Lessons from Austin’s Full-Scale
Step-Feed BNR Demonstration
Rajendra P. Bhattarai, P.E., DEE
Austin Water Utility, City of Austin
625 East 10th Street, Suite 615
Austin, Texas 78701
Phone: 512-972-0075, Fax: 512-974-3504
The Fifth Annual W. Wesley Eckenfelder Lecture
Design into Practice: Leveraging Best Design Applications
The University of Texas at Arlington
June 23, 2015
W. Wesley Eckenfelder (1926-2010)
• Friend and colleague
• Teacher
• Author
• Mentor
• Innovator and entrepreneur
• Pioneer in industrial water
quality management and
wastewater treatment
• And a great human being
Presentation Outline
• Background
• Step-Feed
• BNR System Used
• Operating Characteristics
• Results
• Lessons Learned
Background
• Austin’s wastewater treatment plants discharge to the Colorado River
• Waterbody of exceptional quality
• Nutrient removal required in future
• Need for demonstration of N & P removal
• Goal: TP < 1mg/L; TN < 10 mg/L
• Full-Scale Step-Feed BNR operated at South Austin Regional (SAR) WWTP for two years: January 1996 - December 1997
Activated Sludge
Influent
RAS
WAS
Aerobic Effluent
Influent
RAS
WAS
Aerobic Effluent
10 MGD MLSS = 3,000 mg/l
For 25% increase in treatment capacity
12.5 MGD MLSS = 3,750 mg/l High MLSS can overload
secondary clarifier
Activated Sludge
Step-Feed Primary Effluent
4,900
MLSS
3,800
MLSS
3,300
MLSS
3,000
MLSS
Aerobic
Average MLSS = 3,750 mg/l
RAS WAS
Final
Clarifier
40% 30% 20% 10%
Advantages of Step-Feed
• Operational Flexibility
• Higher MLSS results in higher capacity
without increasing solids loading to
secondary clarifiers
• Maximize use of existing facilities
• Better handling of peak flows
• Robust and stable operation
Q
Anaerobic Aerobic
Q
WAS RAS
Anoxic
Nitrate Recycle, 1-2Q
Anoxic Recycle, 1-2Q
A staged reactor configuration is provided by using at least two complete-mix
cells in series for each zone of the biological reactor.
Virginia Initiative Plant (VIP) Process
(NRCY)
(ARCY)
Step-Feed Primary Effluent
4,900
MLSS
3,800
MLSS
3,300
MLSS
3,000
MLSS
Aerobic
RAS WAS
Final
Clarifier
40% 30% 20% 10%
BNR demonstration system at SAR
used the “Step-Feed BNR Process” --
combination of VIP and Step-Feed
PE ARCY PE ARCY
ANR ANX AER ANR ANX AER AER
RAS NRCY
SOUTH AUSTIN REGIONAL WASTEWATER TREATMENT PLANT
LIFT
STATIONS GRIT
BASINS
INF
LU
EN
T
BA
R
SC
RE
EN
S
PRIMARY
CLARIFIERS
FLOW
EQUALIZATION
DIVERSION
BOX
ACTIVATED
SLUDGE
AERATION
BASINS
SECONDARY
CLARIFIERS CHLORINATION
SCREENINGS
AND GRIT TO
LANDFILL
EFFLUENT
FILTERS
DECHLORINATION
DISCHARGE TO
THE COLORADO RIVER
EF
FLU
EN
T
RETURN ACTIVATED SLUDGE
WASTE ACTIVATED SLUDGE SLUDGE
BLENDING GRAVITY
THICKENER
SLUDGE
PUMPS
TO HORNSBY BEND BIOSOLIDS MANAGEMENT PLANT
FILTER BACKWASH
SUPERNATANT REUSE
PUMPS
TO GOLF
COURSE
IRRIGATION
PR
IMA
RY
SL
UD
GE
South Austin Regional Wastewater Treatment Plant
Train A Train B
BNR
Control
Activated Primary for VFA Generation
Raw
Primary Effluent Wastewater
containing VFAs
Return Primary Sludge
(Elutriates Sludge)
Waste Primary Sludge
(To Thickening)
Original Aeration Basin Flow Path
Effluent Channel
Influent Channel
RA
S C
han
nel
(RAS and PE mix)
Primary Effluent
Flow Diversion Box
Aeration Basin Step-BNR
Modified Flow Path
Effluent Channel
Influent Channel R
AS
Channel
Primary Effluent
Normal Input of
Secondary Influent
Flow Diversion Box
AER
AER
Pass 4
AER
Pass 3
AER
Pass 2
AER
Pass 1
AER ANR
ANX
ANR
ANX
ANR
ANX
ANR
ANX
ANR ANR
ANX ANX
ANR ANR
ANX ANX AER AER
48” Bypass
Indicates
Internal
Recycle
RAS (Alt)
Baffles added to
Existing Aeration Basins
to form Anaerobic,
Anoxic and Aerobic
Zones
Volume, million gallons
Step- BNR Control
Total 2.6 2.6
Anaerobic 0.4 0
Anoxic 0.4 0
Aerobic 1.8 2.6
Baffles for Anaerobic, Anoxic and Aerobic Zones
Aeration Basin on
the “Control” side
Activated Sludge
No persistent foam
Only air bubbles
BNR Basins: Aerobic Zone in the
foreground; Anoxic
and Anaerobic Zones
in the background.
