WASTEWATER MICROBIOLOGY for NUTRIENT REMOVAL

WASTEWATER

MICROBIOLOGY

for

NUTRIENT REMOVAL

MWEA Process Seminar

5 NOV 2014

Mackenzie L. Davis

Nutrient Removal

How Low Can We Go?

Michigan Water Environment Association

June 2007

Allen Gelderloos

Malcolm Pirnie, Inc.

Unless otherwise noted, the following slides were

excerpted with permission from the following

presentation:

Presentation Outline

• Biological nitrogen removal

• Biological phosphorus removal

Biological Nitrogen Removal

O2

O2

Fundamental Nitrogen Cycle Nitrogen Removal

Decomposition/

Hydrolysis

Nitrification

NITROGEN

GAS

PROTEINS

NITRITE

NITRATE

BIOMASS AMMONIA Cell Lysis

Cell Synthesis

Organic Matter

PROTEINS CARBOHYDRATES FATS

Inorganic

Carbon

NH4+ + 2O2 + 2HCO3

- Cells + 2H2CO3 + NO3- + H2O NO3

- + org-C + 0.2H2CO3 Cells + 0.5N2 + HCO3- + 1.5H2O

Organic

Carbon

Courtesy of Dr. Art Umble, Greeley & Hansen

Fate of Influent Nitrogen

Ammonification

Org-N NH4-N

Nitrification

NH4-N NO3-N

Denitrification

NO3-N N2

Influent

Aerobic Anoxic

Nitrogen Gas

Total

Kjeldahl

Nitrogen

(TKN)

Org-N

NH4-N

Cells

Nitrosomonas

Nitrobacter Heterotrophs

such as

Pseudomonas

Components of Effluent

Total Nitrogen (TN)

Achieving low TN means:

• Effective nitrification

• Effective denitrification

• Effective TSS removal

• Reduce rDON – But how?

0.1 – 1.0 mg/L Ammonia-N

Nitrate - N

Refractory

Dissolved

Org-N

Part. Org. N

0.5 – 1.5 mg/L

1.0 - 1.5 mg/L

1.0 mg/L (Clarifiers)

0.5 mg/L (Filters)

0.01 mg/L (Membranes)

TN

rDON is the focus of research to better understand

its sources, fate, and removal mechanisms.

Biological Phosphorus Removal

Some Definitions

• Polyphosphates = molecularly dehydrated phosphates

• All polyphosphates gradually hydrolyze in water to an ortho (PO4) form

• Typically found as monohydrogenphosphate in wastewater (HPO4)

• ADP = adenosine diphosphate

• ATP = adenosine triphosphate

Some Definitions Continued

• ATP is an energy carrier

• ADP + H3PO4 ATP + H2O

• Energy is released to the cell via ATP and

ATP reverts to ADP

• VFA = volatile fatty acids

• ANOXIC = NO3

Phosphorus Removal Terminology

• Biological phosphorus removal is also called

– Bio-P

– Enhanced Biological Phosphorus removal (EBPR)

– BPR

– Luxury P removal

• Biological Phosphorus Removal is

– removal of P in excess of metabolic requirements

• Collective term for the Bio-P microorganisms: Phosphorus Accumulating Organisms (PAOs)

• Some PAOs: Acinetobacter; Arthrobacter; Aeromonas

• Collective term for competing microorganisms: Glycogen Accumulating Organisms (GAOs)

The Essence of the Enhanced Biological

Phosphorus Removal Mechanism

Anaerobic Zone Aerobic (O2)

or

Anoxic Zone (NO3)

Rapidly

Biodegradable

Substrate (VFAs)

