Scorecard for Chemical
Treatments to Control Nutrients in
Surface Water Restorations in
Florida
Vickie Hoge
St. Johns River
Water Management District
Ann Shortelle, Ph.D. and Erik Makus
MACTEC Engineering and Consulting, Inc.
Chemical Treatments for
Nutrient Control
• Metallic salts
• Water treatment residuals – WTR’s
• Polymers
Metallic Salts for Nutrient
Removal
•
•
•
•
•
•
Aluminum sulfate (alum)
Polyaluminum hydroxychlorides (PACl)
Ferric sulfate
Ferric chloride
Sodium aluminate
Lime
Typical Precipitation (Alum)
Al+3 + 3H2O <-> Al(OH)3 + 3H+
Al2(SO4)3 + 2H3PO4 <-> 2AlPO4 + 3H2SO4
• If sufficient alkalinity is present, the acidity
will be neutralized
• AlPO4 precipitates
• Sorption of P onto the surface of Al
hydroxide polymers (floc)
• Entrapment/sedimentation of particulate
P by floc
Progressive Improvement –
Nutrient Reduction and Water Clarity
Application Methods
•
•
•
•
•
Barge
Marsh Master
Airboat
Injection
Land (via spreader)
Logistical Challenges
Removal Efficiencies Among Selected BMPs
Weighted Average Removal Efficiency (%)
# BMP
Studies
TSS
TN
TP
4
77
-2
22
10
33
-33
-270
Hydrodynamic Devices
9
2
2
0
Media Filter System
4
52
26
36
Periphyton Filters
1
35
12
17
Wetland Treatment
8
48
-8
31
Porous Pavement
2
-67
-16
18
22
49
26
61
Hydrodynamic Devices (Alum Enhanced)
2
-78
16
38
Wet Detention with Alum
3
57
14
50
Alum Injection Systems (Harper 1990)
-
89
78
89
BMP Category (FDEP 2007)
Dry Detention
Grassed Swales
Wet Detention
Eustis Muck Farm – P Species
5
TP-T
4
PO4-D
3
TP-D
2
1
Oct-04
Oct-03
Oct-02
Oct-01
Oct-00
Oct-99
Oct-98
Oct-97
Oct-96
Oct-95
0
Oct-94
mg TP/L
Alum / Sodium
Aluminate Application
S N Knight North – P Species
Alum
Application
0.25
PO4-D
TP-D
TP-T
0.15
0.10
0.05
Jul-05
Apr-05
Jan-05
Oct-04
Jul-04
Apr-04
Jan-04
Oct-03
Jul-03
Apr-03
Jan-03
0.00
Oct-02
mg/L
0.20
Solubility of Aluminum Species as Function
of pH and Relationship to Toxicity
-5
0
[Alt]
pC
[Al(OH)3]
[Al(OH)2+1]
[Al(OH)4-1]
5
[Al2(OH)2+4]
[Al+3]
[Al(OH)+2]
10
2
4
6
pH
8
10
12
Reducing potential toxicity
of aluminum
• Adaptive management of
pH
• Bench scale testing of site
water
• In small ponds, treat in
stages to allow fish
movement away from floc
• Molluscs may be sensitive
• Is bedding of floc an
issue?
• Al toxicity to humans – fact
or perception?
Dissolved Al and pH
Eustis Muck Farm, pH & Al-D
A l-D
8
300
6
200
4
100
2
0
0
Apr-04
Feb-04
Long Farm, pH & Al-D
Nov-04
400
Aug-04
10
Nov-03
500
Jun-03
ug Al-D/L
pH
A l-D
1400
1200
1000
800
600
400
200
0
11
10
9
8
7
6
May-05
Feb-05
Jul-04
Jan-04
5
Jun-03
ug Al-D/L
pH
Treatment Dosing Design
• Site-specific
• Benchscale testing
• Mesocosms or field
trials
Photo courtesy of DB Environmental
Design – Information Requirements
•
•
•
•
•
•
•
Background water quality
Soil or sediment nutrient concentrations
Water quality target
Site accessibility
Space availability
Floc retention and disposal
Vegetation and/or sediment disruption during
application
Design Issues - Injectors
• Lengthy distribution lines
• Adequate area to incorporate a settling
basin
• Automatic floc collection system
• Pump sizing and performance
• Effects of weather on design
• Permitting can take longer than
expected
Permitting Constraints - FDEP
• pH maintained between 6 and 7
• Minimum one minute mixing time before
floc reaches settling basin
• Floc must be disposed of properly
• No discharge of floc to waters of the
State unless there is no other choice
• Whole waterbody applications vs.
injections
Floc Fate – Proper Disposal or
Reuse
• Sanitary sewer
• Collection
systems
• Resource vs.
waste
Floc Disposal (fate) Issues
• The FDEP always wants to have floc
completely removed and not discharged into
receiving water.
• However, some SJRWMD permits (typically
older ones) did not have this as a
requirement.
• Currently, all systems are required to collect
and remove all floc, usually in a settling basin
prior to discharge into the receiving water
body, unless a feasibility study has
demonstrated that this is not possible.
Floc Disposal Issues (cont.)
• If floc is to be discharged to the
receiving water, then extensive
monitoring (water quality,
macroinvertebrates, etc.) must be
carried out.
• At a predetermined level, the entire
volume of settled floc must be removed
from the lake.
Operation Issues
Proper design – buffer required?
Proper dosage
Trained staff
Access
Chemical delivery and storage
O&M Issues: Alum Injection
Stormwater Treatment
Systems
•
•
•
•
Range: $10,000 to $50,000 annually.
Actual cost depends heavily on rainfall.
Long lines can create more difficulty.
Pumps for alum system are difficult to
regulate
Typical Cost per Mass P
Removed ($/kg)
Method
Alum injection
Barge application
Alum residual
$/kg P removed
~ 200 - 500+
~ 30
~ 60
Scorecard – Alum Injection
Item
Removal Efficiency
++
9
+
-
9
9
Ease: Permitting
9
Ease: Operation
Value (Cost)
--
9
Toxicity
Ease: Design
0
9
9
9
Scorecard – Alum Application
Item
Removal Efficiency
++
9
+
9
Toxicity
9
Ease: Design
Ease: Permitting
9
9
Ease: Operation
Value (Cost)
0
9
-
--
Questions?
January 24, 2006
Before
January 27, 2006
After