JTAC Presentation – May 18, 2017

Nutrient Removal 101 -Process Fundamentals and

Operation

JTAC Presentation – May 18, 2017

Nutrient Removal 101 -Process Fundamentals and

Operation

Steve Polson, P.E.Steve Polson, P.E.

Presentation GoalsPresentation Goals

• Develop understanding of:– Why to remove nutrients– How to remove nutrients using biological

processes– Reasons for facilities configuration

• This is a presentation on basics

• Develop understanding of:– Why to remove nutrients– How to remove nutrients using biological

processes– Reasons for facilities configuration

• This is a presentation on basics

What are Nutrients?What are Nutrients?

• Inorganic constituents in wastewater that can cause problems when discharged

• Fortunately, they are also elements and compounds that micro-organisms can utilize, and in the process, remove from the wastewater

• Inorganic constituents in wastewater that can cause problems when discharged

• Fortunately, they are also elements and compounds that micro-organisms can utilize, and in the process, remove from the wastewater

Nutrients of Concern in WastewaterNutrients of Concern in Wastewater• Nitrogen

– Ammonia (NH3)– Nitrate (NO3

-)– Organic nitrogen– Sources contributing to wastewater?

• Human waste• Industrial sources (refrigeration, pulp and paper, mining,

food processing and refining)

• Nitrogen– Ammonia (NH3)– Nitrate (NO3

-)– Organic nitrogen– Sources contributing to wastewater?

• Human waste• Industrial sources (refrigeration, pulp and paper, mining,

food processing and refining)

Nutrients of Concern in WastewaterNutrients of Concern in Wastewater• Phosphorus

– Dissolved & particulate– Chemical categorization

• Orthophosphate (soluble)• Condensed phosphate (complex)• Organic phosphates (complex)

– Total phosphorus (TP) is reported• Complex forms must be converted to orthophosphate for

measurement

– Sources contributing to wastewater?• Human waste• Food waste• Detergents and cleaners• Industrial sources (industrial cleaners, steel production, metal

finishing, food and beverage processing, pharmaceuticals, and fertilizer production)

• Phosphorus– Dissolved & particulate– Chemical categorization

• Orthophosphate (soluble)• Condensed phosphate (complex)• Organic phosphates (complex)

– Total phosphorus (TP) is reported• Complex forms must be converted to orthophosphate for

measurement

– Sources contributing to wastewater?• Human waste• Food waste• Detergents and cleaners• Industrial sources (industrial cleaners, steel production, metal

finishing, food and beverage processing, pharmaceuticals, and fertilizer production)

Nutrients of Concern in WastewaterNutrients of Concern in Wastewater

• Selenium– At normal wastewater pH ranges there are four

forms (oxidation states) of selenium:1. Selenate (Se+6): Very Soluble and difficult to precipitate2. Selenite (Se+4): Soluble and can co-precipitate with

iron3. Elemental Selenium (Se0): A solid precipitant4. Selenide (Se-2): Readily Precipitates

• Selenium– At normal wastewater pH ranges there are four

forms (oxidation states) of selenium:1. Selenate (Se+6): Very Soluble and difficult to precipitate2. Selenite (Se+4): Soluble and can co-precipitate with

iron3. Elemental Selenium (Se0): A solid precipitant4. Selenide (Se-2): Readily Precipitates

– Sources:• Discharges from coal‐fired power plants using

selenium‐rich coal• Effluent from oil refineries• Infiltration/Inflow (I/I)

– Sources:• Discharges from coal‐fired power plants using

selenium‐rich coal• Effluent from oil refineries• Infiltration/Inflow (I/I)

Why Include Nutrient Removal Capabilities?Why Include Nutrient Removal Capabilities?