PHB

Poly-

phosphate

P Release

Energy

PHB

Polyphosphate

CO2 + H2O

O2

or NO3

Cell

Synthesis

Energy Excess

P Uptake

PHB = polyhdroxybutyrate

The Essence of the EBPR Mechanism

Aerobic Anaerobic

Driving Force for P Release

• High stored P

• High VFAs in bulk solution

Waste Sludge

Loaded with P

Starved condition

or

Battery discharging

Feed condition

or

Battery charging

Driving Force for P Uptake

• High stored PHB

• High soluble P in solution

VFA = volatile fatty acids

PHB = polyhdroxybutyrate

CH3COOH

ATP

ADP

acetyl CoA

NADH

NAD+

TCA

H+

+ (e-)

Poly-Pn

Poly-Pn-1

Phosphorus

release

PHBn

Carbon storage

PHBn+1

Anaerobic Phase

PAO

Cell

H2PO4-

M+ M+

H2PO4-

OH- OH-

CH3COO- + H+

CH3COOH

VFA

P-release

Wentzel, et al. (1991)

NOx

DO

H+ H+

Fundamental Biochemical Mechanisms

for Anaerobic Phase of EBPR

Acetate……..C2

Propionate…C3

Butyrate…….C4

Other………..>C4


ATP

ADP

Poly-Pn

Poly-Pn-1

P-uptake

PHBn

Carbon consumption PHBn+1

Aerobic Phase

PAO

Cell

H2PO4-

M+ M+

H2PO4-

H+ H+

P-uptake

O2 CO2 + H2O

NADH

NAD+

H+ + (e-)

acetyl CoA

TCA

H+

+ (e-)

NADH

NAD+

H+ + (e-)

Synthesis

Wentzel, et al. (1991)

Jeyanayagam (2005)

Bouza et. al (2000)

24-36 times more

energy is released

by the PHB oxidation

in the aerobic phase

than is used to store

PHB in the anaerobic

phase.

Puptake > Prelease

The presence of

VFA is essential

for Bio-P to be

successful.

For Bio-P removal

systems, a ratio of

VFA : Psol removed

of at least 8:1 is

optimal.

OH- OH-

Electron

Transfer

Fundamental Biochemical Mechanisms

Aerobic Phase of EBPR


Fate of Phosphorus During Treatment

Sol. P

(Ortho-P)

Particulate

P

TP

Influent

Sol. P

(Ortho-P)

Particulate

P

In Bioreactor

Biological

Transformation

Sol. P

Particulate

P

Following

Treatment

Effl.

TP

Sludge

EBPR or

Chem

P Removal

Process Mechanism Component Removed

EBPR Biological P Uptake Soluble P

Chemical P

Removal

Chemical precipitation Soluble P

Coagulation,

Flocculation

Particulate P

Solids Capture Clarification, Filtration Particulate P

Courtesy of Edmund Kobylinski Black & Veatch and Michigan Water Environment Association (MWEA)

VFAs Play a Central Role in EBPR

• VFA = Food for PAOs

– VFA:P removed = 4:1 to 16:1

• But rapidly biodegradable COD (rbCOD) is a

better estimate of VFA formation potential

– rbCOD:P removed = 15:1 (minimum)

• Potential sources VFAs

– Fermentation in sewer system

– Fermentation in anaerobic zone of the

bioreactor

– Primary sludge fermentation

– Purchased VFAs (acetic & propionic acid)

Courtesy of Edmund Kobylnski, Black& Veatch and Michigan Water Environment Association (MWEA)

The Good (PAOs) and the Bad (Glycogen

Accumulating Organisms, GAOs)

Aerobic Anaerobic

• VFA uptake &

PHB storage

• P Release

• Excess P Uptake

• PHB metabolized PAOs

• VFA uptake &

PHB storage

• Glycogen used

• Glycogen storage

• PHB metabolized GAOs

GAOs will compete with PAOs for VFAs

Presence of adequate VFAs does not necessarily ensure reliable

EBPR. As noted in the following slides, the proportions of VFA

components and environmental factors play a significant role.

