Two Different Ways to Achieve Low BNR Limits

TWO DIFFERENT WAYS TO
ACHIEVE LOW BNR LIMITS
1. AERATED ANOXIC
2. IFAS/MBBR
Presented by Tom Larsen
Thursday January 23, 2014
Aerated Anoxic and IFAS
January 23, 2014
©2014 Evoqua Water Technologies LLC
PAGE 1
Current Aerated Anoxic Design Practices
Variations on oxidation ditch with aerated tanks
in series to achieve BNR
Biological Nutrient Removal (BNR)
• Nitrification
• Denitrification
• Phosphorus removal
• Reduce alkalinity requirements
• Reduce process oxygen requirements
• Control sludge settleability
Aerated Anoxic Tank (Channel)
A biological reactor in which the oxygen delivery is less
than the oxygen demand, thereby, creating a zone of
continuous oxygen deficiency (avg. DO levels between
0 and 0.5 mg/L)
Aerobic tank (channel)
A biological reactor in which the oxygen delivery is
equal to or greater than the oxygen demand, thereby,
creating a zone of continuous oxygen residual (avg. DO
levels between 1.5 and 2.5 mg/L
DO Profile in Orbal
0
0.5
2
Aerated Anoxic – Oxygen Deficit
Aerobic – Oxygen Residual
• First tank is high substrate operated at an oxygen deficit – low DO
• Last tank is low substrate operated with an oxygen residual – high DO
Oxygen Demand and Supply
% Oxygen Demand
100
80
60
demand
40
supply
20
0
1
2
Channel
3
Nitrogen Removal Methodologies
Pre-anoxic
N2(g)
Q
QINT
anoxic
Aerobic
Q
O2
QRAS
Sim-pre N
2(g)
QINT
Q
Aerated
Anoxic
QW<<Q
Aerobic
Q
O2
QRAS
QW<<Q
Sim-Pre MLSS Recycle
Combines the process kinetics of methodologies for improved total
nitrogen removal:
Simultaneous nitrification-denitrification
Pre-denitrification
Denitrification Efficiency (assuming 100% RAS)
100
% Denitrification
90
80
Sim-Pre
70
Pre
60
50
0
0.5
1
1.5
2
2.5
MLSS Recycle:Influent
3
3.5
4
Lexington-Rockbridge, VA - Orbal
Design
3.0 MGD
6 mg/l TN
Aerated anoxic
MLE
Actual
2.5 - 6 mg/l TN (no supp. C)
Nitrogen Removal Performance
St. Charles, MO
•
•
7.5 MGD ADF with 24.4 MGD peak
30’ Wide channels with bridge mounted aerators
•
Torque tube disc aerator also available
Vertical Loop Reactor
Swatara, PA – VertiCel
• Design
• 6.3 MGD
• 6 mg/l TN
• 0.8 mg/l TP
• Aerated anoxic
• 5-stage Bardenpho
• Actual
• 3 - 6 mg/l TN (no supp. C)
• 0.2 - 0.8 mg/l TP(less chemical)
Sample problem – VertiCel
Existing primaries converted to RAS
tank with mixers and aerated anoxic
channel with disc aerators
Middle aeration basin converted to a
VLR
Outside aeration basins stay as fine
bubble
Internal mixed liquor recycle pumps
from aeration back to VLR
Sample problem – key parameters
VertiCel
MLSS 4,100 mg/l
SRT 11 days
RAS = 100% of ADF
IR = 300% of ADF
Operating power = 150 hp
Secondary Clarifiers
SOR average = 433 gpd/ft2
SOR peak = 996 gpd/ft2
SLR average = 29.5 lbs/day/ft2
SLR peak = 42 lbs/day/ft2 (step feed)
Configurations
IFAS Process
Sludge
Treatment
MBBR Process
Sludge
Treatment
Biomass Carrier - Core of the Process
• Evoqua biomass carriers
• Patented carrier design
• Biological tested for surface
validation
• Tested under nitrification, BOD
oxidation, and denitrfication
CM-10D Ammonia performance
140
20
18
120
• Test surface area results ~800
m2/m3
BOD load to
reactors
60
12
12 g/m2/d
80
5.5 g/m2/d
14
3.9 g/m2/d
Effluent NH3N, competition
10
8
6
40
4
20
2
CM10D
effluent
NH3
0
0
10
20
30
40
50
60
70
80
90
100
110
Day
120
130
140
150
160
170
180
190
200
0
210
BOD loading (g/day)
100
NH3 (mg/l)
• Trade name: BioSphere
16
Major components – Retention Screens
•
All retention screen are stainless steel
•
Wedge wire or perforated plate
construction
•
Minimum screen opening 7mm
•
All supports supplied
•
Purging supplied as necessary
Major Components of Biosphere - Aeration
Aeration
Biosphere process uses aeration
for oxygen transfer and mixing.
• Self sealing diffuser option
available
• Stainless steel or PVC
construction
• Low to no maintenance
required.
• Actual clean water OTE testing
data available.
Design of a nitrification MBBR considers multiple
variables
 Influent sBOD should
be less than 5 mg/L
 To achieve this,
multiple stages are use,
i.e. BOD stage then
nitrification stage
 Competition for DO
exists in biofilm
 To keep all layers
aerobic, high DOs are
required
To illustrate why the DO is elevated in a MBBR we must
look within the biofilm
Biofilm layers
SDNR occurs deep in
aerobic biofilm
Bulk liquid
MTBL
Media surface
Although DO is high
for MBBR, this
results in nitrification
rates 2 to 3 times
higher than activated
sludge at the same
DO and temperature
JNH3, g/m2/d,
DO, mg/l
6 mg/l DO
4.5 mg/l DO
Neptune Beach, FL required to decrease nitrogen by
converting from contact stabilization to IFAS
Effluent nitrogen before and after implementation of the
IFAS process
After installation of the IFAS system, the plant was able
to meet the new TMDL standards
Sample problem – IFAS
Existing primaries converted to
anaerobic tanks with mixers
Aeration basins segmented into 6 zones
Pre-Anoxic, Aerobic zone 1,
Aerobic zone 2, MLSS IR zone,
post anoxic, re-aeration zone
Sample problem – key parameters
IFAS
MLSS 3,500 mg/l
SRT 7.5 days
RAS = 100% of ADF
IR = 175% of ADF
Operating power = 325 hp
Supplemental carbon = 500 – 1000 lbs/day
Secondary Clarifiers
SOR average = 433 gpd/ft2
SOR peak = 996 gpd/ft2
SLR average = 23 lbs/day/ft2
SLR peak = 38 lbs/day/ft2
Aerated Anoxic and IFAS
January 23, 2014
©2014 Evoqua Water Technologies LLC
PAGE 26
Thank you for your
attention
Contact info:
Tom Larsen
[email protected]
phone: 262-521-8482
Aerated Anoxic and IFAS
January 23, 2014
©2014 Evoqua Water Technologies LLC
PAGE 27

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