Optimizing Chemical
Phosphorus Removal
JB Neethling
HDR Engineering
2013 Technical Conference and Exposition
Ohio Water Environment Association (OWEA)
Mason, OH
June 18-20, 2013
Copyright 2013 HDR Engineering,
Inc. All rights reserved.
Agenda
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Chemical Phosphorus Removal Basics
Phosphorus Species
Performance
Opportunities for Optimization
Phosphorus Species
Total P
Dissolved P
Ortho P
(Reactive P)
Inorganic
Condensed P
Particulate P
Soluble
Organic P
Particulate
Reactive P
Particulate
Acid Hyd P
Particulate
Organic P
Fundamental Principle of Phosphorus Removal
There is no airborne (gaseous) form of
phosphorus
Fundamental Principle of Phosphorus Removal
There is no airborne (gaseous) form of
phosphorus
The exception
Convert to Particulate
SolP
Liquid
Particulate P
Solid
Soluble P
Particulate P
Typical Chemical Treatment Opportunities
Primary
Secondary
Solids
Processing
Tertiary
Polish
Chemicals used for Phosphorus
Precipitation
Chemical
Formula
Aluminum
Sulfate (Alum)
Al2(SO4)3.14.3(H2O)
M.W. = 599.4
Removal
mechanism
Effect on pH
Metal hydroxides
removes
alkalinity
Metal hydroxides
removes
alkalinity
Poly Aluminum AlnCl(3n-m)(OH)m
Al12Cl12(OH)24
Chloride
Metal hydroxides
none
Ferrous sulfate Fe2SO4
(pickle liquor)
Metal hydroxides
Removes
alkalinity
Ferric Chloride FeCl3
M.W. = 162.3
Lime
CaO, Ca(OH)2
Insoluble precipitate Raises pH to
above 10
Ferric Reaction with Phosphorus
The following illustrates a “stoichiometric reaction”
of Fe+++ with P
FeCl3 + H3PO4 = FePO4 + 3HCl3
1 mole of Fe reacts with 1 mole P
5.2 mg ferric per mg P
0.92 mg alkalinity per mg of ferric
Alum Reaction with Phosphorus
The following illustrates a “stoichiometric reaction”
of Al+++ with P
Al2(SO4)3.14H2O+ 2H3PO4 
2AlPO4 + 3H2SO4 + 18H2O
2 mole of Al reacts with 2 mole P (or 1 mole Al per
mole P)
9.6 mg alum per mg P
0.5 mg alkalinity per mg of Alum
Phosphorus Concentration
Phosphorus Removal
Initial removal - Stoichiometric
1:1
Equilibrium control – need
higher dose
Break ~ 1 mg/L
Chemical Dose
Molar Dose Ratio From Tests
100
20
18
Full Scale 6.6 - 6.75
Lab data pH 6
Lab data pH 7.2
14
10
12
Fe/P (mol/mol)
Al/P (mol/mol)
16
10
8
6
1
4
Lab data pH 6.5
2
Lab data pH 6.8
Lab data pH 7.2
0
0.01
Lab data pH 8
0.1
1
ortho P res (mg/L)
10
Full Scale data
0.1
0.01
Slav Hermanowicz, Chemical Fundamentals of Phosphorus Precipitation,
WERF Boundary Condition Workshop, Washington DC, 2006
0.1
1
ortho P res (mg/L)
10
Exact Molar Ratios Versus Effluent Soluble P
will Vary with Applications
• 1.5 to 2.0 Molar ratios for 80-98 percent removal
• 5.0 to 7.0 Molar ratios for higher efficiency and to reach
low minimal soluble P concentrations
• Ratios are higher with PAC
• Factors that influence ratios
– pH
– Mixing method
– Wastewater characteristics
• Colloids and solids effect P-metal hydroxide
complexations
• Organic subtrates
• Iron and aluminum can react with humic substances
Kinetics and Mixing of Phosphorus / Alum
Reaction
Szabó et al. (2006) The Importance Of Slow Kinetic Reactions In Simultaneous
Chemical P Removal, WEFTEC 2006
Photomicrographs of Phosphate Precipitants
pH 7-->
← pH 3
Scott Smith, Wilfrid Laurier University
Fresh HFO
Scott Smith, Wilfrid Laurier University
Young HFO
FePO4 precipitant
After 4 days.
Scott Smith, Wilfrid Laurier University
Aged HFO
HFO precipitant
After 2 years.
Hard !!
