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

Raj.Bhattarai@austintexas.gov

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?