Are you facing challenges with lower effluent phosphorus limits at your WRRF? YSI experts review phosphorus removal strategies in municipal wastewater applications. Phosphorus, primarily existing as phosphate, is a nutrient of concern for many wastewater operators. Effluent phosphorus limits continue to be lowered to protect our lakes and rivers from eutrophication. To meet these limits, operators need to improve treatment processes to remove phosphorus as efficiently as possible.

1. The Essentials
of Phosphorus Removal in Wastewater
Ben Barker,
Applications Engineer
Laura St. Pierre,
Product Segment Manager
April, 2020

2. I. The Science of Phosphorus
II. Phosphorus in Wastewater
III. Online Orthophosphate Monitoring
IV. Phosphorus Removal Strategies
V. Case-Studies
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3. 3
Part I:
The Science of Phosphorus

4. Phosphorus Chemistry
• Phosphorus is 1 of 5 main elements of living
organisms (CHONP)
• Nearly all forms of phosphorus in our environment
are a type of phosphate (PO4
3- ), Orthophosphate
ion
4
Sources: By NEUROtiker ⇌ - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=5064435
http://www.chemspider.com/Chemical-Structure.1032.html

5. Phosphorus Chemistry
• Phosphorus is 1 of 5 main elements of living
organisms (CHONP)
• Nearly all forms of phosphorus in our environment
are a type of phosphate (PO4
3- ), Orthophosphate ion
• Phosphates occur in several different places within
the human body
• Bones, DNA and RNA, Adenosine tri-phosphate (ATP)
• Excess phosphorus is processed by the kidneys and
discharged in urine/feces
5
Sources: By NEUROtiker ⇌ - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=5064435
http://www.chemspider.com/Chemical-Structure.1032.html

6. Phosphorus in the Ecosystem
• Phosphorus is the limiting nutrient in freshwater
systems
• Excess phosphorus causes eutrophication
• Harmful algal blooms (HABs)
• Oxygen dead zones
• Fish kills
• Water Resource Recovery Facilities (WRRFs)
are considered point sources for nutrients like
phosphorus
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7. 7
Part II:
Phosphorus in Wastewater

8. Water Quality – National Pollutant Discharge Elimination System
(NPDES)
• Eutrophication concerns in the late 1960’s
• 1972 Clean Water Act
• ~$350 billion were spent on the construction and operation of wastewater
treatment plants in the first 20 years
8
Sources: https://www.smithsonianmag.com/history/cuyahoga-river-caught-fire-least-dozen-
times-no-one-cared-until-1969-180972444/
(USGS, 1999)

9. NPDES Effect On Total Phosphorus Effluent Limits
• Total phosphorus effluent concentrations had
peaked around 1970 at 11 mg/L
• Banning phosphates in detergents and increased
secondary treatment resulted in total phosphorus
effluent concentrations down to 3-5 mg/L
• Further restrictions of effluent TP limits in key regions
set to 0.5-1.5 mg/L by 1999
• Today, TP effluent limits are being implemented in
new regions in the US and some are beginning to
achieve “ultra-low” limits (<0.1 mg/L TP)
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10. Phosphorus Forms in Wastewater
*All are different forms of PO4
3-
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11. Phosphorus Forms in Wastewater
*All are different forms of PO4
3-
11
Total
Phosphorus

12. Phosphorus Forms in Wastewater
Ortho-P
*All are different forms of PO4
3-
12
Total
Phosphorus

13. How is Phosphorus Removed?
1. Chemical Removal
2. Biological Removal
3. Tertiary Filtration
13
Basic Concept Requires:
Soluble ‘P’ ‘P’ Particulate Settling/Filtration
‘P’‘P’

14. Effluent
TP
WRRFs Are NOT Designed to Remove Phosphorus
14
Influent
Secondary
Effluent
TP
Secondary
Clarifiers
Biological
Transformation
and Mixing

15. Bio or
Chemical
P-Removal
Process with Phosphorus Removal
15
Effluent
TP
Secondary
Clarifiers
Secondary
Effluent
Influent
Biological
Transformation
and Mixing
Post P-Removal Process

16. Audience Poll Question #1
What is the Total Phosphorus effluent limit for your facility?
• >1 mg/L TP
• 0.1 – 1 mg/L TP
• <0.1 mg/L TP
• No TP limit
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17. 17
Part III:
Online Orthophosphate
Monitoring

18. Total Phosphorus vs Orthophosphate Measurements
Total Phosphorus
• Measurement of all phosphorus within a sample
• Steps:
1. Digestion of sample turning all phosphorus forms into orthophosphate
2. Colorimetric measurement ( or method)
Disadvantages – Sample processing is time consuming, requires additional equipment

19. Total Phosphorus vs Orthophosphate Measurements
Total Phosphorus
• Measurement of all phosphorus within a sample
• Steps:
1. Digestion of sample turning all phosphorus forms into orthophosphate
2. Colorimetric measurement ( or method)
Disadvantages – Sample processing is time consuming, requires
additional equipment
Orthophosphate
• Soluble Reactive Phosphorus only
• Steps:
1. Filter through 0.45 micron filter
2. Colorimetric measurement ( or method)
*Typically, an orthophosphate measurement is satisfactory for monitoring and control at WRRFs most of the TP
should be in the soluble form at facilities that remove phosphorus
Effluent
TP
Removed
by
Secondary
Clarifiers
Post P-Removal Process

