14/05/2015

1

1

Hybrid activated sludge/biofilm processes

(IFAS)

SET AS

Hallvard Ødegaard

1Prof. em. Norwegian University of Science and Technology (NTNU)

CEO Scandinavian Environmental Technology (SET) AS hallvard.odegaard@ntnu.no

Activated sludge: 100 plus 1 years

New trends and perspectives

University of Palermo, 11.05.2015

2

What is an Integrated Fixed-film Activated Sludge (IFAS) system ?

An IFAS system involves the combination of a suspended biomass (activated sludge) and an attached biomass (biofilm) in the same reactor

SET AS

Ringlace IFAS system Fixed media IFAS system

Examples of systems that are less used today

MBBR IFAS system

The system that are most commonly used today

14/05/2015

2

3

SET AS

a. AccuFAS

Courtesy Brentwood Ind.

b. Bio-Blok

Courtesy Expo-Net

d. Ringlace

Courtesy Kajima

Aquatech

c. PU foam cubes

Courtesy Exile Machine

e. Biotextil Cleartec

Courtesy HYDROK

Various fixed and moving carriers

Courtesy Biowater

Technology

f. K1 g. K3 h. K5 i. BiofilmChip M j. ABC k. BWT S

• 500 m2/m3 bulk

• 25 x 10 mm

diameter/depth

• 500 m2/m3 bulk

• 9.1 x 7.2 mm

diameter/depth

• 800 m2/m3 bulk

• 25 x 3.5 mm

diameter/depth

• 1200 m2/m3 bulk

• 48 x 2.2 mm

diameter/depth

Courtesy AnoxKaldnes Courtesy Aqwise

Various suspended (MBBR) carriers

• 650 m2/m3 bulk

• 13 x 13 mm

diameter/depth

• 650 m2/m3 bulk

• 18.5 x 14.5 x 7.3 mm

length/width/depth

4

The Moving Bed Biofilm Reactor (MBBR)

SET AS

14/05/2015

3

5

The MBBR-based IFAS - system

SET AS

a. MBBR in whole reactor b. MBBR in last part of reactor c. MBBR in middle part of reactor

e. MBBR IFAS for N-removal d. MBBR IFAS for N- and P-removal d. BAS + IFAS MBBR

• Carrier filling fraction: anything from 0% to 65 % • Commonly 50-55 % in anoxic and 55-60 % in aerobic reactors

6

Some early Norwegian IFAS experiments (Rusten et al, 2003)

SET AS

0

2

4

6

8

10

12

1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0

Eff

lue

nt

NH

4-N

, m

g/L

Aerobic SRT, days

Hybrid (MLSS only)

Hybrid (MLSS +biofilm)

AS control (MLSS)

Temp. comp. to 15 oC.

Effluent NH4-N concentrations versus aerobic SRT's for IFAS and AS pilot-plant control trains – filling fraction: 18 %

14/05/2015

4

7

Influence of reactor DO on effluent NH4-conc. and

biofilm carrier nitrification rate (Broomfield pilot plant)

SET AS

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1 2 3 4 5 6B

iofi

lm c

arr

ier

nit

rif.

rate

, g

NH

4-N

/m2/d

Reactor DO, mg/L

Measured

Model

Batch test of carriersfrom last reactor.Temp. comp. to 15 deg. CModel: rN = k*(SN)0.7

b0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

2 3 4 5 6 7

Eff

luen

t N

H4-N

, m

g/L

Reactor DO, mg/L

R3 daily avg. DO

Power (R3 dailyavg. DO)

a

rN = nitrification rate (g NH4-N/m2. d) k = reaction rate coefficient n = reaction order constant, can be estimated at n = 0.7 Sn = rate-determining ammonium concentration, mg NH4-N/L (can be estimated at Sn = (DObulk – 0.5)/3.2

rN = k . (Sn)n

8

SRT Vs Temperature

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Temperature, C

SR

T, d

ATV Design Curve

Nitrifier Growth Rate

Broomfield (4.7 days at 13 C)

Cheyenne (4.5 days at 9 C)

Yucaipa (2.3 days at 18 C)

Taos (5.2 days at 8 C)

Oxford

(3.9 days at 11C) Fields Point & Flagstaff (3.3 days at 14 C)

James River (2.7

days at 14 C)

Greensboro (5.25 days at 14 C)

Springettsbury

(2.4 days at 10 C)