• Ammonia– Toxicity; oxygen demand

• Nitrate– Groundwater contamination (blue baby syndrome); algae

growth; reduce operating costs

• Phosphorus– Eutrophication in lakes and reservoirs (algae growth)

• Selenium– Negative effects on the growth and survival of juvenile

fish– Birth deformities in the larval offspring of adult fish

• Ammonia– Toxicity; oxygen demand

• Nitrate– Groundwater contamination (blue baby syndrome); algae

growth; reduce operating costs

• Phosphorus– Eutrophication in lakes and reservoirs (algae growth)

• Selenium– Negative effects on the growth and survival of juvenile

fish– Birth deformities in the larval offspring of adult fish

NitrificationNitrification

Nitrification Biologically Transforms Ammonia to NitrateNitrification Biologically Transforms Ammonia to Nitrate

Organic NitrogenOrganic Nitrogen

Ammonia NitrogenAmmonia Nitrogen

Bacterial DecompositionBacterial Decomposition

Bacterial CellsBacterial Cells Net GrowthNet Growth

DecompositionDecomposition

Raw SewageRaw Sewage

Nitrite (NO2-)Nitrite (NO2-)

Nitrate (NO3-)Nitrate (NO3-)

O2O2

O2O2

NitrificationNitrification

Nitrification Converts Ammonia to Nitrate in Two StepsNitrification Converts Ammonia to Nitrate in Two Steps

Step 1: 2NH4+ + 3O2Step 1: 2NH4+ + 3O2 2NO2

- + 2H2O + 4H+ + Cells2NO2- + 2H2O + 4H+ + Cells“Nitrosomonas”“Nitrosomonas”

Step 2: 2NO2- + O2Step 2: 2NO2- + O2 2NO3

- + Cells2NO3- + Cells

“Nitrobacter”“Nitrobacter”

Nitrifiers are “autotrophic”:• Carbon dioxide carbon source• Oxidize ammonia for energy

Nitrifiers are “autotrophic”:• Carbon dioxide carbon source• Oxidize ammonia for energy

4H+ is acidic4H+ is acidic

For Each Gram of Ammonia Nitrified:For Each Gram of Ammonia Nitrified:

• 4.6 gm O2 required– Increases aeration requirements

• 7.2 gm alkalinity (as CaCO3) destroyed– Can cause drop in pH

• 4.6 gm O2 required– Increases aeration requirements

• 7.2 gm alkalinity (as CaCO3) destroyed– Can cause drop in pH

Nitrification Can Be Accomplished in Several WaysNitrification Can Be Accomplished in Several Ways

• Basic Process– Suspended growth (activated sludge)– Attached growth (BAF)

• Configuration– Combined with carbon oxidation– Separate stage (following carbon oxidation)

• Nitrifying TF

• Focus of presentation is on suspended growth

• Basic Process– Suspended growth (activated sludge)– Attached growth (BAF)

• Configuration– Combined with carbon oxidation– Separate stage (following carbon oxidation)

• Nitrifying TF

• Focus of presentation is on suspended growth

Primary Control Parameter is Sludge Age (SRT)Primary Control Parameter is Sludge Age (SRT)

• Activated sludge process• SRT and wastewater characteristics

determine MLSS concentration• SRT must accommodate growth rate

– Slower for nitrifiers• Nitrification SRT is sensitive to:

– Temperature– Dissolved oxygen (DO)– Mixed liquor pH

• Activated sludge process• SRT and wastewater characteristics

determine MLSS concentration• SRT must accommodate growth rate

– Slower for nitrifiers• Nitrification SRT is sensitive to:

– Temperature– Dissolved oxygen (DO)– Mixed liquor pH

Nitrifier Minimum Aerobic SRT Varies With Temperature.Nitrifier Minimum Aerobic SRT Varies With Temperature.

NitrificationNitrification

No NitrificationNo Nitrification

Assumes DO = 2.0 mg/LAssumes DO = 2.0 mg/L

Dissolved Oxygen Also Affects Minimum SRTDissolved Oxygen Also Affects Minimum SRT

• As DO decreases, min SRT increases– SRT at 0.3 mg/L double that at 2.0 mg/L

• DO in nitrifying system should be at least 2.0 mg/L

• However, DO above 3.0 mg/L is unnecessary and wastes energy

• As DO decreases, min SRT increases– SRT at 0.3 mg/L double that at 2.0 mg/L

• DO in nitrifying system should be at least 2.0 mg/L

• However, DO above 3.0 mg/L is unnecessary and wastes energy

Alkalinity Consumption Can Reduce Mixed Liquor pH Alkalinity Consumption Can Reduce Mixed Liquor pH

