Biological Nutrient Removal (BNR) Operation in Wastewater Treatment Plants
WASTEWATER MICROBIOLOGY for NUTRIENT REMOVAL
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Transcript of 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
Courtesy of Dr. Art Umble, Greeley & Hansen
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
Courtesy of Dr. Art Umble, Greeley & Hansen
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 Dr. Art Umble, Greeley & Hansen
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
Courtesy of Dr. Art Umble, Greeley & Hansen
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
Five Prerequisites for Reliable EBPR
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
Five Prerequisites for Reliable EBPR
5. Avoid secondary release
– Proper sizing of zones
• Oversizing could cause secondary P release
– Minimize/manage recycle P loads from sludge operations
Five Prerequisites for Reliable EBPR
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
Courtesy of Dr. Art Umble, Greeley & Hansen