atlantic States Legal Foundation
http://www.aslf.org/ONONDAGALAKE/gallery1.html
Superfund
MSNBC, 16 October 2006
Dredge and Cap: the plan includes dredging of 2.65 million cubic yards of
contaminated sediment with capping of 579 acres (20%) of the lake bottom.
Superfund
-Closure of the Allied Signal chloralkali plants
-Bottom sediments and adjacent sites
were assigned to the Federal
Superfund National Priorities List
-Clean-up of upland sites has been
completed wherein 8,500 tons of soil
were treated
-Wetland restoration was completed in
2007
-Groundwater Collection
System/Barrier Wall—barrier wall
construction has begun and
groundwater treatment is in progress
Innovative Soil Washing
Technology
Sediment Remediation Plan: dredge and cap, 20%
Sediment Remediation Plan: the other 80%
Monitored Natural Recovery
EPA does not consider monitored natural recovery to be a ‘no-action’
alternative, but rather an alternative means of achieving remediation objectives
(U.S. EPA 1999). Selection of this approach implies that contaminant
degradation and/or sequestration will eventually lead to remediation of the
sediment environment (U.S. EPA 2005) and restoration of lost beneficial uses.
The Mercury Cycle
Monitored Natural Recovery
• fully protective of human
health and the environment
me-Hg
Hg(0)
• objectives achieved in a
reasonable time
SRB
Enhanced Natural Recovery
• where MNR guidelines are not
met, consider in situ approaches
to reduce risk as sediments
proceed toward a new SS
following source controls.
SRB
Hg(II)
Hgp
complexation - sequestration
Chemical Augmentation
• oxygen
• nitrate
Mercury Sulfur Interactions
Methylmercury production is associated with the activities
of sulfate reducing bacteria.
20
8
15
6
10
4
5
2
0
0
J
A
S
ngMeHgL-1
mgS2-L-1
C(H2O)  SO42  H2 S  CO2  H2O
O
Source: Matilainen, T. 1995. Involvement of bacteria in methylmercury formation in anaerobic lake waters. J WAS, Vol. 80.
Data from Dave Matthews, Upstate Freshwater Institute (S) and Svetoslava Todorova, Syracuse University (Hg)
Sulfur and the Ecological Redox Series
C(H2O)
O2
NO3
SO4
 CO2  H2O  
Sulfur and the Ecological Redox Series
O2
C(H2O)
NO3
SO4
 N2  CO2  HCO3  H2O  
Sulfur and the Ecological Redox Series
O2
NO3
C(H2O)
SO4
 H2 S  CO2  H2O  
Redox Manifestations in Onondaga Lake
Oxygen
10
5
0
2.0
mgN-L-1
The depletion of alternate electron
acceptors (oxygen and nitrate) and
the accumulation of an endproduct of sulfate reduction
(hydrogen sulfide) in the
hypolimnion of Onondaga Lake
tracks the ecological redox series.
mgO2L-1
15
1.5
1.0
0.5
Nitrate
mgS2-L-1
0.0
6
4
2
Hydrogen
Sulfide
0
Data from Dave Matthews, Upstate Freshwater Institute
A
M
J
J
A
S
Oxygenation and Nitrate Augmentation
Nitrate augmentation is one means of
blocking sulfate reduction and the
attendant production of
methylmercury.
mgO2L-1
15
Oxygen
10
5
0
mgN-L-1
2.0
1.5
1.0
0.5
Nitrate
0.0
mgS2-L-1
6
4
2
Hydrogen
Sulfide
0
Data from Dave Matthews, Upstate Freshwater Institute
A
M
J
J
A
S
Mapping Diagenesis
various
electron
electron
 CO2 +
+
acceptor
donor
various
reduced species
end product
C( H2O)  O2  CO2  H2O
C(H2O)  Fe3  Fe2  CO2  H2O
C(H2O)  NO3  N2  CO2  HCO3  H2O
C( H2O)  SO42  H2 S  CO2  H2O
C( H2O)  Mn4  Mn2  CO2  H2O
C( H 2O)  CH4  CO2
Sediment Profiles
0
-2
8
18
28
38
48
58
2
4
6
8
10
Measuring Methylmercury Flux
1. Determine the MeHg flux from the sediments with the nitrate
concentration in the hypolimnion maintained at 2 mg/L.
2. Describe setup and conditions for the laboratory measurements.
3. Write the equation that will yield the desired flux and identify the
source of the input terms to that equation.
J
Measuring Methylmercury Flux
Feed
Stock
Q∙Cin
Q∙C
J
EXPERIMENTAL SET-UP
Results
dC
V
 Q  Cin  Q  C  J  A
dt
Flow (mL∙min -1)
1.0
0.8
Q
0.6
0.4
0.2
0.0
0
J
0.3
Q
 Css
A
0.2
Css
0.1
2
1
0
1
3
4
5
6
4
5
6
Days
0
EXPERIMENTAL SET-UP
2
0.0
2
4
Days
6
12
Oxygen (mg O2.L-1)
J
6
3
Nitrate (mgN∙L-1)
Q∙C
MeHg (ng.L-1 )
Q∙Cin
4
Days
0.4
Feed
Stock
2
10
8
6
4
2
0
1
2
3
Days
Results
150
120
ng.m-2.d-1
90
60
30
0
Hypolimnetic
Accumulation Rates
Porewater
Calculations
Flow-through No/No
Results
200
160
ng.m-2.d-1
120
80
40
0
Hi O2 +
Hi NO3
Low O2
+ NO3
No/No
O2
NO3
Application
0
0
3
6
9
12
15
Net demethylation
10
20
30
40
50
60
70
80
90
100
Sulfate Reduction and Methylmercury Production