• Reduction in pH dependent on:– Alkalinity of raw wastewater– Extent of nitrification– Upstream processes (chemical addition,

denitrification)• ML pH less than 7.0 increases minimum

SRT for nitrification• Supplemental alkalinity may be needed

– Caustic soda (sodium hydroxide)– Soda ash (sodium bicarbonate)– Lime

• Reduction in pH dependent on:– Alkalinity of raw wastewater– Extent of nitrification– Upstream processes (chemical addition,

denitrification)• ML pH less than 7.0 increases minimum

SRT for nitrification• Supplemental alkalinity may be needed

– Caustic soda (sodium hydroxide)– Soda ash (sodium bicarbonate)– Lime

Operating SRT Must be Greaterthan Minimum SRTOperating SRT Must be Greaterthan Minimum SRT

• Accounts for fact that plant is not ideal reactor, diurnal variations

• Ratio of operating SRT to minimum is called “Operating Factor” (OF)– Also called “safety factor”

• OF is typically 1.5 to 2.5• Determined through experience

• Accounts for fact that plant is not ideal reactor, diurnal variations

• Ratio of operating SRT to minimum is called “Operating Factor” (OF)– Also called “safety factor”

• OF is typically 1.5 to 2.5• Determined through experience

Source : MWRD Robert W. Hite Treatment FacilitySource : MWRD Robert W. Hite Treatment Facility

Operating Factor Determines Effluent AmmoniaOperating Factor Determines Effluent Ammonia

SRT Based on Operating Factor is Aerobic SRTSRT Based on Operating Factor is Aerobic SRT

• Sludge mass under aerationAer SRT, days = (MLSS x Aer Vol x 8.34)/(Sludge Wasting Rate)

=(Aerobic Sludge Inventory, lb)/(Sludge Wasting Rate, lb/day)Note:• MLSS in mg/L• Aer Vol in mgal

• Sludge mass under aerationAer SRT, days = (MLSS x Aer Vol x 8.34)/(Sludge Wasting Rate)

=(Aerobic Sludge Inventory, lb)/(Sludge Wasting Rate, lb/day)Note:• MLSS in mg/L• Aer Vol in mgal

Aerobic SRT Can be Converted to Overall Operating SRTAerobic SRT Can be Converted to Overall Operating SRT

• SRT based on OF must be divided by percent of basin volume that is aerated for overall operating SRT

• SRT managed by sludge wasting (typical activated sludge control)

• Wasting rate (lb/day) = WAS flow (mgd) x Conc (mg/L) x 8.34; or

• WAS flow (mgd) = Wasting rate (lb/day)/[Conc (mg/L) x 8.34]

• SRT based on OF must be divided by percent of basin volume that is aerated for overall operating SRT

• SRT managed by sludge wasting (typical activated sludge control)

• Wasting rate (lb/day) = WAS flow (mgd) x Conc (mg/L) x 8.34; or

• WAS flow (mgd) = Wasting rate (lb/day)/[Conc (mg/L) x 8.34]

DenitrificationDenitrification

Denitrification Completes the Nitrogen Conversion ProcessDenitrification Completes the Nitrogen Conversion Process

Organic NitrogenOrganic Nitrogen

Ammonia NitrogenAmmonia Nitrogen

Bacterial DecompositionBacterial Decomposition

Bacterial CellsBacterial Cells Net GrowthNet Growth

DecompositionDecomposition

Raw SewageRaw Sewage

Nitrite (NO2-)Nitrite (NO2-)

Nitrate (NO3-)Nitrate (NO3-)

O2O2

O2O2

NitrificationNitrification

Nitrogen Gas (N2)Nitrogen Gas (N2)DenitrificationDenitrification

Org CarbonOrg Carbon

Nitrogen gas is harmless byproduct Nitrogen gas is harmless byproduct

Denitrification Converts Nitrate to Nitrogen Gas (cont)Denitrification Converts Nitrate to Nitrogen Gas (cont)

Denitrifiers are “facultative/heterotrophic”:• Oxygen obtained from dissolved oxygen or nitrate• Organic carbon serves as carbon source

Denitrifiers are “facultative/heterotrophic”:• Oxygen obtained from dissolved oxygen or nitrate• Organic carbon serves as carbon source

Denitrification occurs under “anoxic” conditions• Nitrate present• No dissolved oxygen