Comparatively more
foam and scum than
“control”
BNR Basins:
Anaerobic Zone
in the foreground;
Anoxic and
Aerobic
Zones in the
background
Close-up view of the Anaerobic Zone
Wastewater Temperature: 19o- 30
o C
16
18
20
22
24
26
28
30
32
Infl
ue
nt
Te
mp
era
ture
,
o C
1 7 6 5 4 3 2
Operating Periods:
1-M
ar
12
-Ap
r
24
-Ma
y
5-J
ul
16
-Au
g
27
-Se
p
8-N
ov
20
-De
c
31
-Ja
n
14
-Ma
r
25
-Ap
r
6-J
un
18
-Ju
l
29
-Au
g
10
-Oc
t
21
-No
v
2-J
an
Test flows were 6 to 20 MGD
0
2
4
6
8
10
12
14
16
18
20
Pri
ma
ry E
fflu
en
t F
low
, M
GD
BNR
CONTROL
Operating Periods:
1 7 6 5 4 3 2
1-M
ar
12
-Ap
r
24
-Ma
y
5-J
ul
16
-Au
g
27
-Se
p
8-N
ov
20
-De
c
31
-Ja
n
14
-Ma
r
25
-Ap
r
6-J
un
18
-Ju
l
29
-Au
g
10
-Oc
t
21
-No
v
2-J
an
Jan
-96
Mar-
96
Ju
n-9
6
Sep
-96
Dec-9
6
Mar-
97
Ju
n-9
7
Sep
-97
Dec-9
7
Period 7
Period 6
Period 5
Period 4
Period 3
Period 2
Period 1
Startup
Flow and Temperature Defined Operating Periods
Steady 8 MGD; ~22o C
Steady 8 MGD; ~27o C
(Construction Outage)
9-20 MGD; ~22o C
12 MGD; ~28o C
10-13 MGD; ~27o C
Improved APC, Steady 6 MGD; ~22o C
0
10
20
30
40
50
60
70
80
Net
TS
CO
D P
rod
uced
, m
g/L
1 7 6 5 4 3 2
Activated Primary Clarifier
worked well at times 1
-Ma
r
12
-Ap
r
24
-Ma
y
5-J
ul
16
-Au
g
27
-Se
p
8-N
ov
20
-De
c
31
-Ja
n
14
-Ma
r
25
-Ap
r
6-J
un
18
-Ju
l
29
-Au
g
10
-Oc
t
21
-No
v
2-J
an
BOD loads similar to Control
0
5,000
10,000
15,000
20,000
25,000
30,000
PE
BO
D5,
lb/d
CONTROL
BNR
1 7 6 5 4 3 2
1-M
ar
12
-Ap
r
24
-Ma
y
5-J
ul
16
-Au
g
27
-Se
p
8-N
ov
20
-De
c
31
-Ja
n
14
-Ma
r
25
-Ap
r
6-J
un
18
-Ju
l
29
-Au
g
10
-Oc
t
21
-No
v
2-J
an
MCRT lower than in Control
0
5
10
15
20
25 A
ero
bic
MC
RT,
days
CONTROL
BNR
1 2 3 4 5 6 7
1-M
ar
12
-Ap
r
24
-Ma
y
5-J
ul
16
-Au
g
27
-Se
p
8-N
ov
20
-De
c
31
-Ja
n
14
-Ma
r
25
-Ap
r
6-J
un
18
-Ju
l
29
-Au
g
10
-Oc
t
21
-No
v
2-J
an
SVI for BNR was higher
0
20
40
60
80
100
120
140
160
180 1
-Ma
r
12
-Ap
r
24
-Ma
y
5-J
ul
16
-Au
g
27
-Se
p
8-N
ov
20
-De
c
31-J
an
14
-Ma
r
25
-Ap
r
6-J
un
18
-Ju
l
29
-Au
g
10
-Oc
t
21
-No
v
2-J
an
Slu
dg
e V
olu
me
In
de
x (
SV
I),
mL
/g
BNR
Control
Excessive
Foaming
1 2 3 4 5 6 7
Excessive Foaming
in BNR Basins due
to Nocardia Growth
