total nitrogen removal in the hybrid membrane-biofilm process
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Total Nitrogen Removal in the Hybrid Membrane-Biofilm Process
Robert NerenbergDepartment of Civil Engineering and Geosciences
University of Notre Dame
Metropolitan Water Reclamation District of Greater ChicagoAugust 22, 2008
2
Acknowledgements
Leon Downing Kyle BibbyCollaborators: K. Esposito, B. Bodniewicz, T. Fascianella (Metcalf & Eddy)
Funding:
5
“Classic” Eutrophication Examples
http://www.longislandsoundstudy.net/pubs/reports/sh03_p1.pdf
Long Island Sound
http://www.cbf.org/site/PageServer?pagename=resources_facts_deadzone
Chesapeake Bay
http://www.ncat.org/nutrients/hypoxia/hypoxia.html
Gulf of Mexico
6
1990 2000 2010
NH3 -N,TN,
mg/L
Year
2
4
6
8
10
0
Nitrogen Standards for Wastewater
Source: Art Umble, Ph.D., Greeley and Hansen
TN = total nitrogen
= NH4+ + NO3
- + NO2- + org N
7
Biological Nitrogen Removal
1) Nitrification
Ammonia oxidizing bacteria (AOB) (Nitrosomonas)
NH4+ + O2 NO2
-
Nitrite oxidizing bacteria (NOB) (Nitrobacter, Nitrospira)
NO2- + O2 NO3
-
8
Biological Nitrogen Removal
2) Denitrification
Heterotrophic denitrifying bacteria (DB)
BOD + NO3- (NO2
- ) N2
9
Conventional N removal
Biological Nitrogen Removal
NO2- NO3
-AOB NOB
NH4+
6e- 2e-
Nitrification
N2 3e- 2e-
DB DBNO2
-
Denitrification
10
N2 3e- 2e-
DB DBNO2
-
Shortcut Nitrogen Removal
NO2- NO3
-AOB NOB
Conventional N removal
Shortcut N removal
NH4+
6e- 2e-X
X
X
25% reduction in oxygen40% reduction in BOD Low DO favors AOB over NOB
11
Wastewater Treatment
BOD, NH4
+
O2
Settling
tank
Aeration
basin
Anoxic
basin
NO3-
NH4+
Need high SRT!
Aerobic nitrification (AOB/NOB)
Anoxic denitrification
NO3- NO3
-
12
Many older plants cannot achieve nitrification
• Short SRTs
• Landlocked
Upgrades: • Space• Capital costs• Energy
13
Biofilms can retain nitrifiers
IFAS, MBBRLimited denitrification
http://www.brentwoodhttp://www.brentwood--ind.com/water/ifas_main.htmlind.com/water/ifas_main.html
16
Membrane-Biofilm Reactors
281 μm
1 μm
Water
O2
O2
NH4+
Hydrophobic polymers
High specific surface area
Variable driving force J=K(CL-C)
Low energy consumption
17
Hollow-Fiber Membrane Biofilm Process (HMBP)
Return Activated Sludge
Settler Influent (BOD, NH4 +)
Hollow Fiber Membranes
Compressed air to membranes
• Nitrification with short SRTs
• Hybrid thinner biofilms
• Denitrification in bulk
• Passive aeration save up to 70% on energy
18
HMBP Conceptual Model
BODNH4
+
NH4+
O2
Hollow-fiber membrane
Biofilm
Bulk liquid
BOD
Heterotrophs
Settler
NO3-
NO2-
Dep
th
Concentration
AOB, NOB
NO2-
NO3-
DONO2
-
NO3-
NH4+
BOD
• Nitrifiers in biofilm (AOB/NOB)
• Heterotrophs in bulk
• Maximal use of influent BOD for denitrification
(Anoxic)
S is insensitive to BOD loading)1(
1
max xx
x
bqb
kSθθ
θ+−Υ
+=
)1()(
x
ox
a bSSXθθ
θ+−
Υ=
19
Research Objectives
1. Test HMBP concept2. Explore effects of membrane DO and
bulk BOD on nitrification rates3. Can the HMBP be scaled up?