Denitrification occurs under “anoxic” conditions• Nitrate present• No dissolved oxygen

6NO3- + 5CH3OH6NO3- + 5CH3OH 3N2 + 5CO2 + 7H2O + 6OH-3N2 + 5CO2 + 7H2O + 6OH-

Typical reaction:Typical reaction:

OH- is basicOH- is basic

(methanol)

For Each Gram of Nitrate Denitrified:For Each Gram of Nitrate Denitrified:

• 2.9 gm BOD consumed– Reduces downstream aeration requirements

• 3.6 gm (as CaCO3) alkalinity produced– Partially offsets nitrification reduction

• 2.9 gm BOD consumed– Reduces downstream aeration requirements

• 3.6 gm (as CaCO3) alkalinity produced– Partially offsets nitrification reduction

Denitrification Efficiency Can Vary Denitrification Efficiency Can Vary

• Enhanced by wastewater biodegradability– Readily available food for denitrification

• Adversely affected by DO

• Enhanced by wastewater biodegradability– Readily available food for denitrification

• Adversely affected by DO

Denitrification Can Be Added in Several WaysDenitrification Can Be Added in Several Ways

• Basic Process– Suspended growth (activated sludge)– Attached growth

• Configuration– Combined with carbon oxidation/nitrification– Separate stage (following carbon

oxidation/nitrification)• Focus of presentation is on suspended

growth

• Basic Process– Suspended growth (activated sludge)– Attached growth

• Configuration– Combined with carbon oxidation/nitrification– Separate stage (following carbon

oxidation/nitrification)• Focus of presentation is on suspended

growth

Nitrification and Denitrification are Complimentary Reactions.Nitrification and Denitrification are Complimentary Reactions.

But, Denitrification Must Precede Nitrificationfor Benefit.

But, Denitrification Must Precede Nitrificationfor Benefit.

Typical Activated Sludge Process Configuration:Typical Activated Sludge Process Configuration:

RASRAS

PEPE

SESEOxicOxic

Carbon OxidationCarbon OxidationNitrificationNitrification

WASWAS

Secondary Clarifier

Secondary ClarifierActivated Sludge

ReactorActivated Sludge

Reactor

Two-Stage Activated Sludge Process Configuration for Denitrification:Two-Stage Activated Sludge Process Configuration for Denitrification:

RASRAS

PEPE

MLRMLR

SESEAnoxicAnoxic OxicOxic

DenitrificationDenitrification Carbon OxidationCarbon OxidationNitrificationNitrification

WASWAS

Secondary Clarifier

Secondary Clarifier

BNR ReactorBNR Reactor

Modified Ludzack-Ettinger (MLE) Process

Denitrification is Controlled by Mixed Liquor Recirculation.Denitrification is Controlled by Mixed Liquor Recirculation.

% Denite = R/(R+Q) * 100% Denite = R/(R+Q) * 100

4-Stage Activated Sludge Process Configuration for Denitrification:4-Stage Activated Sludge Process Configuration for Denitrification:

RASRAS

PEPE

MLRMLR

SESEAnoxicAnoxic OxicOxic

WASWAS

Secondary Clarifier

Secondary Clarifier

BNR ReactorBNR Reactor

AerobicAerobic AnoxicAnoxic

MethanolMethanol

Achieves Lower Effluent Nitrate ConcentrationsAchieves Lower Effluent Nitrate Concentrations

4-Stage Bardenpho Process

Deammonification Deammonification

• Sidestream Treatment– e.g., Centrate from anaerobic sludge dewatering

• Key organism – deammonification (annamox) bacteria• Two stage process

– Ammonia oxidizing bacteria (AOB) – half the available ammonia is oxidized to nitrite (nitritation, not nitrification)

– Annamox bacteria -- Residual ammonia combined with nitrite is anaerobicallytransformed to nitrogen gas.

• Sidestream Treatment– e.g., Centrate from anaerobic sludge dewatering

• Key organism – deammonification (annamox) bacteria• Two stage process

– Ammonia oxidizing bacteria (AOB) – half the available ammonia is oxidized to nitrite (nitritation, not nitrification)

– Annamox bacteria -- Residual ammonia combined with nitrite is anaerobicallytransformed to nitrogen gas.

