Phosphorus
Removal
Sidney Innerebner, PhD, PE CWP
Indigo Water Group
Littleton, Colorado
-
Agenda
Biological Phosphorus Removal
Fundamentals
Impact of Operational Variables
Chemical Phosphorus Removal
2
-
If BOD5 is 250 mg/L,
then P should be
(250)•(0.02) = 5.0 mg/L
(250)•(0.05) = 12.5 mg/L
Rule of Thumb
Influent concentrations between 4 and
12 mg/L as P are typical
Ratio of P/cBOD5 for domestic
wastewater is 0.02 to 0.05
Flip it and cBOD5/P is 20:1 to 50:1
Higher ratios may indicate
Corrosion control additives
Recycle Streams
Septic, and/or
Industrial Waste
3
-
Phosphorus Fractionation
Phosphate
Polyphosphate
Organic
Phosphorus
~50%
Soluble
Ortho-P ~37%
Soluble
Poly-P
~12.5%
Organic
Note: Organic P may
be particulate or
soluble, biodegradable
or not.
-
Phosphate or Phosphorus as P?
Phosphorus is PO4
One Phosphorus atom
Four Oxygen atoms (1)(31 g/mole) = 31 g/mole (4)(16 g/mole) = 64 g/mole
95 g/mole total
1 g P
31 g P
1 mole P
1 mole P
1 mole PO4
1 mole PO4
95 g PO4 = 3.07 g PO4
Laboratories are not consistent when reporting phosphorus.
-
Practice Problem:
A student reported that the analyzed
wastewater contains 18 mg/L of
orthophosphate. What is the concentration
if it is reported as P?
(a) 6
(b) 10
(c) 18
(d) 24
-
Phosphorus Removal
Biological and Chemical Methods
Assimilative Uptake
EBPR uses PAO’s to uptake phosphorus
Levels down to 0.7 mg/L PO4-P (as P)
Chemical method uses alum or ferric
chloride to precipitate phosphorus
Levels down to 0.03 mg/L PO4-P (as P)
Methods often used in combination
7
-
Composition of a Cell Results in
Assimilative Uptake of N and P
8
All living things contain
nitrogen and phosphorus
Cells are between 6 and
12% Nitrogen by weight
Normally between 1 and
2% Phosphorus by weight
PAOs contain up to 40%
Phosphorus by weight
Nitrogen
Phosphorus
Other
-
Phosphorus Concentrations
Decrease with Treatment
Location Typical P, mg/L
Raw Sewage 4 – 12
Primary Effluent 2.5 – 8
Secondary Effluent w/o Bio-P 2 – 5
Secondary Effluent with Bio-P 0.7 – 1.0
Tertiary Filter Effluent 0.03 – 0.05
9
Wasting 1.5 – 2% P sludge reduces P by 10-30% in a non-BioP WWTP
-
Enhanced Biological
Phosphorus Removal (EBPR)
A two-step process of phosphorus release and uptake under alternating anaerobic and aerobic or anoxic conditions
Special bacteria call Phosphate Accumulating Organisms or PAOs
Luxury uptake of phosphorus
Normal cells have 1-2% P
PAOs can have up to 40%
PAOs can make MLVSS between 4 and 8% P
WAS removes P from the system
10
-
Characteristics of Phosphorus
Accumulating Organisms
Acinetobacter
Heterotrophic
Facultative (use oxygen or nitrate)
Use readily biodegradable cBOD
Store poly-ß-hydroxybutyrate (PHB), PHA,
glycogen, and other intermediate
compounds
Store energy as poly-P – e.g. luxury uptake
11
PAOs Must Cycle Between Anaerobic
and Aerobic/Anoxic Zones
12
PHB
Poly-P
Volatile Fatty Acids
Phosphate
Energy
PHB
Poly-P
Phosphate
Oxygen
Carbon Dioxide +H2O
Energy
(Nitrate)
Glycogen
Glycogen
-
Poly-P Acts Like a Battery
Storing and Releasing Energy
13
http://blogs.s60.com/tommi/2007/04/could_the_battery_life_challen.html
PAOs Must Cycle Between Anaerobic
and Aerobic/Anoxic Zones
14
PHB
Poly-P
Volatile Fatty Acids
Phosphate
Energy
PHB
Poly-P
Phosphate
Oxygen
Carbon Dioxide +H2O
Energy
(Nitrate)
Glycogen
Glycogen
-
Anoxic Aerobic
An
ae
rob
ic
Anaerobic
- VFAs
created
- Uptake VFAs
- Release P
- Store PHB
Anoxic /
Aerobic
- Uptake P
- Use PHB
P Leaves Here
Three-Stage BNR
-
Poly-P
Poly-P
PHB
PAO’s with Inclusions
16
Thank you to
James Barnard
with Black and
Veatch for use
of these images.