22
Bench Scale HMBP
Return Activated Sludge
Settler Influent (BOD, NH4 +)
Hollow Fiber Membranes
Compressed air to membranes
23
Performance Tests
Test HMBP for a variety of NH4+ and
BOD loadings
Determine location and activity of AOB, NOB, and Heterotrophs
24
BOD=0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
2.2 (4.0) 4.0 (6.0) 5.0 (12.0) 7.5 (17.0) 12.5 (17.0)
BOD:N (BOD Loading g m-2 day-1)
Nitr
ifica
tion
Rate
(gN
m-2
day
-1)
Vary Influent BOD Concentration
Downing and Nerenberg (in press) Water Research
Nitrification rates are is insensitive to influent BOD concentrations
Nitr
ifica
tion
rate
(gN
/m2 -
d)
4 6 12 17 17BOD Loading (g/m2-d)
25
Biofilm Activity: Microsensors
200μm microsensor
HFMbiofilm Measure gradients
through the biofilmDO, NH4
+, NO3-,
NO2-,
Determine fluxes into or out of the biofilm
26
0
2
4
6
8
10
12
14
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Relative Thickness of Biofilm [-]
Con
cent
ratio
n (m
g/L)
Biofilm Gradients
NH4+-N
NO3--N
NO2--N
O2
Biofilm Bulk
Nitr
ifica
tion
flux
(gN
/m2 -
d)
27
Nitrite and Nitrate Production in Biofilm
Downing and Nerenberg (in press) Water ResearchMainly nitrite production (shortcut)
0
0.5
1
1.5
2
2.5
5 (12) 7.5 (17) 12.5 (17)BOD:N (Organic Loading Rate [g m-2 day-1])
Flux
(gN
m-2
day
-1)
Ammonia RemovalNitrite ProductionNitrate Production
29
Biofilm Microbial Structure
Downing and Nerenberg (in press) Water Research
0
2
4
6
8
10
12
14
16
0-30 30-60 60-90 90-120
Distance from Membrane (mm)
Den
sity
(107 c
ells
cm
-3)
AOBNitrobacterNitrospiraOther
Influent BOD:N=7.5
AOB throughout, Nitrobacter near membraneDistance from membrane (µm)
2. Effects of DO and BODHow does the membrane DO affect performance?How much bulk BOD can be tolerated?
31
Experimental System
Recirculation flow
Air into fiber supply
Influent
2 mL/min
Single hollow-fiber membrane
N2 Sparging
Air out of fiber (periodic venting)
Microsensor access ports
Waste
Stir bar
33
Vary membrane pressure (DO)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1 2 3 4
Experiment
Flux
(gN
m-2
day
-1)
Ammonium fluxNitrite fluxNitrate flux
Downing and Nerenberg (in press) Biotechnology and Bioengineering
Tradeoff: high shortcut vs. high nitrification rates
2.2 mg/L 3.5mg/L 5.5 mg/L 5.5 mg/L, aerobic bulk
DO at membrane surface
34
Variable DO - modeling
Downing and Nerenberg (in press) Biotechnology and Bioengineering
Tradeoff exists, but still some shortcut at high DO
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 1 2 3 4 5 6 7 8 9
Oxygen Concentration (mg/L)
Nitr
ogen
Flu
x (g
N m
-2 d
ay-1
)
NitriteNitrateAmmonia
35
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1 3 10
Bulk Liquid BOD Concentrations (g m-3)
Rat
e (g
N m
-2 d
ay-1
)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% D
enitr
ifica
tion
NitrificationN0x ProductionBiofilm Denitrification% denit
Impact of BOD
Downing and Nerenberg (accepted) Applied Microbiology and Biotechnology
BOD slows nitrification, but increases denitrification
1 mg/L 3 mg/L 10 mg/L
36
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 2 4 6 8 10 12
BOD Concentration (g m-3)
Rat
e (g
N m
-2 d
ay-1
)CB NitrificationCB DenitrificationMAB NitrificationMAB Denitrification
Conventional vs membrane biofilm (Model)
CB-Conventional BiofilmMAB-Membrane Aerated Biofilm
Downing and Nerenberg (in press) Biotechnology and Bioengineering
Membrane-aerated biofilm much less sensitive to BOD
38
Pilot scale testing in NYC with Metcalf & Eddy (26th Ward Treatment Plant, PO-55a)Determine the HMBP performance with real wastewater
Pilot Scale Testing
40
Reactor System10 hour HRT120 L active volume2.5 day bulk SRT0.2 m2 membrane surface area
Return Activated Sludge
Settler Influent (BOD, NH4 +)
Hollow Fiber Membranes
Compressed air to membranes
Infl. ammonia: 15-20 mgN/LInfl. BOD: 40-150 mg/L
41
Pilot Scale Testing
0
5
10
15
20
25
30
35
1 28 56 82 100 114 126 139 152 167 181 201 215 232
Day
Con
cent
ratio
n (m
gN/L
)NOx Effluent Ammonia Nitrogen Removed
A DCB
42
0
2
4
6
8
10
12
14
16
18
20
6 12 17 21
Con
cent
ratio
n (m
gN/L
)
HRT
Influent TNEffluent NH3Effluent NOx
Pilot Scale Testing
(hours)
Significant levels of TN removal at higher HRTs
Avg. nitrification rate: 0.35 gN/m2-d
43
Issues for scaleup
Membrane materialsMembrane packing densityMixingBiofilm managementCost analysis
44
CONCLUSIONS• The HMBP is effective for TN removal
• Retrofit
• Short bulk SRTs
• Minimal Donor
• Save energy
• Nitrification insensitive to influent BOD, but sensitive to bulk BOD
• Tradeoff exists between nitrification rates and extent of shortcut
• Promising results, further research needed for scaleup
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