Lubbock (3.8 days at 15 C)

Fairplay (2.5 days at 5 C)

New Castle (4.1 days at 10C)

Crestted Butte (3.2 days at 7.5 C)

Georgetown (5.0 days at 9 C)

Design SRT vs temp for full scale IFAS

systems (installed by ANOXKALDNES)

C. Johnson, 2009 Mamaroneck (1.8 days at 13 C)

14/05/2015

5

9

Distribution of nitrification activity between attached and suspended biomass

SET AS

0

1

2

3

4

5

6

7

8

9

12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0

Spec

ific

Am

mo

nia

Oxi

dat

ion

Rat

e,

mg-

NH

3-N

/g-T

SS/h

r

Temperature, C

Carriers

Suspended Phase

Specific nitrification activity in attached and suspended biomass versus temperature

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

12 14 16 18 20 22 24 26 28 Fr

acti

on

of

Tota

l NH

3-N

Oxi

dat

ion

A

ctiv

ity

Temperature, C

Carriers

Suspended Phase

Fraction of NH3-N oxidation activity in attached and suspended biomass versus temperature

McQuarrie and Thomas (2009)

10

Denitrification in MBBR-based IFAS plants

SET AS

• IFAS in Pre-DN - Not very common

• IFAS in post-DN – Quite possible

• Higher DN-rate in pre-anoxic reactor because more carbon seems to be left after short SRTsusp nitrification

• Post-anoxic IFAS reactor efficient

• IFAS may, in principle, be used in all reactors

14/05/2015

6

11

Biological P-removal in MBBR-based IFAS plants

Onnis-Hayden et al (2011) – Broomfield WWTP study:

• More EBPR activity in suspended biomass

– 20-30 % in mixed liquor biomass – 3-8 % in biofilm media biomass

• N-removing and P-removing populations prefer conflicting SRT's,

– hence they should be decoupled – allowing for separate SRT control

SET AS

Bio-P may profit by using IFAS with UCT design because:

• The EBPR biomass is mixed with little nitrification biomass

• Nitrification is better promoted since most of the nitrification biomass will not pass the anaerobic stage

12

Biomass separation in IFAS

0

50

100

150

200

250

300

350

Dec-03 Jan-04 Feb-04 Mar-04

SV

I (m

L/g

)

Control IFAS

Comparison on SVI in two parallel lines at Lakeview WWTP, Ontario, Canada , (Briggs, 2009)

IFAS generally seems to improve settleability

SET AS

Pre- and post IFAS SVI at Field's Point WWTP, Providence, RI, USA (Wilson et al., 2012)

14/05/2015

7

13

Anammox in IFAS (Christensson et al, 2013)

BiofilmMedia

Liquid

Nitritation

NH4+

NO2-AOB

Anammox

N2O2

Aerobic

AnoxicBiofilm

Media

Liquid

Nitritation

NH4+

NO2-AOB

Nitritation

NH4+

NO2-AOB

Anammox

N2

Anammox

N2O2O2

Aerobic

Anoxic

MBBR

= 0.5-1.5

mg/L

AOB in biofilm = NO2- limitation

IFAS

SET AS

Biofilm Media

Liquid

Nitritation

NH4+

NO2-

AOB

Anammox

N2O2

AnoxicMedia

Liquid

Nitritation

NH4+

NO2-

AOB

Anammox

N2O2

Anoxic

< 0.5

mg/L

Flocs (1-3 g/L)

AOB in flocs = less NO2- limitation

14

BioFarm concept = Providing seeded carriers for rapid start-up of future full-scale ANITATM Mox units Seeded carriers

ANITA™ Mox – Sjölunda WWTP, Malmö (Sweden)

• 4 x 50m3 MBBR • Capacity = 200 kgN/d • 800-1200 mgN-NH4/L • 1st ANITA™ Mox reference • Flexibility for fullscale testing

SET AS

14/05/2015

8

15 Full-scale test results ANITA™Mox , Sjölunda WWTP (Christensson et al, 2013)

SET AS

• Very high N-removal rate up to 3 kg NH4-N/m3.d (7.5 g NH4-N/m2.d) • 2.5-3 times higher than in pure MBBR design • Energy consumption : 1.2 kWh/kg NH4-N removed

0

0,5

1

1,5

2

2,5

3

3,5

NH

4 l

oa

d &

re

mo

va

l (k

gN

/m

3.d

)