-
Poly-P
Tons of Poly-P per PAO
17
Thank you to
James Barnard
with Black and
Veatch for use
of these images.
-
O
O
Bio-P or EBPR Requires Mg++ & K+
Sufficient organic carbon and P
Correctly sized anaerobic reactor
Forces P Release
Produces fermentation products
Sufficient amounts of Mg++ and K+
Mg++
K+
P
O
O
18
-
Anoxic Aerobic
An
ae
rob
ic
Anaerobic
- VFAs
created
- Uptake VFAs
- Release P
- Store PHB
Anoxic /
Aerobic
- Uptake P
- Use PHB
P Leaves Here
Three-Stage BNR
-
Modified University of
Cape Town or UCT
1st
Anoxic
2nd
Anoxic
An
ae
rob
ic
Aerobic
EBPR can be done by cycling from anaerobic to anoxic.
UCT protects anaerobic zone from excessive nitrate.
-
Five-Stage Bardenpho
Pre-
Anoxic
First
Aerobic
Post-
Anoxic 2n
d
Ae
rob
ic
Achievable Effluent TN of 3 mg/L - LOT
An
ae
rob
ic
Methanol
(optional)
TP of 0.7 mg/L - LOT
Total nitrogen removal of 80 – 90%
-
Typical P Profile
Source: Wu, Chang-Yong, Yong-Zhen Peng, Shu-Ying Wang, Yong Ma (2010) Enhanced Biological Phosphorus
Removal by Granular Sludge: From Macro to Micro Scale. Water Research. Vol 44 (3) 807-8144
-
Major Reactions in Each Zone
Process or
Compound
Anaerobic Zone Aerobic and/or
Anoxic Zone
Readily
Available
Substrate - VFAs
Taken Up Stored VFAs
Consumed
Phosphate Released Taken Up
Magnesium and
Potassium
Released Taken Up
PHA & PHB Stored Oxidized
Glycogen Used Restored
23
-
Benefits of Bio-P
Reduced sludge production
over chemical phosphorus
removal
Reduces chemical dose
Improved sludge settleability
and dewatering characteristics
Reduced oxygen requirement
Reduced process alkalinity
requirements
Farmers LOVE Bio-P Biosolids
24
-
Operational Considerations
Influent COD:P Ratio Critical
Dissolved oxygen
pH and Temperature
Solids Retention Time (SRT)
Hydraulic Retention Time (HRT)
Competing Organisms – GAOs and
Denitrifiers
25
-
Minimum COD:TP Ratios
Parameters Recommended Minimum Ratio
COD:TP 40 – 45
cBOD:TP 20
rbCOD:TP 1, 2 10 – 16
VFA:TP 4 - 16
1 Most Accurate Predictor 2 May vary considerably by season in temperate climates
COD = Chemical Oxygen Demand, TP = Total Phosphorus, BOD = Biochemical Oxygen Demand,
rbCOD = readily biodegradable COD, VFA = Volatile Fatty Acid
Source: EPA/600/R-10/100 (August 2010)
-
Influent COD:TP Ratio vs Effluent TP
-
Influent cBOD:TP Ratio vs Effluent TP
-
COD:TP Ratio versus %P in MLVSS
More
Assimilative
Uptake
Higher Eff P
Conc.
-
Influent COD
Sti
Unbiodegradable COD
Sui
Biodegradable COD
Sbi
Soluble readily
biodegradable
COD
Sbsi
Particulate
Slowly
biodegradable
COD
Sbpi
Soluble
unbiodegradable
COD
Susi
Particulate
unbiodegradable
COD
Supi
Soluble, readily biodegradable COD is CRITICAL for BNR Breaks down to VFAs in anaerobic zone.
-
Volatile Fatty Acids
Short chain hydrocarbons – less than 6 carbons
Acetic , propionic, butyric, valeric, caproic acids
Other unsaturated forms
Easily taken up by PAOs and denitrifiers
How much do you need in anaerobic zone?
Ekama (1984) – 25 mg/L
Others – 60 mg/L
May vary from 25 – 125 mg/L seasonally.
-
Estimating Readily
Biodegradable COD
Collect samples from influent and effluent
of BNR process
Analysis steps
Flocculation with zinc sulfate
Filtration***
COD analysis
𝑆𝑏𝑠𝑖 = 𝑠𝐶𝑂𝐷 − 𝑆𝑢𝑠𝑖
-
What it all means
Readily
biodegradable
soluble COD
Total
soluble
COD
Soluble
inert COD Sbsi = sCOD - Susi
-
Analytical Procedure
Add 1 mL of 100 g/L zinc sulfate to a 100 mL
wastewater sample.
