biofilm in the water environment field · 2014-09-11 · •biofilms are unique microbial systems...
TRANSCRIPT
Biofilm in the Water Environment FieldFUNDAMENTALS, APPLICATION, AND FUTURE NEEDS
Leon Downing, Ph.D.
Freese and Nichols, Inc.
September 23, 2009
Outline
• What is a biofilm?
• Past applications
• Current applications
• Future needs
What is a biofilm?
• “cells immobilized at a substratum and frequently embedded in an organic polymer matrix [EPS] of microbial origin” - Characklis and Marshall 1990
What is a biofilm?
• Why is this important?
What is a biofilm?
• Cell residence time independent of hydraulic residence time
• Increased volumetric activity
• Increased operational stability
• Inherent ease in biomass:fluid separation
• Increased resistance to toxic/inhibitory shock loads
• Different bioconversion processes in the same reactor
What is a biofilm?
• Redox conditions
– Different environmental conditions for different metabolisms
– Ecological redox sequence
ORP (mV)
Electron Acceptor Condition
+300
+200
+100
0
-100
-200
-300
-400
Aerobic
Anoxic
FermentiveAnaerobic
O2
NO3-
SO42-
Carbon -Organics
What is a biofilm?
• Nitrogen removal
• Nitrification
• Denitrification
NH4+
N2
+2e-
DB
NO2-
NO2-
NO3-
ORP (mV)
Electron Acceptor Condition
+300
+200
+100
0
-100
-200
-300
-400
Aerobic
Anoxic
FermentiveAnaerobic
O2
NO3-
SO42-
Carbon -Organics
Simplified Nitrogen Cycle
What is a biofilm?
• Suspended growth
– Homogeneous conditions
• Biofilms
– Diffusion
– Different environments in same reactor
– Stratification of ecology• Heterotrophs (carbon oxidizers)
• Nitrifiers (ammonia oxidizers)
S
NH4+
Bulk Liquid Biofilm
NO3-
DO
BOD
Sub
stra
tum
Het
ero
tro
ph
s
Nit
rifi
ers
Het
ero
tro
ph
s
Past Applications
• Oldest applications in wastewater treatment
– Trickling filter (1890s)
– Attachment to walls observed to increase removal in activated sludge (1960s)
• Aerobic processes
• Low-tech, easy to operate
Current Applications
• Focus on design to take advantage of biofilm properties
• Main focus on nutrients
– Nitrogen
• Multiple commercial biofilm technologies
• Water environment field
– Wastewater treatment• IFAS, floc dynamics
– Headwater streams• Dentrification
Current Applications
• Integrated Fixed Film Activated Sludge (IFAS)– Hybrid treatment system that combines fixed film technology
with conventional activated sludge
Current Applications
• IFAS
– First application – 1943
– Gained momentum in late 1990s
– Main driver: increased nitrification in same tank volume
Current Applications
• IFAS
– Twist on impact of diffusion
– BOD is consumed in liquid
– Nitrifying biofilm
– Greatly increases nitrification per volume
DO
NH4+
Bulk Liquid Biofilm
NO3-
BOD
Sub
stra
tum
Current Applications
The Colony, Texas
Current Applications
Current Applications
0
5
10
15
20
25
30
35
40
Jan-0
5
Apr-
05
Jul-
05
Oct
-05
Jan-0
6
Apr-
06
Jul-
06
Oct
-06
Jan-0
7
Apr-
07
Jul-
07
Oct
-07
Jan-0
8
Apr-
08
Jul-
08
Oct
-08
Jan-0
9
Month
EF
FL
UE
NT
(m
gN
/L)
7 per. Mov. Avg. (Effluent)
Current Applications
Contact Stabilization Shut down IFAS Online
Downing et al. (2009) WEFTEC
Current Applications
Sludge
Holding Tank
Anoxic/Anaerobic
Zone
Anaerobic
Zone
Aerobic Zone
-25
-20
-15
-10
-5
0
Ch
ang
e in
Nit
rog
en (
mg
N/L
)
Anaerobic-1-B Anaerobic-2-B Aerobic-B
Downing et al. (2009) WEFTEC
Current Applications
• Diffusion in biofilm
– Aerobic and anoxic conditions
• The Colony
– Approx. 30% of denitrification in aerobic sections
– IFAS units
– 1-2 mm biofilms
DO
NH4+
Bulk Liquid Biofilm
NO3-
BOD
Sub
stra
tum
Current Applications
• What about a floc/granule?
– Floc-aggregate of bacteria
– Granule-big floc
– Are they biofilms??Diffusion gradients
EPS matrix
Immobilized cells
Substratum???