Scott Smith, Wilfrid Laurier University
Metal Hydroxide Removal of P
Found for Ferric Addition
• Metal hydroxide formed
• Co precipitation of P into hydrous ferric oxides structure
– Fe(OH)3, Fe(OH)4-
• Surface complexation between P and metal hydroxide
compounds
• Phosphorus and Iron share oxygen molecule:
• FeOOH + HOPO3 = FeOOPO3 + H2O
• Hydroxide formation can be simply represented:
– FeCl3 + 3H2O => Fe(OH)3 + 3 HCl
– Al2(SO4)3.14H2O + 3 H2O => 2Al(OH)3(s) + 3H2SO4
Closer Look at the
Chemical Species
33
Phosphorus Speciation
and Removal in
Advanced Wastewater
Treatment
L. Liu, D. S. Smith, D. Houweling
J.B. Neethling, H.D. Stensel
S. Murthy, Amit Pramanik and A. Z. Gu
Analytical Definitions of Phosphorus Species
• Filterable/nonfilterable (soluble?)
– Passing through filter paper
– Could be colloidal (very small particles)
• Reactivity to analytical procedure
– Measure for orthophosphate
• Pretreatment (acid hydrylosis, digestion, etc)
– Convert larger molecules to be reactive
(orthophosphate)
Phosphorus Species Categories
Total P
Dissolved P
Ortho P
(Reactive P)
Inorganic
Condensed P
Particulate P
Soluble
Organic P
Particulate
Reactive P
Particulate
Acid Hyd P
Particulate
Organic P
Particulate Chemical Precipitant Measures as
Reactive P
Combine d Se condary Efflue ntJar Te sting Re sults
P in=0.31mg/L
0.35
Effluent ortho-P (mg/L)
0.3
0.25
unf iltered
0.2
0.15
Filtered
0.1
0.05
0
0
10
20
30
40
Alum Dose-Al2(SO4) 3.14H2O (m g/L)
50
Method
Analytical Definition Based Phosphorus
Fractions/Species
Total P
Dissolved P
Sol Reactive P
SRP
Sol Acid
Hydrolyzable
Particulate P
Sol
Dig.
PRP
Part Acid
H.
Particle Digestible
Ortho P
Inorganic
Condensed P
Sol
Org
Particulate Organic P
Colloidal P
Chemical particulate P
Nonreactive Phosphorus
Total P
Dissolved P
Sol Reactive P
SRP
Sol NonReactive P
SNRP
Total Reactive P
Particulate P
PRP
Particulate NonReactive P
Total NonReactive P
Analytical Definition Based Phosphorus
Fractions/Species
Total P
Dissolved P
Sol Reactive P
SRP
Ortho P
Particulate P
Sol Non Reactive P
sNRP
Acid Hydrolyzable
P
Sol
Org
Part Chemical P
Colloidal P
Part Organic P
Secondary Effluent TSS adds to Particulate NRP
3%
160
Particulate Nonreactive Phosphorus, ug/L
160
140
120
100
1.5%
80
60
40
20
0
0
1
2
3
4
5
6
TSS, mg/L
1.0%
1.5%
2.0%
2.5%
3.0%
5
Filtered Effluent TSS adds to Particulate NRP
35 ug/L
Particulate Nonreactive Phosphorus, ug/L
35
3%
30
25
20
1.5%
15
10
5
0
0
0.2
0.4
0.6
0.8
1
1.2
TSS, mg/L
1.0%
1.5%
2.0%
2.5%
3.0%
1 mg/L
Pilot Study Results Illustrated Challenges at
Limits of Technology
•
0.09
0.08
Phophorus [mg/L]
0.07
•
0.06
0.05
0.04
No Treatment
Technology Available
for SNRP
Portion May Not Be
Bioavailable /
Biodegradable
0.03
0.02
0.01
0.00
DSBP
THS-1
sRP
Neethling et al, 2007
ZW-500
sNRP
pP
DSD2
Particulate P
Soluble
NonReactive P
Soluble Reactive P
Effluent P Fractions From Advanced Tertiary
Treatment Processes
P Concentration, mg/L
0.050
Sedimentation
Membrane
Filtration
0.040
0.030
0.020
Filtration
pAHP
pOP
pRP
sAHP
0.010
DOP
0.000
sRP
Lui, Gu, et al. (ongoing) Phosphorus Speciation and Removal in
Advanced Wastewater Treatment, WERF Report
P fractions at Plant N
P concentration (mg/L)
3.0
0.20
2.5
pOP
0.15
2.0
pAHP
0.10
pRP
1.5
0.05
1.0
DOP
0.00
0.5
sAHP
sRP
0.0
BNR INF
BNR
Chemical P
removal
Mono/Dual
media
Filtration
• sAHP seems to remain after BNR, associated with biomolecules
• Chemical addition converts sRP into pRP