NH4-load

NH4-removal

0

10

20

30

40

50

60

70

80

90

930 950 970 990 1010 1030 1050 1070 1090 1110 1130 1150

%N

H4

an

d %

TN

re

mo

va

l

Days

%TN-removal

%NH4-removal

%NO3-prod : NH4-rem

MBBR Tran-

sition

IFAS

• K5 – filling fraction 50 % • DOMBBR = 1.0 - 1.3 mg/l • DOIFAS = 0.2 - 1.0 mg/l • MLSSMBBR = 20–400 mg/l • MLSSIFAS = 1800 – 4600 mg/l

16

Design of IFAS systems Four design criteria are recognized to be important to IFAS system design:

1. The ammonia flux (JF,NH3-N), 2. The biofilm area 3. The bulk liquid DO concentration (SO2), 4. The bulk liquid ammonia concentration (SN)

McQuarrie et al (2010) introduced a fifth design parameter :

5. The Nitrification Safety Factor (SFNit.),

This fifth design parameter characterizes the capability of nitrifiers to grow and reproduce in the suspended biomass independently of the biofilm.

SFNit = aerobic suspended solids retention time

calculated nitrifier minimum SRT

Four approaches for IFAS system design as proposed by McQuarrie et al. (2010)

Design approach

SFNitrification Effluent ammonia target, mg NH3-N/L

Install media in reactor?

Parameter for determining (JF, NH3-N).

R-2 R-3 R-2 R-3

A

B

C

D

0.5 to 1.0

0.5 to 1.0

1.0 to 1.5

1.5 to 2.0

< 2.0

< 1.0

< 1.0

< 1.0

Yes

Yes

Yes

Option1

No

Yes

Option1

No

SO22

SO2

SO2

SO2

-

SN

SN

-

1 Plastic carriers added to reactor to increase reliability against system perturbations

2 Contribution of nitrification achieved by suspended growth component of the IFAS system is ignored

14/05/2015

9

17

SET AS

Design of IFAS systems

0

1

2

3

4

5

6

0 1 2 3 4 5 6 7 8

g N

H4-N

/kg M

LS

S .

h

C/N-ratio in bioreactor (BOD5/tot N)

Empirical design methods – example Ødegaard (2008)

0

0.5

1

1.5

2

2.5

3

3.5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

DN

-rate

, g

NO

x-N

/kg M

LS

S. h

C/N-ratio, g BOD5,in/g NOx-N removed

0,4

0,45

0,5

0,55

0,6

0,65

0,7

0,75

0 1 2 3 4 5 6 7 8Nitrification

rate

co

eff

icie

nt,

k

C/N ratio in aerobic ractor (BOD5/NH4-N)

rN = k . (Sn)n

Mathematical modelling design methods Mathematical models are available, that combine AS- and BF-models. They require, however, special modelling skills to be used correctly.

0

0,2

0,4

0,6

0,8

1

1,2

0 2 4 6 8 10

Cor

rect

ion

fact

or, K

MLSS SRT (d)

K – fraction of nitrification

taking place on carrier

18 Compartment partition

SET AS

Placing the media in an early stage may have several advantages: • CNH4 is highest in early stages favoring the

nitrification capacity of the attached biomass • DO may be reduced in the last compartment

(less DO return) since CNH4 here is low • Low intensity of mixing in last compartment

improves flocculation • "Seeding" of nitrifiers from attached to

suspended biomass is favored

DO/Temp. mg O2 L-1 / aver. oC 5.00 /13.8

SRT d 3.4

Biofilm nitrification rate (10oC) g NH4-N.m-2d-1 (g NOx-N.m-2d-1) 0.92 (1.02)

Biofilm biomass nitrification rate (10oC) mg NH4-N.g VSS-1 h-1 2.37

Typical susp. biomass nitrific. rate (10oC) mg NH4-N.g VSS-1 h-1 1-2

Suspended biomass nitrification rate (10oC) mg NH4-N.g VSS-1 h-1 2.80

Trapani et al, 2012

14/05/2015

10

19

SET AS

Oxygen transfer

• Oxygen transfer is enhanced by the presence of carriers

• The higher the filling fraction, the better SOTR

• Influence dependent on carrier design. Suppliers should provide SOTR data

• Mamaroneck wastewater treatment plant, Westchester County, New York Full scale clean water oxygen transfer test when using a medium bubble aeration system (with 55 % K3 carriers) :