(Source: Demon® literature)

Deammonification (cont) Deammonification (cont)

• Notable properties of anammox bacteria:– Very low growth rate (1/10th that of nitrifiers!)– Inhibited by oxygen even at very low levels

• Processes are proprietary• Can be difficult to control• Claims:

– 80+ percent ammonia removal– 60 percent less energy required– Eliminates need for supplemental carbon (methanol) for denitrification– 90 percent less sludge production

• Notable properties of anammox bacteria:– Very low growth rate (1/10th that of nitrifiers!)– Inhibited by oxygen even at very low levels

• Processes are proprietary• Can be difficult to control• Claims:

– 80+ percent ammonia removal– 60 percent less energy required– Eliminates need for supplemental carbon (methanol) for denitrification– 90 percent less sludge production

Annamox OrganismsAnnamox Organisms

Not a bad rash…

Deammonification Systems Deammonification Systems

Greeley has Demon® process (first in CO)

(Proprietary)

Biological Phosphorus

Removal(Bio-P)

Biological Phosphorus

Removal(Bio-P)

Phosphorus Removal May Be Biological and/or ChemicalPhosphorus Removal May Be Biological and/or Chemical

• Biological treatment– Incorporation into activated sludge cell mass;

settle/waste to remove• Chemical treatment

– Conversion from soluble to settleable particulate form; settle/waste and/or filter to remove

• Focus today is on biological

• Biological treatment– Incorporation into activated sludge cell mass;

settle/waste to remove• Chemical treatment

– Conversion from soluble to settleable particulate form; settle/waste and/or filter to remove

• Focus today is on biological

Biological Phosphorus Removal FundamentalsBiological Phosphorus Removal Fundamentals

• Standard primary/secondary treatment removes some phosphorus– Example – Influent TP = 5.0 mg/L:

• 1.0 mg/L removed in primary clarifiers– Particulate removal with primary sludge

• 1.0 mg/L removed in secondary clarifiers– Incorporation into activated sludge cell mass; waste from

system• 3.0 mg/L +/- remaining in secondary effluent

• Standard primary/secondary treatment removes some phosphorus– Example – Influent TP = 5.0 mg/L:

• 1.0 mg/L removed in primary clarifiers– Particulate removal with primary sludge

• 1.0 mg/L removed in secondary clarifiers– Incorporation into activated sludge cell mass; waste from

system• 3.0 mg/L +/- remaining in secondary effluent

• Bio-P treatment improves phosphorus uptake– Grow microorganisms that store P (Bio-P

organisms)– Improved removals:

• 5.0 mg/L influent TP• 1.0 mg/L removed in primary clarifiers• 3-3.5 mg/L removed in secondary clarifiers• 0.5-1.0 mg/L remaining in secondary effluent

• Bio-P treatment improves phosphorus uptake– Grow microorganisms that store P (Bio-P

organisms)– Improved removals:

• 5.0 mg/L influent TP• 1.0 mg/L removed in primary clarifiers• 3-3.5 mg/L removed in secondary clarifiers• 0.5-1.0 mg/L remaining in secondary effluent

Biological Phosphorus Removal Fundamentals (cont)Biological Phosphorus Removal Fundamentals (cont)

PAO’s Have Unique Anaerobic/ Aerobic MetabolismPAO’s Have Unique Anaerobic/ Aerobic Metabolism

Anaerobic Conditions

Aerobic Conditions

Acetate

PO4-3

Energy

PO4-3

Energy

CO2 + H2OO2

PAOs Grow Slow But Faster Than NitrifiersPAOs Grow Slow But Faster Than Nitrifiers

Nitrifiers

PAOs

Bio-P Requires Anaerobic/Aerobic Basins and ClarifiersBio-P Requires Anaerobic/Aerobic Basins and Clarifiers

• Anaerobic basin– Devoid of oxygen and nitrate– Fermentation breaks down complex organic

materials to volatile fatty acids (VFAs)• Acetic acid (vinegar)

– Bio-P organisms store VFAs and release phosphorus (provides energy)

• Anaerobic basin– Devoid of oxygen and nitrate– Fermentation breaks down complex organic

materials to volatile fatty acids (VFAs)• Acetic acid (vinegar)

– Bio-P organisms store VFAs and release phosphorus (provides energy)