20. Colorimetric Measurement of Ortho-P
20
Sample
(PO4
3-)
Reagent
Photometer
λ=420nm
method (SM 4500-P C)
• Detection limit = 0.02 mg P/L
• Used in most online analyzers
• Stable and repeatable method
• Laboratory method (more difficult measurement)
• Sample processing required for TP or sNRP
Mixing
Yellow
coloration

21. 4 Things to Consider When Reviewing Online Analyzers
21
1. Is it easy to use?
2. What maintenance is
required and who is going
to perform it?
3. And how much does it
cost to run the analyzer?
4. Is it easy to understand?

22. Orthophosphate Cabinet Analyzers
5 Main Components
22
• Electronics
• Reagent & Solutions
• Photometric Unit
• Pumps & Tubing
• Filter (not shown)

23. Analyzer Mounting
23

24. Sampling Filtering & Transport
24
Active
Passive

25. Alyza-PO4
• Automatic cleaning
• Automatic calibration – one or two
point
• Temperature control improves
accuracy
• Onboard Diagnostics
• ‘IV-style’ Chemical bag
• Small, easy to replace
• Exchange once per 6 months for PO4

26. 26
Orthophosphate:
• 5 µL per
measurement
• Less than 1 ml per
day at 10 minute
intervals

28. Part IV:
Phosphorus Removal
Strategies

29. Phosphorus Removal Strategies
29
1. Chemical Removal
• Addition of metal salts to react with soluble phosphate to form solid precipitates that are removed
by solids separation processes (clarification/filtration)
2. Enhanced Biological Phosphorus Removal
• Enhanced biological uptake of phosphorous by selected microorganisms called phosphorous
accumulating organisms (PAOs) that are removed by solids separation processes
3. Tertiary Filtration
• Post-secondary filtration process designed to remove phosphorus to ultra low levels (<0.1 mg/L)

30. Fe or Al
1. Addition of metal salt flocculent forms hydrous metal oxide (HMO) floc in basin
2. Mixing encourages HMO formation and reaction with P
3. Soluble P adsorbs to HMO reactive sites
4. HMO enmeshes colloidal & Particulate P
Chemical Removal
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31. Adsorbed
Soluble P
Enmeshed
Particulate P
1. Addition of metal salt flocculent forms hydrous metal oxide (HMO) floc in basin
2. Mixing encourages HMO formation and reaction with P
3. Soluble P adsorbs to HMO reactive sites
4. HMO enmeshes colloidal & Particulate P
Chemical Removal
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32. Chemical Removal: Particulate Form
32
Hydrous Metal Oxide flocs (HMOs)
produce a complex surface, creating
many binding sites for phosphate and
can trap particulate phosphorus
SEM image of 1-minute old (FeOH3) floc, Dr. Vladimir Kitaev, Wilfred
Laurier University

33. Chemical Removal: Particulate Form
33
Hydrous Metal Oxide flocs (HMOs)
produce a complex surface, creating
many binding sites for phosphate and
can trap particulate phosphorus
SEM image of 1-minute old (FeOH3) floc, Dr. Vladimir Kitaev, Wilfred
Laurier University
Metal Salt Flocculants
Alum (Aluminum sulfate): Al2(SO4)3 Sodium Aluminate: NaAlO2
Ferric (Ferric Chloride): FeCl3 Ferrous Chloride: FeCl2
Ferric Sulfate: Fe2(SO4)3 Ferrous: Sulfate: FeSO4

34. Chemical Removal: Simutaneous Precipitation
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35. Orthophosphate Set Point
35
Setpoint = 0.65 mg P/L

36. Chemical Dosing Control Types:
ON/OFF Control
• Feed valve is either fully open or closed based on setpoint
• Inefficient
Floating Control Setpoint
• 3-point control using an actuator
o Slowly open, slowly close, or hold
• Aims to hold P at setpoint, dosing least amount as possible
• More control =more efficiency
Proportional or Modulating Control
• Continuous control using an actuator
o Dosing is adjusted continuously based on difference between the reading and setpoint
• Continuous control= most efficient
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37. Enhanced Biological Phosphorus Removal
EBPR = Enhanced biological uptake of phosphorous by selected microorganisms called phosphorous
accumulating organisms (PAOs)
Anaerobic Phase
1. No dissolved oxygen or nitrate
2. Polyphosphate store released for Energy
3. Energy used to take up Volatile Fatty
Acids (VFAs) from water
4. Stored as Poly-Hydroxybutyrate (PHB)

38. Enhanced Biological Phosphorus Removal
EBPR = Enhanced biological uptake of phosphorous by selected microorganisms called phosphorous
accumulating organisms (PAOs)
Aerobic Phase
1. Dissolved oxygen present
2. DO and PHB metabolized for Energy
3. Energy used for reproduction
4. Energy used for Luxury Phosphorus Uptake

