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Phosphorus

Removal

Sidney Innerebner, PhD, PE CWP

Indigo Water Group

Littleton, Colorado

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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

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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

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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)

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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.

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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

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Collection System Odor Control

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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

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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

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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

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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

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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

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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

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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.