Mix with magnetic stirrer for 1 minute.
Adjust pH to 10.5 with 6-M sodium hydroxide (NaOH)
Settle for a few minutes
Withdraw clear supernatant
Filter through acid-washed 0.45 um filter*
Measure COD by normal method
Source: MOP29 (2005), page 447
-
Not Just rbCOD – PAOs Really Need
Volatile Fatty Acids (VFAs)
Acetic Acid
Propionic Acid
Butyric Acid
Isobutyric Acid
Others
35
-
Volatile Fatty Acids Can Come
From Several Sources
Collection system fermentation
Primary clarifier fermentation
0.066 – 0.15 g VFA/g total solids
Anaerobic zone
Oversize slightly
On-site fermenters
4 – 8 days in anaerobic gravity thickener
Supplemental VFAs (mix of acetic,
propionic, others)
36
-
Collection System Odor Control
-
Glycogen Accumulating
Organisms
GAOs can uptake VFAs in anaerobic zone
No luxury uptake of phosphorus
Compete with PAOs for resources
Source: Whang, Liang-Ming (2008) Competition Between Polyphophate- and Glycogen-Accumulating Organisms in Enhanced Biological Phosphorus Removal (EBPR) Systems Vol 4(8)
-
Conditions Favoring GAO Growth
Temperatures over 28 oC
Strong wastewater with low nitrogen content
Polysaccharides such as glucose are
dominant feed to anaerobic zone
Low pH in anaerobic zone
Anecdotal evidence suggests these may also
play a role
High SRT
Longer non-aerated zones
Periods of intermittent low organic loading
-
Some Filaments Accumulate P
Photo source: http://www.asissludge.com/NeisGram.htm
-
Neisser Stain
Reagents Used
Solution 1
Part A – Methylene Blue and Ethanol
Part B – Crystal Violet and Ethanol
Solution 2 – Bismark Brown
Tests for presence of polyphosphates stored
in cells
Critical to identify some filaments
Also shows PAOs
-
Neisser Staining Procedure
Fixation
Solution 1
Solution 2
Rinse
-
Neisser Stain Results
Negative Positive
Slightly brown or yellow –
very little stain adsorbed Grey-violet filaments
Blue-black globules in filaments
Colonies of blue-black cells Photo source: http://www.asissludge.com/NeisGram.htm
-
Oxygen in Anaerobic Zone
DO and nitrate will be used by
Heterotrophs
GAOs
PAOs
Reduces VFAs available for EBPR
Inhibits fermentation so fewer VFAs are
produced
Nothing good!
-
Avoid Introducing Oxygen
Into the Anaerobic Zone
Influent wastewater Cascading weirs
Screw pumps
Surface mixers
Bleed back from aerobic or anoxic zones Nitrate introduced by RAS
Solution: Baffles, curtains, submerged mixers,
covered tanks, etc.
Manage recycle streams
Maintain DO at 0.5 – 1.0 mg/L at end
of aerated zone
-
Recycle Streams
Anoxic Aerobic
An
ae
rob
ic
Internal Recycle
goes to anoxic
zone to protect
anaerobic zone.
RAS brings nitrate
and DO back to
anoxic zone
Keep DO
below 1 mg/L
leaving
aerated zone
Digester
supernatant
Centrate
Filtrate
-
Anaerobic zones as three compartments per ditch
Mixers to keep solids in suspension
Covered tanks
-
pH
Low pH can reduce and even prevent BPR
Maintain pH in aeration basin > 6.9
Maintain pH in anaerobic zone > 5.5
pH > 7.25 in anaerobic zone inhibits GAOs
48
-
Temperature
PAOs impaired above 28oC, GAOs favored
Can see decreased P removal below 15 oC
Reduced fermentation
Increased DO from influent and recycle streams
Washout
Might see better P removal below 15 oC because
GAOs can’t compete
Everything depends on rbCOD available
49
-
Hydraulic Retention Time
VFA uptake is rapid
HRT of 30 - 45 minutes or less usually sufficient
May be longer if fermentation is desired
Anaerobic zone SRT of 1 – 2 days
encourages fermentation
Equates to HRT of 1 – 2 hours
Anaerobic HRT may vary between 5 and 15
percent of the total nominal HRT of a full BNR
system
50
-
Modified University of
Cape Town or UCT
1st
Anoxic
2nd
Anoxic
An
ae
rob
ic
Aerobic
EBPR can be done by cycling from anaerobic to anoxic.