• Chemical sRP (PO4) removal relies pRP removal
P concentration (mg/L)
Comparison of P fractions at Plant P
9
8
7
6
5
4
3
2
1
0
BNR INF
0.35
0.035
0.30
0.030
0.25
0.025
pOP
0.20
0.020
pAHP
0.15
0.015
0.10
0.010
0.05
0.005
0.00
0.000
BNR Eff
BNR
pRP
DOP
sAHP
sRP
Trident HS
• Plant P and N are similar as (BNR+sedimentation +Filtration): composition very
different
• DOP dominant soluble fraction; pAHP major particulate form
• Multi stage barrier remove TP to lower level
Opportunities for
Optimization
Opportunities for Improvement
• Improve understanding of chemical kinetics
– Dose relationships
– Reuse formed metal hydroxides
• Enhance solids separation
Molar Dose Ratio From Tests
100
20
18
Full Scale 6.6 - 6.75
Lab data pH 6
Lab data pH 7.2
14
10
12
Fe/P (mol/mol)
Al/P (mol/mol)
16
10
8
6
1
4
Lab data pH 6.5
2
Lab data pH 6.8
Lab data pH 7.2
0
0.01
Lab data pH 8
0.1
1
ortho P res (mg/L)
10
Full Scale data
0.1
0.01
Slav Hermanowicz, Chemical Fundamentals of Phosphorus Precipitation,
WERF Boundary Condition Workshop, Washington DC, 2006
0.1
1
ortho P res (mg/L)
10
Single Step Chemical Addition
Requires High Dose
P entering
mg/L
One
Step
5
P residual
mg/L
0.1
Alum/P dose
mol/mol
5
Alum/P dose
mg/mg
48
Alum dose
mg/L
235
Two Step Chemical Addition Reduce Dose
P entering
mg/L
One
Two
Step Step 1 Step 2 Steps
5
5
1
5
P residual
mg/L
0.1
1
0.1
0.1
Alum/P dose
mol/mol
5
1.5
5
2.1
Alum/P dose
mg/mg
48
14
48
21
Alum dose
mg/L
235
58
43
101
Two Step Chemical Addition Reduce Dose
P entering
mg/L
One
Two
Step Step 1 Step 2 Steps
5
5
1
5
P residual
mg/L
0.1
1
0.1
0.1
Alum/P dose
mol/mol
5
1.5
5
2.1
Alum/P dose
mg/mg
48
14
48
21
Alum dose
mg/L
235
58
43
101
Reuse Chemical Sludge to Reduce Dose and
Increase Reliability
• Return chemical sludge to upstream process
• Build solids inventory – operate in solids contact
mode
Conventional Tertiary Chemical P Removal
Al/Fe
PCL
AS
SCL
Al/Fe
SCL
Filter
“ReUse” Chemical Sludge Upstream
Al/Fe
PCL
AS
SCL
Al/Fe
SCL
Filter
Contact Clarification in Tertiary
Al/Fe
PCL
AS
SCL
Al/Fe
ANX
SCL
Filter
Coeur d’Alene: Microfiltration and Solids Recycle
Al/Fe
PCL
AS
SCL
Al/Fe
ANX
TMF
Implications for Design and Operation –
Coeur d’Alene Pilot
No Solids Inventory
Loss of
Alum feed
Implications for Design and Operation –
Coeur d’Alene Pilot
1.00
1.0
0.90
0.9
0.80
0.8
0.70
0.7
0.60
0.6
0.50
0.5
0.40
0.4
Alum Off
0.30
0.3
Alum On
0.20
0.2
0.10
0.1
0.00
10-Jun
10-Jun
11-Jun
11-Jun
12-Jun
TMF Effluent PO4-P
12-Jun
13-Jun
13-Jun
14-Jun
Secondary Effluent PO4-P
14-Jun
0.0
15-Jun
SE PO4-P [mg/L]
PO4-P [mg/L]
With Solids Inventory
Summary and Conclusion - I
• Chemical reactions for phosphorus removal with
ferric or alum is a primarily a surface complexation
reaction
• Good mixing and contact time is needed to
maximize chemical efficiency
• Preformed Metal Hydroxides retain the ability to
react and remove phosphate
Summary and Conclusion - II
• Target phosphorus species for effective removal:
– Precipitate Reactive Phosphorus – Phosphate
• Increased dose can improve removal
– Filter particulate fractions
• High efficiency filters
– Soluble Non-Reactive P remains difficult to remove
• Reuse metal hydroxides to reduce chemical use
Optimizing Chemical
Phosphorus Removal
JB Neethling
HDR Engineering
2013 Technical Conference and Exposition
Ohio Water Environment Association (OWEA)
Mason, OH
June 18-20, 2013
Copyright 2013 HDR Engineering,
Inc. All rights reserved.