Transcript Document

CHAPTER 22
WASTEWATER MICROBIOLOGY
Unless otherwise noted, the following slides were
excerpted with permission from the following
presentation:
Nutrient Removal
How Low Can We Go?
Allen Gelderloos
Malcolm Pirnie, Inc.
Michigan Water Environment Association
June 2007
Presentation Outline
• Biological nitrogen removal
• Biological phosphorus removal
Biological nitrogen removal
Fundamental Nitrogen Cycle
Nitrogen Removal
Organic Matter
PROTEINS
CARBOHYDRATES
FATS
PROTEINS
Decomposition/
Hydrolysis
O2
NITROGEN
GAS
Cell Synthesis
AMMONIA
BIOMASS
Cell Lysis
Nitrification
O2
Organic
Carbon
NITRITE
NITRATE
NO3- + org-C + 0.2H2CO3  Cells + 0.5N2 + HCO3- + 1.5H2O
Inorganic
Carbon
NH4+ + 2O2 + 2HCO3-  Cells + 2H2CO3 + NO3- + H2O
Fate of Influent Nitrogen
Org-N
Ammonification
Org-N
NH4-N
Cells
Influent
Total
Kjeldahl
Nitrogen
(TKN)
NH4-N
Nitrification
NH4-N
NO3-N
Aerobic
Nitrogen Gas
Denitrification
NO3-N
N2
Anoxic
Nitrosomonas
Nitrobacter
Heterotrophs
Components of Effluent
Total Nitrogen (TN)
Ammonia-N
0.1 – 1.0 mg/L
Achieving low TN means:
Nitrate - N
TN
Part. Org. N
0.5 – 1.5 mg/L
1.0 mg/L (Clarifiers)
0.5 mg/L (Filters)
0.01 mg/L (Membranes)
• Effective nitrification
• Effective denitrification
• Effective TSS removal
• Reduce rDON – But how?
Refractory
Dissolved
Org-N
1.0 - 1.5 mg/L
rDON is the focus of research to better understand
its sources, fate, and removal mechanisms.
Biological phosphorus removal
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)
Fundamental Biochemical Mechanisms
for Anaerobic Phase of EBPR
VFA
CH3COOH
CH3COOH
Poly-Pn
CH3COO- + H+
Acetate……..C2
Propionate…C3
Butyrate…….C4
Other………..>C4
Phosphorus
release
Poly-Pn-1
PAO
Cell
ATP
NOx
ADP
acetyl CoA
DO
TCA
M+
H+
M+
H+
NADH
H2PO4-
+ (e-)
NAD+
H2PO4-
P-release
OH-
H+
OH-
PHBn
PHBn+1
Carbon storage
Wentzel, et al. (1991)
Anaerobic Phase
Courtesy of Dr. Art Umble, Greeley & Hansen
Fundamental Biochemical Mechanisms
presence of
Aerobic Phase of EBPR The
VFA is essential
O2
CO2 + H2O
for Bio-P to be
successful.
Puptake > 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.
Poly-Pn
Synthesis
NADH
ATP
H+
+ (e-)
P-uptake
NAD+
H+ + (e-)
Poly-Pn-1
ADP
Electron
Transfer
For Bio-P removal
systems, a ratio of
VFA : Psol removed
of at least 8:1 is
optimal.
TCA
acetyl CoA
M+
M+
H+
H+
H2PO4-
H+ + (e-)
H2PO4-
NADH
NAD+
P-uptake
OH-
Wentzel, et al. (1991)
Jeyanayagam (2005)
Bouza et. al (2000)
PAO
Cell
OH-
PHBn
PHBn+1
Carbon consumption
Aerobic Phase
Courtesy of Dr. Art Umble, Greeley & Hansen
Fate of Phosphorus During Treatment
In Bioreactor
Influent
TP
Sol. P
(Ortho-P)
Following
Treatment
Biological
Transformation
Particulate
P
Process
Sol. P
(Ortho-P)
EBPR or
Chem
P Removal
Sol. P
Particulate
P
Particulate
P
Mechanism
Component Removed
Biological P Uptake
Soluble P
Chemical P
Removal
Chemical precipitation
Soluble P
Coagulation,
Flocculation
Particulate P
Solids Capture
Clarification, Filtration
Particulate P
EBPR
Effl.
TP
Sludge
Courtesy of Edmund Kobylinski Black & Veatch and Michigan Water Environment Association (MWEA)
The Essence of the Enhanced Biological
Phosphorus Removal Mechanism
Rapidly
Biodegradable
Substrate (VFAs)
CO2 + H2O
P Release
O2
or NO3
Energy
Energy
PHB
PHB
Polyphosphate
Excess
P Uptake
Polyphosphate
Cell
Synthesis
Anaerobic Zone
PHB = polyhdroxybutyrate
Aerobic or Anoxic Zone
The Essence of the EBPR Mechanism
Driving Force for P Release
• High stored P
Driving Force for P Uptake
• High VFAs in bulk solution
• High stored PHB
• High soluble P in solution
Anaerobic
Feed condition
or
Battery charging
Aerobic
Starved condition
or
Battery discharging
Waste Sludge
Loaded with P
VFA = volatile fatty acids
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)
Anaerobic
PAOs
• VFA uptake &
PHB storage
Aerobic
• Excess P Uptake
• PHB metabolized
• P Release
GAOs
• VFA uptake &
PHB storage
• Glycogen storage
• PHB metabolized
• Glycogen used
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
Phosphorus
Accumulating
Organism
C2 – C3
Glycogen
Accumulating
Organism
acetate
(50% - 60%)
propionate
(25% - 30%)
C4 – C6
butyrate
(5% - 15%)
other SCFA
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
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
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
5. Reactor Type
Plug flow produces more short-chain VFA
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)
SRTf < 10d and 20oC results in conversion of 15%-30% of sCOD to VFA;
Skalsky and Daigger (1995)
YAVE ≈ 0.08 mg VFA/mg VS
Courtesy of Dr. Art Umble, Greeley & Hansen
Filipe, et al (2001)
Bouzas, et al (2001)
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
Five Prerequisites for Reliable EBPR
2.
3.
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
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
The Essence of Critical Environments for
Biological Nutrient Removal
N2
CO2
Phosphorus
Nitrogen
Anoxic
Anaerobic
Aerobic
Dentrification
Pi - Release
Pi – Uptake
DO ~ 0.0 mg/L
NO3 > 1 mg/L
DO ~ 0.0 mg/L
NO3 ~ 0.0 mg/L
DO > 2.0 mg/L
NO3 > 10 mg/L
Readily Biodegradable
Carbon Substrate
Readily Biodegradable
Carbon Substrate
Courtesy of Dr. Art Umble, Greeley & Hansen
Soluble and
Particulate
Organic & Inorganic
Carbon Substrates
WAS