and poor hydraulics
Both systems nitrified well E
fflu
en
t N
H3 -
N,
mg
/L
BNR
CONTROL
Trend lines are seven day moving averages
1 7 6 5 4 3 2
10.00
1.00
0.10
0.01
1-M
ar
12
-Ap
r
24
-Ma
y
5-J
ul
16
-Au
g
27
-Se
p
8-N
ov
20
-De
c
31
-Ja
n
14
-Ma
r
25
-Ap
r
6-J
un
18
-Ju
l
29
-Au
g
10
-Oc
t
21
-No
v
2-J
an
0
5
10
15
20
25
30
35
Eff
luen
t N
O 3 -N
, m
g/L
BNR
CONTROL
1 7 6 5 4 3 2
Nitrogen removal was good 1
-Ma
r
12
-Ap
r
24
-Ma
y
5-J
ul
16
-Au
g
27
-Se
p
8-N
ov
20
-De
c
31
-Ja
n
14
-Ma
r
25
-Ap
r
6-J
un
18
-Ju
l
29
-Au
g
10
-Oc
t
21
-No
v
2-J
an
BNR Ortho-P Profile
3/13/96 to 4/8/96 PASS-1 PASS-2 PASS-3 PASS-4
2
4
6
8
10
12
PR
I1B
AN
R1W
AN
R1E
AN
X1E
AN
X1W
AE
R1S
AN
R2W
AN
R2E
AN
X2E
AN
X2W
AE
R2
N
AN
R3W
AN
R3E
AN
X3E
AN
X3W
AE
R3S
AE
R4S
ZONES
Ort
ho
-P,
mg
/ L
P removal was variable
0
1
2
3
4
5
6
7
Eff
luen
t O
rth
o-
P,
mg
/L BNR CONTROL
1 7 6 5 4 3 2
1-M
ar
12
-Ap
r
24
-Ma
y
5-J
ul
16
-Au
g
27
-Se
p
8-N
ov
20
-De
c
31
-Ja
n
14
-Ma
r
25
-Ap
r
6-J
un
18
-Ju
l
29
-Au
g
10
-Oc
t
21
-No
v
2-J
an
Lessons Learned
• BNR systems not that different from
other treatment systems
• But they do require some understanding
and familiarity
• BNR systems need more operational
attention than conventional activated
sludge
Lessons Learned (continued)
• Volatile Fatty Acids crucial for BNR -
especially for phosphorus removal
• VFA production depends on Activated
Primary Clarifier operation
• BNR systems more prone to foaming
than conventional activated sludge
• Foaming can be controlled using
polymers, water sprays and chlorine
Lessons Learned (continued)
• Allow sufficient hydraulic head between
different zones for easy removal of
scum and foam
• Provide free-flow path at water surface
through all zones to secondary clarifiers
for scum removal
• Good hydraulics for flow split critical for
Step-feed
Lessons Learned (continued)
• Nitrogen removal depends on F/M in
anoxic zones
• Phosphorus removal depends on F/M in
anaerobic zones (especially VFAs)
• Phosphorus removal is directly
proportional to the amount of
phosphorus released in the anaerobic
zones
Questions,
Comments?
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