CHAPTER 22 WASTEWATER MICROBIOLOGY

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CHAPTER 22WASTEWATER MICROBIOLOGY
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Nutrient Removal How Low Can We Go?
Unless otherwise noted, the following slides were
excerpted with permission from the following
presentation

• Allen Gelderloos
• Malcolm Pirnie, Inc.

Michigan Water Environment Association June 2007
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Presentation Outline

• Biological nitrogen removal
• Biological phosphorus removal

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Biological nitrogen removal
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Fundamental Nitrogen CycleNitrogen Removal
PROTEINS
CARBOHYDRATES
FATS
Decomposition/ Hydrolysis
AMMONIA
Nitrification
NH4 2O2 2HCO3- ? Cells 2H2CO3 NO3-
H2O
NO3- org-C 0.2H2CO3 ? Cells 0.5N2 HCO3-
1.5H2O
Courtesy of Dr. Art Umble, Greeley Hansen
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Fate of Influent Nitrogen
Ammonification Org-N NH4-N
Org-N
Nitrogen Gas
Influent
Cells
Total Kjeldahl Nitrogen (TKN)
Denitrification NO3-N N2
Nitrification NH4-N NO3-N
NH4-N
Aerobic
Anoxic
Nitrosomonas
Heterotrophs
Nitrobacter
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Components of Effluent Total Nitrogen (TN)
0.1 1.0 mg/L

• Achieving low TN means
• Effective nitrification
• Effective denitrification
• Effective TSS removal
• Reduce rDON But how?

0.5 1.5 mg/L
TN
1.0 mg/L (Clarifiers) 0.5 mg/L
(Filters)0.01 mg/L (Membranes)
1.0 - 1.5 mg/L
rDON is the focus of research to better
understand its sources, fate, and removal
mechanisms.
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Biological phosphorus removal
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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)
• Collective term for the competing microorganisms
  Glycogen Accumulating Organisms (GAOs)

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Fundamental Biochemical Mechanismsfor Anaerobic
Phase of EBPR
PAO Cell
CH3COOH
Acetate..C2 PropionateC3 Butyrate.C4 Other
..gtC4
acetyl CoA
M
M
H2PO4-
H
H
H2PO4-
P-release
Anaerobic Phase
Wentzel, et al. (1991)
Courtesy of Dr. Art Umble, Greeley Hansen
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Fundamental Biochemical MechanismsAerobic Phase
of EBPR
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 81
is optimal.
Puptake gt Prelease
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.
Synthesis
Poly-Pn
ATP
P-uptake
Poly-Pn-1
ADP
Electron Transfer
M
M
H2PO4-
H
H
H2PO4-
P-uptake
PHBn
OH-
OH-
PHBn1
PAO Cell
Carbon consumption
Aerobic Phase
Wentzel, et al. (1991) Jeyanayagam (2005) Bouza
et. al (2000)
Courtesy of Dr. Art Umble, Greeley Hansen
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Fate of Phosphorus During Treatment
Influent
Sol. P(Ortho-P)
TP
ParticulateP
Process Mechanism Component Removed
EBPR Biological P Uptake Soluble P
Chemical P Removal Chemical precipitation Soluble P
Chemical P Removal Coagulation, Flocculation Particulate P
Solids Capture Clarification, Filtration Particulate P
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Courtesy of Edmund Kobylinski Black Veatch and
Michigan Water Environment Association (MWEA)
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The Essence of the Enhanced Biological
Phosphorus Removal Mechanism
RapidlyBiodegradable Substrate (VFAs)
CO2 H2O
O2 or NO3
P Release
Energy
ExcessP Uptake
Energy
PHB
PHB
Poly-phosphate
Polyphosphate
Cell Synthesis
Aerobic or Anoxic Zone
Anaerobic Zone
PHB polyhdroxybutyrate
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The Essence of the EBPR Mechanism

• Driving Force for P Release
• High stored P
• High VFAs in bulk solution

• Driving Force for P Uptake
• High stored PHB
• High soluble P in solution

Anaerobic
Aerobic
Starved conditionorBattery discharging
Feed conditionorBattery charging
Waste SludgeLoaded with P
VFA volatile fatty acids
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VFAs Play a Central Role in EBPR

• VFA Food for PAOs
• VFAP removed 41 to 161
• But rapidly biodegradable COD (rbCOD) is a better
  estimate of VFA formation potential
• rbCODP removed 151 (minimum)
• Potential sources VFAs
• Fermentation in sewer system
• Fermentation in anaerobic zone of the bioreactor
• Primary sludge fermentation
• Purchased VFAs (acetic propionic acid)

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Courtesy of Edmund Kobylnski, Black Veatch and
Michigan Water Environment Association (MWEA)
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The Good (PAOs) and the Bad (Glycogen
Accumulating Organisms, 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.
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Preferential sCOD for Bio-P Efficiency
Phosphorus Accumulating Organism
Glycogen Accumulating Organism
Drives the competitive advantage to PAOs
Fermentation promotes production of acetate and
propionate as primary by-products
Zeng, et al (2006) Bouzas, et al (2000)
Courtesy of Dr. Art Umble, Greeley Hansen
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Courtesy of Edmund Kobylinski, Black Veatch and
Michigan Water Environment Association (MWEA)
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• Factors Influencing Fermentation
• Enhanced Biological Phosphorus Removal

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
Teichgraber (2000) Skalsky and Daigger
(1995) Filipe, et al (2001) Bouzas, et al (2001)
SRTf lt 10d and 20oC results in conversion of
15-30 of sCOD to VFA
YAVE 0.08 mg VFA/mg VS
Courtesy of Dr. Art Umble, Greeley Hansen
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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
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Courtesy of Edmund Kobylinski, Black Veatch,
J.L. Barnard, and Michigan Water Environment
Association (MWEA)
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Courtesy of Edmund Kobylinski, Black Veatch and
Michigan Water Environment Association (MWEA)
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Five Prerequisites for Reliable EBPR

• 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 VFATP ratio

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Five Prerequisites for Reliable EBPR

• 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
• Maximize solids capture
• Solids Particulate P
• Improve sludge settleabilty
• Optimize clarifier filter operation
• Maximize thickening dewatering solids capture

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Five Prerequisites for Reliable EBPR

• 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

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Five Prerequisites for Reliable EBPR

• Avoid secondary release
• Proper sizing of zones
• Oversizing could cause secondary P release
• Minimize/manage recycle P loads from sludge
  operations

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The Essence of Critical Environments for
Biological Nutrient Removal
Phosphorus
Nitrogen
Anoxic DO 0.0 mg/L NO3 gt 1 mg/L
Anaerobic DO 0.0 mg/L NO3 0.0 mg/L
Dentrification
Pi - Release
Pi Uptake
Courtesy of Dr. Art Umble, Greeley Hansen