Dos Santos et al. (1996) Water Research
Current Applications
• Trinity River Authority (TRA) of Texas Central Region Wastewater System (CRWS) Treatment Plant
– 189 MGD plant
– Aerobic treatment
• Nutrient removal study using Biowin
Current Applications
• Nitrogen balance
– Influent TKN: 32 mgN/L
– Effluent NH3 + NO3-: 13 mgN/L
– Change in nitrogen: 19 mgN/L
– Where is the nitrogen going?• Assimilation: 12.5% of biomass (~3 to 5 mgN/L)
• Nitrogen removed: 14 to 15 mgN/L
FlowAeration Basins
Clarifiers
Current Applications
• Simultaneous nitrification and denitrification
– Nitrate reductase activated in sludge blanket
– High mixed liqour suspended solids (MLSS) concentration
– Leads to large flocs
~1mm
DO
NH4+
Bulk Liquid Biofilm
NO3-
BOD
Sub
stra
tum
DO
NH4+
NO3-
BOD
Biofilm Bulk Liquid
Current Applications
• Simultaneous nitrification and denitrification
– SND Switch in Biowin
– Means for accounting for SND• Floc diameter
• Nitrate reductase activity
0
2
4
6
8
10
12
14
16
18
0 0.1 0.2 0.3 0.4 0.5 0.6
SND "Switch" (mgO2/L)
Eff
luen
t N
itra
te (
mgN
/L)
Current Applications
• Headwater streams
– Nitrate from agriculture
– Some denitrification occurs in streams
– Limited by:• Oxygen
• Electron donor availability
Current Applications
• Denitrification with elemental sulfur
– Sulfur can serve as an electron donor for autotrophic denitrification
– Sulfur is solubilized by sulfur oxidizing bacteria in biofilms
– Sulfur diffuses through the biofilm• Used by both aerobic and anoxic metabolisms
DOBulk Liquid
Biofilm/Sediment
NO3-
Sulfur Bed
So SO42-
Current Applications
• Initial results
– Thin biofilms on sulfur particles (10-50 m)
– Denitrification rates 5 to 35 times as high as baseline rates• 0.5 gN/m2-day
– Significant sulfate production
Read-Daily et al. (submitted) Water Research
Future Needs
• New “environments”
• Modeling
• GHG production
Future Needs
• Membrane aerated biofilms (MABs)
– Co-diffusion biofilms• Solid substratum
• All substrate from bulk liquid
– Counter-diffusion biofilms• Porous substratum
• Delivery of oxygen from substratum
• Other substrates from bulk liquid
DO
NH4+
Bulk Liquid Biofilm
NO3-
BOD
Sub
stra
tum
DO
NO3-
Future Needs
• Hybrid Membrane Biofilm Process (HMBP)
– Similar to IFAS
– Attachment in Activated Sludge Process
– Bench-scale tests:• Aerobic biofilm, anoxic bulk liquid resulted in high total nitrogen (TN)
removal (Downing and Nerenberg, 2007)
• Ecology: nitrifiers in attachment, heterotrophs in suspension (Downing and Nerenberg, 2008a, 2008b)
– Pilot-scale testing to determine scale-up
Future Needs
• Hybrid Membrane Biofilm Process (HMBP)
– Pilot testing in conjunction with Metcalf&Eddy/AECOM
– Varied loading over 8 months
Downing et al. (2009) Water Environment Research
0
5
10
15
20
25
30
35
40
45
50
1 28 56 82 100 114 126 139 152 167 181 201 215 232
Day
Conce
ntr
atio
n (
mgN
/L)
NOx Effluent Ammonia Nitrogen Removed
A DCB
Future Needs
• Similar nitrification rates as IFAS
• High levels of denitrification
0
5
10
15
20
25
30
0.29 0.33 0.5 0.94
Nitrogen Loading (g m-2
day-1
)
Co
nce
ntr
atio
n (
gN
m-3
)
Influent TN
Effluent Ammonia
Effluent TN
Downing et al. (2009) Water Environment Research
Future Needs
• Modeling
– Mass transfer
– Biological consumption
– Biofilm structure
– Microbial competition
– Complexity vs. applicability
Boltz et al. (2009) Water Environment Research
Future Needs
• Greenhouse Gas (GHG) Emissions
– Nitrous oxide emissions during nitrification
– EPA has already set preliminary emissions values for WWTP
– Ratio of / max has been shown to be key to this production (Ahn et al., 2009)
NH4+
N2
+2e-
DB
NO2-
NO2-
NO3-
N2O
Future Needs
• GHG emissions controls
– max is the maximum growth rate for bacterial strain
– is the actual growth rate
Temperature Substrate Acceptor pH
Future Needs
• GHG production during nitrification
DO
NH4+
Bulk Liquid Biofilm
NO3-
BOD
Sub
stra
tum
Future Needs
• GHG production in IFAS units
– Joint project between SMU (Prof. Jim Yu) and FNI
– Compare liquid N2O concentration
– Floating carriers (BioPortz)
– Rope media (BioWeb)
Environmental Microbiology LabSouthern Methodist University
Future Needs
• Fundamental biofilm research
– Nerenberg lab at UND
– Microsensors and FISH
Summary
• Biofilms are unique microbial systems
– Physical, physiologically, and environmentally
• Application of biofilms has been around a long time
– First applications in 1890s
• Biofilms are here to stay
– One of the hottest topics in the water environment field
• Questions still remain…
Questions?
Current Applications
• Clarifiers
– Sludge blanket denitrification
– 4-6 mgN/L removed