SOTR : 13 g O2/Nm3 . m

0,00

2,00

4,00

6,00

8,00

10,00

12,00

14,00

16,00

Renvatten, grov K3, 30% grov K3, 50% grov

gO2/

Nm

3 m

Clean

water

K3

30 %

K3

50 %

K3

30 %

g O

2/N

m3 . m

16

14

12

10

8

6

4

2

0

Christensson, 2013

20

Approach velocity and sieve design

Recommended sieve velocities:

• Aerated sieve: 50-60 m/h

• Approach velocity: < 30 m/h at peak flow at a length/width-ratio of 1.0 decreasing linearly to 15 m/h at a length/width-ratio of 3.0.

SET AS

Upgrading of long narrow AS –tanks:

3

2 1

From primary setting

1. Bioselector 2. Anoxic zone 3. Oxic zone To biomass clarifier

Influent channel

Efffluent channel

Proposed (AECOM) solution for Sha Tin WWTP, Hong Kong

Oxford WWTP, UK

14/05/2015

11

21

Example Marquette-Lez-Lille, France (Veolia, 2013)

SET AS

Pre-DN Anaerob. DN IFAS-N De-

ox

Post-

DN Post-

aerob.

De-

gas.

Clarifier Filter

Mixed liqour recirculation

Sludge recirculation

Backwash water

CH3OH FeCl3

Before Today

22

Example: Sharjah WWTP, UAE Combining high-rate MBBR and IFAS for upgrading

Task: Convert a secondary treatment AS plant into a fully nitrifying plant at a double load - without bioreactor volume expansion

20 % of V50 % K3 fill

50 % of VNo media

30 % of V50 % K3 fill

ExtremeNH4-N peakscoming inbecause oftrucked ww

Total reactorvolume:

V=13000 m3

20 % of V50 % K3 fill

50 % of VNo media

30 % of V50 % K3 fill

ExtremeNH4-N peakscoming inbecause oftrucked ww

Total reactorvolume:

V=13000 m3

20 % of V50 % K3 fill

50 % of VNo media

30 % of V50 % K3 fill

ExtremeNH4-N peakscoming inbecause oftrucked ww

Total reactorvolume:

V=13000 m3

SET AS

Parameter

Results performance tests

Nov 2008- Jan 2009 April 2010-May 2010

mg/l % rem mg/l % rem

BOD5 7,5 97,3 6,4 97,6

NH4 – N (TKN) 4,7 92,9 0,92 97,0 (98,3)

14/05/2015

12

23

Conclusions

SET AS

1. IFAS is very compact compared to AS and is especially suitable when upgrading for nitrification/N-removal

2. Nitrification in IFAS is essentially independent of SRT (SRTae.,susp may be < 2d)

3. Nitrification activity is 3-4 times higher in the attached biomass than in the suspended biomass ( at: T <15 oC, SRT < 3 d, C/Nincoming: 3-4, DO: 3-5 mg/l)

4. The lower the temperature, the higher is the fraction of the total nitrification that is taking place in the biofilm

5. Recommended DOdesign : 4-6 mg/l at peak load

6. High oxygen transfer caused by carrier presence : 12-14 g O2/Nm3 . m (medium bubble at filling fractions > 50 %)

7. IFAS may also be used in anoxic and anaerobic reactors, but benefits are lower than in aerobic reactors

8. Design knowledge is not at the same level as AS design

9. IFAS operation seems to be more robust than that of AS

24

Acknowledgements

I would like to acknowledge:

– Magnus Christensson, AnoxKaldnes, Sweden

– Kim Hellesøj Sørensen, WABAG, Switzerland

for being my co-authors for the Hybrid Systems chapter in the Activated Sludge 100 years book (IWA Publishing) and:

– James P. McQuarrie, Metro Wastewater Reclamation District, Denver, Colorado, USA,

– Joshua P. Boltz, CH2M HILL, Tampa, Florida, USA,

– Chandler Johnson, World Water Works, Oklahoma City, Oklahoma, USA,

– Mark Steichen, Black and Veatch, Kansas City, Missouri, USA,

– Daniele di Trapani, Università degli Studi di Palermo, Italy

– Bjørn Rusten, Aquateam, Norway

for their valuable support and comments during the preparation of that chapter