Preferential sCOD for Bio-P Efficiency

Glycogen

Accumulating

Organism

Phosphorus

Accumulating

Organism

acetate (50% - 60%)

propionate (25% - 30%)

butyrate (5% - 15%)

other SCFA

Fermentation promotes production of acetate

and propionate as primary by-products Zeng, et al (2006)

Bouzas, et al (2000)

C2 – C3

C4 – C6

Drives the

competitive

advantage

to PAOs


Courtesy of Edmund Kobylinski, Black & Veatch and Michigan Water Environment Association (MWEA)

Factors Influencing Fermentation: Enhanced Biological Phosphorus Removal

1. Temperature

Acid production rate at low temperatures (<10oC) is poor

Acid production at 20oC is 5 times the rate at 10oC

2. pH Generally unaffected for pH between 4.3 and 7.0; However,

bacteria that break down fatty acids are highly sensitive

and inhibited at pH < 6.5

Teichgraber (2000)

Skalsky and Daigger (1995)

Filipe, et al (2001)

Bouzas, et al (2001)

5. Reactor Type Plug flow produces more short-chain VFA

3. Solids Retention Time (SRT) in Fermenter

Higher production at longer SRTs up to ~ 6 d;

SRT < 6d minimizes conversion of VFA to CH4

4. Primary solids concentration Lower concentrations can result in higher production

for a given SRT

The need for a fermentation step depends on how much VFA is present in the

influent and the amount of mass of phosphorus and nitrogen to be removed;

SRTf < 10d and 20oC results in conversion of 15%-30% of sCOD to VFA;

YAVE ≈ 0.08 mg VFA/mg VS


Conditions Thought to Favor GAO

Dominance

• Warm temperatures

• Long SRT

• Anoxic and anaerobic HRTs too long

• Continued use of acetic acid

• pH significantly less than 7

GAOs are always present and waiting for the

right conditions to thrive

Courtesy of Edmund Kobylinski, Black & Veatch, J.L. Barnard, and Michigan Water Environment Association

(MWEA)

Courtesy of Edmund Kobylinski, Black & Veatch and Michigan Water Environment Association (MWEA)

Five Prerequisites for Reliable EBPR

1. Consistent and adequate supply of VFAs

– Variable supply of VFAs appear to stress the PAOs due to PHB depletion

– Delays EBPR recovery even when VFA supply becomes adequate

– Smaller plants most susceptible

– Wet weather flows & snow melts also cause low VFAs

– Recycle loads can impact VFA:TP ratio

2. Preserve integrity of the anaerobic zone

– Critical for P release – No P release, no PAO selection

– 1 mg NO3-N deprives COD for 0.7 mg P

– 1 mg DO deprives COD for 0.3 mg P

3. Maximize solids capture

– Solids = Particulate P

• Improve sludge settleabilty

• Optimize clarifier & filter operation

• Maximize thickening & dewatering solids capture


4. Aerobic zone design

– Staging

• Helps 1st order P uptake – more efficient P removal

– Proper air distribution:

• Have PHB & Have P in bulk liquid, Need DO!

• Provide adequate DO in the initial zone to support rapid P uptake.

• Taper aeration in the subsequent zones - smaller driving force (lower PHB & lower bulk P), lower P uptake rate


5. Avoid secondary release

– Proper sizing of zones

• Oversizing could cause secondary P release

– Minimize/manage recycle P loads from sludge operations


Anoxic

DO ~ 0.0 mg/L

NO3 > 1 mg/L

Dentrification

Readily Biodegradable

Carbon Substrate

Anaerobic

DO ~ 0.0 mg/L

NO3 ~ 0.0 mg/L

Pi - Release

Readily Biodegradable

Carbon Substrate

Aerobic

DO > 2.0 mg/L

NO3 > 10 mg/L

Pi – Uptake

N2

Soluble and

Particulate

Organic & Inorganic

Carbon Substrates

WAS

CO2

Nitrogen

Phosphorus

The Essence of Critical Environments for

Biological Nutrient Removal


Questions?

Contact

Dr. Mackenzie Davis

[email protected]

Documents

WASTEWATER MICROBIOLOGY for NUTRIENT REMOVAL