• Aerobic basin– Basin contents aerated– Bio-P organisms oxidize stored VFAs and use

energy gained to store phosphorus• VFA oxidation provides energy for P-storage• Higher concentration in cells than typical • Most of soluble phosphorus removed

– Carbon oxidation, nitrification, and phosphorus uptake occur simultaneously

• P release and uptake simulates rechargeable battery– Stored P -- high energy bonds– Bugs break bonds and gains energy

• Aerobic basin– Basin contents aerated– Bio-P organisms oxidize stored VFAs and use

energy gained to store phosphorus• VFA oxidation provides energy for P-storage• Higher concentration in cells than typical • Most of soluble phosphorus removed

– Carbon oxidation, nitrification, and phosphorus uptake occur simultaneously

• P release and uptake simulates rechargeable battery– Stored P -- high energy bonds– Bugs break bonds and gains energy

Bio-P Requires Anaerobic/Aerobic Basins and Clarifiers (cont)Bio-P Requires Anaerobic/Aerobic Basins and Clarifiers (cont)

• Secondary Clarifiers– Activated sludge settles for recycle and

wasting (removes phosphorus)– Effluent phosphorus concentration dependent

on solids removal efficiency– “Secret” of bio-P removal – Remove the bugs

at the point where they have stored P (i.e., after aerobic treatment)

• Secondary Clarifiers– Activated sludge settles for recycle and

wasting (removes phosphorus)– Effluent phosphorus concentration dependent

on solids removal efficiency– “Secret” of bio-P removal – Remove the bugs

at the point where they have stored P (i.e., after aerobic treatment)

Bio-P Requires Anaerobic/Aerobic Basins and Clarifiers (cont)Bio-P Requires Anaerobic/Aerobic Basins and Clarifiers (cont)

Typical Process for Bio-P (and Nitrogen) Removal:Typical Process for Bio-P (and Nitrogen) Removal:

RASRAS

MLRMLR

SESE

DenitrificationDenitrification Carbon OxidationCarbon OxidationNitrificationNitrification

AnaerobicAnaerobic OxicOxicAnoxicAnoxic

Phosphorus UptakePhosphorus Uptake

Phosphorus Release

Phosphorus Release

WASWAS

PEPE

BNR ReactorBNR Reactor Secondary Clarifier

Secondary Clarifier

P-removalP-removal

A2O Process

Alternate Process for Bio-P (and Nitrogen) Removal:Alternate Process for Bio-P (and Nitrogen) Removal:

RASRAS

MLRMLR

SESEAnaAna OxicOxicAnxAnx

WASWAS

PEPE

BNR ReactorBNR Reactor Secondary Clarifier

Secondary Clarifier

P removalP removal

Johannesburg (JHB) Process

AnxAnx

Key: RAS ANX Zone

Bio-P Removal is Sensitive to Raw WW and System Operation Bio-P Removal is Sensitive to Raw WW and System Operation

• Readily degradable BOD• Recycle of DO and nitrate to anaerobic

zone• Excellent secondary clarifier

performance

• Readily degradable BOD• Recycle of DO and nitrate to anaerobic

zone• Excellent secondary clarifier

performance

How to Improve Bio-P Performance?How to Improve Bio-P Performance?

• Add supplemental carbon source– Acetic acid– High fructose corn syrup– Dairy waste– Brewery waste

• Create VFAs “in-house”– Primary sludge fermentation

• Hold sludge in separate fermenter• Often coupled with gravity thickening

• JHB process

• Add supplemental carbon source– Acetic acid– High fructose corn syrup– Dairy waste– Brewery waste

• Create VFAs “in-house”– Primary sludge fermentation

• Hold sludge in separate fermenter• Often coupled with gravity thickening

• JHB process

Bio-P Comes with a PriceBio-P Comes with a Price

• Struvite– Ammonium-magnesium-phosphate

(NH4MgPO4·6H2O)– Forms in solids processing– Creates problems with pipe plugging, damage

to pumps, centrifuges

• Struvite– Ammonium-magnesium-phosphate

(NH4MgPO4·6H2O)– Forms in solids processing– Creates problems with pipe plugging, damage

to pumps, centrifuges

Phosphorus RecoveryPhosphorus Recovery

• Sludge from EBPR plants is high in phosphorus and ammonia– Can cause struvite problems in digesters and piping