39. Enhanced Biological Phosphorus Removal: Particulate Form
39
(Günther et al, 2009)
Anaerobic Zone
DO, NO3
Aerobic
(DO)

40. Enhanced Biological Phosphorus Removal

41. Monitoring the EBPR process
Dissolved Oxygen (DO)
• Monitoring anaerobic and aerobic zone
Oxidation-Reduction Potential (ORP)
• Real-time control of EBPR process
COD /BOD
• Vital for maintaining the correct COD:P ratio in EBPR basins
Volatile Fatty Acids (VFAs)
• Required for effective EBPR process, can be added to process if needed
41

42. Tertiary Filtration
42
• A tertiary filtration process in combination with chemical or biological removal can
reduce total phosphorus to ultra low levels (<0.1 mg/L)
Common types of tertiary filtration:
• Sand-filtration
• Mixed-media filtration
• Cloth-media filtration
• Membrane filtration
• Disc filtration

43. Tertiary Filtration
43
(EPA, 2007)

44. Phosphorus Removal Processes: Pros and Cons
Chemical Removal Enhanced Biological
Phosphorus Removal
Tertiary Filtration
Pros Easy to implement
Low possibility of failure
Low operating cost Ultra low phosphorus levels
achievable
Cons Increased operating costs Large infrastructure
requirements
Influent water characteristic
requirements (COD:P ratio,
VFAs)
Must be used in
combination with another
removal process
Expensive to implement
44

45. Poll Question #2
45
What phosphorus removal strategies are you currently using or thinking about using?
Select all that apply:
• Biological-P Removal
• Chemical-P Removal
• Tertiary Filtration
• Don’t Know
• No plans to implement P-removal

46. Part V:
Case Studies

47. Watertown, WI
Floating Control Setpoint
47

48. Watertown, WI: Chemical Dosing System
48
Setpoint = 0.65 mg P/L

49. Watertown, WI: Chemical Usage
$0
$20,000
$40,000
$60,000
$80,000
$100,000
2011 2012 2013 2014
Ferric Chloride Costs
Annual expense
49
5.2 MGD plant with average flow of 3.0 MGD
Control using orthophosphate analyzer
Simple payback is 1 year or less
Limit at time = 1 mg/L TP
NOTE: Analyzer installed in 2012

50. Brookfield, WI
50
• 12.5 MGD plant
• 1.0 mg P/L total phosphorus discharge limit
• Dosed alum based on manual laboratory
samples
• Goal: Become more efficient with alum
dosing and prepare for future effluent limit
of 0.075 mg P/L

51. Brookfield, WI
51
• Result: Installed IQ orthophosphate analyzer
at treated effluent to automatically control
alum dosing at secondary treatment
• Chose YSI for the low maintenance required
of IQ analyzers:
• Low reagent consumption
• Auto-calibration
• Auto-cleaning

52. Brookfield, WI
52
Savings with Continuous Online Monitoring of Orthophosphate to
control chemical P-removal
Before IQ Analyzer After IQ Analyzer
Alum Usage 8,000 gallons/month 6,890 gallons/month
Cost for alum $10,000 per month $8,500 per month
Savings $1500 per month, $18,000
per year

53. ORP Control of EBPR: Greene County, OH
53
ORP High: ~250 mV
• Air off until + 50 mV
• Denitrification (DO and NO3 removed)
Anaerobic Timer: 40 min
• Anaerobic (no DO or NO3)
• P release
• Ends at around -50 mV
Anaerobic to Aerobic
• Air “on” until ~250 mV
• DO Setpoint: 1.7 to 1.9 mg/L
• Luxury P uptake
250 mv
Air “Off”
Air “On”
-50 mv
50 mv

54. 2009 – 1 mg/L TP Limit with EBPR
Smith, R.C., Goble, L, “To Everything There is a Season:
Lessons from Four Seasons of Phosphorus Removal at
Greene County Sugarcreek WRRF”, WEFTEC 2010
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55. Take Home Points
• Excess phosphorus causes eutrophication in lakes and reservoirs, having an
adverse effect on the ecosystem. Removing phosphorus from wastewater can help
mitigate these effects.
55

56. Take Home Points
• Excess phosphorus causes eutrophication in lakes and reservoirs, having an
adverse effect on the ecosystem. Removing phosphorus from wastewater can help
mitigate these effects.
• Chemical and biological removal converts soluble phosphorus to particulate
phosphorus, which can be removed from wastewater by settling or filtration.
56

57. Take Home Points
• Excess phosphorus causes eutrophication in lakes and reservoirs, having an
adverse effect on the ecosystem. Removing phosphorus from wastewater can help
mitigate these effects.
• Chemical and biological removal converts soluble phosphorus to particulate
phosphorus, which can be removed from wastewater by settling or filtration.
• Each phosphorus removal process has advantages and disadvantages, but
sometimes multiple processes will be needed to reduce TP below effluent limits
depending on your region.
57

59. Contact Us for More Information!
EMAIL:
laura.st.pierre@xyleminc.com
benjamin.barker@xyleminc.com
info@ysi.com
ONLINE:
YSI.com/IQSN
YouTube.com/YSIInc
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