UCT protects anaerobic zone from excessive nitrate.
-
Solids Retention Time
EBPR has a washout SRT
Minimum system SRT of 3 to 4 days
Longer SRTs increase luxury uptake per cell
At very long SRTs, endogenous decay can cause secondary release and decreased performance
Stay under 30 days!
Because influent COD:P ratios vary, same SRT can give different results at different WWTPs
52
-
Secondary Release of Phosphorus
Source: EPA/600/R-10/100 August 2010
-
Causes of Secondary P Release
PAOs run out of critical storage item: PHA / PHB
Entering aerobic zone low on PHA/PHB: not enough energy for luxury uptake of P
Where do they run out?
Anaerobic zone when VFAs exhausted (too big)
Primary anoxic zone when nitrates exhausted
Secondary anoxic zone if no nitrates to be removed
Clarifier sludge blankets
Aerobic zone – too long – endogenous respiration begins
Phosphorus removal efficiency decreases
PAOs Must Cycle Between Anaerobic
and Aerobic/Anoxic Zones
55
PHB
Poly-P
Volatile Fatty Acids
Phosphate
Energy
PHB
Poly-P
Phosphate
Oxygen
Carbon Dioxide +H2O
Energy
(Nitrate)
Glycogen
Glycogen
-
Causes of Secondary P Release
Exposure to anaerobic conditions
Clarifier sludge blanket
Gravity Thickeners
Anaerobic Digester
Minimize clarifier blankets
-
Two FREE Manuals
Visit the EPA NEPIS website
EPA Design Manual for Phosphorus
Removal (1987) EPA/625/1-
87/001for detailed examples of
calculations
EPA Nutrient Control Design Manual
(2010) EPA/600/R-10/100
Download a copy of this
presentation. Password is
2017OhioWEAInd
Try our on-line training classes.
Approved for TU’s in Ohio.
Chemical
Phosphorus
Removal
59
-
Chemical Precipitation
Removes orthophosphate fraction of influent P
using chemistry
Poly-P is converted to orthophosphate during
biological treatment
React P with a metal salt OR lime
Can be used with or without biological
phosphorus removal
60
-
Phosphorus Fractionation
Phosphate
Polyphosphate
Organic
Phosphorus
~50%
Soluble
Ortho-P ~37%
Soluble
Poly-P
~12.5%
Organic
Note: Organic P may
be particulate or
soluble, biodegradable
or not.
-
Phosphorus Fractionation
Phosphate
Polyphosphate
Organic
Phosphorus
~4 mg/L
Soluble
Ortho-P ~3 mg/L
Soluble
Poly-P
~1 mg/L
Organic
-
Common Chemicals Used for
Phosphorus Removal
63
Chemical Formula Typical Weight Percent
in Commercial
Solutions
Aluminum sulfate (Alum) Al2(SO4)3●14(H2O) 48%
Sodium aluminate Na2Al2O4 20%
Polyaluminum chloride
(PAC)
Al12Cl12(OH)24 51%
Ferric chloride FeCl3 37 – 47%
Pickle liquor (Ferrous
sulfate or ferrous iron)
Fe2SO4 or Fe2+ Varies
Lime CaO, Ca(OH)2 NA
Source: Nutrient Control Design Manual, August 2010, EPA/600/R-10/100
-
Basic Chemistry
Al2(SO4)3●14H2O + 2H3(PO4)
2Al(PO4) + 3H2SO4 + 18H2O
2FeCl3●(6H2O) + 2H2PO4 + 2HCO3
2FePO4 + 3Cl2 + 2CO2 + 9H2O
64
Highest removal efficiency is between pH 5.5 and 7.0
Removal efficiency declines above pH 7
-
Medose/Pini Ratio
Medose is moles of metal added
Pini is the moles of soluble P in the
influent
-
What is a Mole?
6.022 * 1023 atoms (or molecules) in one mole
-
Basic Chemistry
Al2(SO4)3●14H2O + 2H3(PO4)
2Al(PO4) + 3H2SO4 + 18H2O
2FeCl3●(6H2O) + 2H2PO4 + 2HCO3
2FePO4 + 3Cl2 + 2CO2 + 9H2O
67
Highest removal efficiency is between pH 5.5 and 7.0
Removal efficiency declines above pH 7
-
Let’s Simplify for Aluminum
Al+3 + PO4-3 = AlPO4(s)
27 g/mole 31 g/mole
𝑅𝑎𝑡𝑖𝑜 = 27 𝑔 𝐴𝑙/𝑚𝑜𝑙𝑒
31 𝑔 𝑃/𝑚𝑜𝑙𝑒= 0.87
-
Let’s Simplify for Iron
Fe+3 + PO4-3 = FePO4(s)
55.8 g/mole 31 g/mole
𝑅𝑎𝑡𝑖𝑜 = 55.8 𝑔 𝐹𝑒/𝑚𝑜𝑙𝑒
31.0 𝑔 𝑃/𝑚𝑜𝑙𝑒= 1.8
-
Medose/Pini Ratio
Mole ratio holds true when effluent P is greater than 1 mg/L.