• Struvite is ammonium-magnesium-phosphate• Intentional creation of struvite results in high-P

fertilizer– Replaces mined phosphorus

• Limited resource

– Generates income

• Patented processes:– Ostara PearlTM

– Aquatec Maxon Crystalactor®

• Sludge from EBPR plants is high in phosphorus and ammonia– Can cause struvite problems in digesters and piping

• Struvite is ammonium-magnesium-phosphate• Intentional creation of struvite results in high-P

fertilizer– Replaces mined phosphorus

• Limited resource

– Generates income

• Patented processes:– Ostara PearlTM

– Aquatec Maxon Crystalactor®

AirPrex Piloting at MetroAirPrex Piloting at Metro

• Anaerobic digester effluent treated to form struvite– AirPrex reactor

• Strip CO2 to raise pH• Add magnesium to form

struvite• Struvite settles and is

removed from digested sludge prior to dewatering

• Anaerobic digester effluent treated to form struvite– AirPrex reactor

• Strip CO2 to raise pH• Add magnesium to form

struvite• Struvite settles and is

removed from digested sludge prior to dewatering

Struvite Product

Selenium – The Latest ChallengeSelenium – The Latest Challenge

• Effluent permits starting to limit selenium

• Why?– Negative effects on the growth and survival of

juvenile fish– Birth deformities in the larval offspring of adult

fish

• Effluent permits starting to limit selenium

• Why?– Negative effects on the growth and survival of

juvenile fish– Birth deformities in the larval offspring of adult

fish

Selenium ChemistrySelenium Chemistry

• At normal wastewater pH ranges there are four forms (oxidation states) of selenium:1. Selenate (Se+6): Very Soluble and difficult to

precipitate2. Selenite (Se+4): Soluble and can co-

precipitate with iron3. Elemental Selenium (Se0): A solid precipitant4. Selenide (Se-2): Readily Precipitates

• At normal wastewater pH ranges there are four forms (oxidation states) of selenium:1. Selenate (Se+6): Very Soluble and difficult to

precipitate2. Selenite (Se+4): Soluble and can co-

precipitate with iron3. Elemental Selenium (Se0): A solid precipitant4. Selenide (Se-2): Readily Precipitates

Addressing SeleniumAddressing Selenium

• Reduce I/I• Treatment

– Incorporate into other processes– Separate stage

• Reduce I/I• Treatment

– Incorporate into other processes– Separate stage

Treatment ConsiderationsTreatment Considerations

• Reduce Se to Se0(elemental)• Microorganisms have hierarchy of preferred

electron sources:– Oxygen O2 → H2

– Nitrate/nitrite NO3 → N2

– Selenate/Selenite Se+6 → Se+4 → Se0

– Sulfate SO4 → S-

– Methanogenesis CO2 → CH4

• Therefore anoxic and anaerobic conditions will reduce/precipitate selenium

• Reduce Se to Se0(elemental)• Microorganisms have hierarchy of preferred

electron sources:– Oxygen O2 → H2

– Nitrate/nitrite NO3 → N2

– Selenate/Selenite Se+6 → Se+4 → Se0

– Sulfate SO4 → S-

– Methanogenesis CO2 → CH4

• Therefore anoxic and anaerobic conditions will reduce/precipitate selenium

Selenium TreatmentSelenium Treatment

• Not well studied or documented• Biological and chemical options

– Ferric chloride can precipitate Se• Success depends on how reduced

– ANA/ANX zones in BNR systems• Potential to reduce oxidation state• Need to limit final OXIC zone

– Combine biological and chemical?

• Not well studied or documented• Biological and chemical options

– Ferric chloride can precipitate Se• Success depends on how reduced

– ANA/ANX zones in BNR systems• Potential to reduce oxidation state• Need to limit final OXIC zone

– Combine biological and chemical?

Selenium TreatmentSelenium Treatment

• More Exotic Approaches– Downflow Packed Granular Filtration Beds (GE

ABMet)– Wetlands– Reverse osmosis

• Watch for future developments

• More Exotic Approaches– Downflow Packed Granular Filtration Beds (GE

ABMet)– Wetlands– Reverse osmosis

• Watch for future developments

Questions?Questions?

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