Stoichiometric doses Ferric dose of 1.8 g Fe per g P
Alum dose of 0.87 g Al per g P
Medose/Pini Ratios of 1.5 to 2.0 are needed to remove 80 – 98% of soluble P
Medose/Pini Ratios of 6 to 7 are needed to get below 0.10 mg/L.
Side reactions!
-
P Removal with Ferric Chloride
"stoichiometric"1 precipitate
2 precipitates
“equilibrium”
-
What is Going On?
Competing reactions
FePO4(s) Fe3+ + PO43-
Fe(OH)3(s) Fe3+ + 3OH-
-
Reactions of Lime with P
When lime is added to water, it reacts to
form calcium carbonate – CaCO3
At pH > 10, excess calcium reacts with
phosphate to form hydroxylapatite
73
5Ca2+ + 4OH- + 3HPO4- Ca5OH(PO4)3 + 3H2O
-
Solubility curves for AlPO4(s), FePO4(s)
and Ca-phosphate solids
Ca phosphates
FePO4
AlPO4
-
Other Factors Besides Dose
Wastewater characteristics
Method of chemical addition
Chemical addition feeding point(s)
Reaction pH
Flocculation method
Time
-
Biological Solids are Always
Leaving the System
When solids leave the system, other things
leave too
BOD
TKN
Phosphorus
Remember the ratios? 12% N and 2% P
So… is it possible to meet a 0.05 mg/L P
standard when effluent TSS is 12 mg/L?
76
(12 mg/L)(0.02) = 0.24 mg/L P
-
Solids Separation Key to
Phosphorus Removal
Sedimentation in Secondary Clarifier
Tertiary filtration
Achieves effluent P < 0.5. mg/L
Traditional media filters
Upflow continuous backwash filters
Cloth media filters
Membranes
Other proprietary processes
77
-
Effect on Sludge Production
Treatment Location
Increase in Sludge Production
Process Total
Metal salts to primary clarifier 50 – 100% 60 – 70% Metal salts to secondary
treatment to achieve effluent P
in the range of 0.5 – 1.0 mg/L
35 to 45% 5 – 25%
Tertiary application of metal
salts to achieve effluent P less
than 0.1 mg/L
45 to 60% 10 to 40%
78
Lime precipitation produces greater volumes of sludge
because of lime’s reaction with natural alkalinity.
-
Operational Impacts
Added upstream of secondary process
May remove too much BOD
Increases inert fraction in aeration basin
Improves sludge settleability
Potential for nutrient limitations downstream
Added after secondary clarifier
Enhances colloidal nitrogen removal
Filter backwash contains unreacted chemical
which is recycled to headworks or aeration basin
-
Two FREE Manuals
Visit the EPA NEPIS website
EPA Design Manual for Phosphorus
Removal (1987) EPA/625/1-
87/001for detailed examples of
calculations
EPA Nutrient Control Design Manual
(2010) EPA/600/R-10/100
-
Blue PRO
Chemical addition with moving-bed filtration
Combines co-precipitation and adsorption
Uses hydrous ferric oxide-coated sand media
Media is continuously regenerated
Continuous backwashing
Demonstrated Total P levels of 0.009 – 0.06 ug/L
Also effective at removing heavy metals
-
Blue Pro System
-
Blue PRO
Vendor says: Blue PRO® installations are
meeting permit limits as low as 0.05 mg/L
with a chemical dose of only 10 mg/L as Fe.
Georgetown, CO – 0.88 mgd
Plummer, ID – 0.35 mgd
Shintech, LA – 1.0 mgd
Broadway, VA – 3.5 mgd
-
Blue PRO Costs from EPA
Approx. Capital Cost 1 MGD $178,300
** Feb 2008 3 MGD $494,000 uninstalled
Approx. O&M Cost 1 MGD $29.830 annually
** Feb 2008 3 MGD $84,000 annually
Download a copy of this
presentation. Password is
2017OhioWEAInd
Try our on-line training classes.
Approved for TU’s in Ohio.