Electronic Nose for Reactor Stability Monitoring of an Agricultural Co-

digestion Biogas Plant

Environmental Sciences and Management Department

University of Liège

Gilles.Adam@ulg.ac.be

G. Adam S. Lemaigre P. Delfosse A-C. Romain

1 Progress in biogas III, 10-11 September, 2014, Stuttgart

2 Pearce et al., 2003

What is an electronic nose (e-nose) ?

It’s an array of complementary low-specificity gas sensors increased specificity using sensor array pattern (like a signature)

Introduction

Why e-nose technology?

Introduction

3

• Anaerobic digestion process monitoring:

• Online monitoring: [CH4], [CO2], biogas production, pH

• Offline analysis: alkalinity, Volatile Fatty Acids (individuals/total), etc.

• No online tool for early warning of anaerobic digestion process disorders

• E-nose advantages:

• Online monitoring

• Gas phase sampling (easier than liquid-phase sampling in anaerobic reactors)

• Rapid turn-over of gas phase of the reactor (hours)

Sample Transport

(days)

Register sample (hours)

Measure (hours-days)

Results transmission

Decision

Sample Measure (minutes)

Decision

Adapted from Holm-Nielsen, 2008

Actual situation

Ideal situation

Phase I: 100 L pilot-scale CSTR monitoring

4

e-nose = array of 6 low-specificity gas sensors and a dilution system (25x)

Liquid phase Total solids [%], volatile solids [%TS] pH Alkalinity [ml CO2] NH4

+ [g L-3]

Gas phase CH4 [%], CO2[%], H2S (ppm), H2 (ppm) E-nose

Material and methods

Phase II: Full-scale reactor monitoring

5

Material and methods

6

Material and methods

E-nose: array of 7 low-specificity commercial gas sensors (Figaro Engineering inc.)

During e-nose monitoring (650 days): weekly: VFA, VS, TS, VFA/TIC (FOS/TAC) Every 2 weeks: total ammonia nitrogen (TAN)

7

Faascht farm (BE)

Co-digestion biogas plant of 750 kW 3 CSTR + two storage tanks + Digestate drying unit Substrates (18 000 T): •Food industry waste (54 %) •Cattle manure/slurry (33 %) •Maize silage (8 %)

Limited process monitoring capabilities: On-line: CH4, CO2, H2S and O2 (prior to CHP) When low gas quality/production: VFA, N-NH4

+ in the sludge

Material and methods

8

Results – Pilot-scale monitoring

0

0.5

1

1.5

2

2.5

3

0

1

2

3

4

5

6

7

8

TIC

(m

l CO

2 g

-1, N

-NH

4 (

g kg

-1)

pH

pH

TIC

N-NH4

0

2

4

6

8

10

OLR

(gV

S L-1

d-1

), g

as

pro

du

ctio

n r

ate

(m³

m-3

d

ay--1

)

OLR

biogas production

0

2

4

6

8

10

12

0 10 20 30 40 50 60 70 80 90 100 110 120

T2/l

im9

9 ,

SPE/

SPEl

im9

9

Time (days)

ratioT2/lim99

ratioQ/lim99

limit

Alkalinity decrease

pH decrease

E-nose indicators

9

0

20

40

60

80

100

CH

4 a

nd

CO

2 c

on

ten

t (%

)

CH4 CO2

0

1

10

100

1000

10000

0

2000

4000

6000

8000

10000

H2

(p

pm

)

H2

S (p

pm

)

H2S

H2

0

2

4

6

8

10

12

0 10 20 30 40 50 60 70 80 90 100 110 120

T2/l

im9

9 ,

SPE/

SPEl

im9

9

Time (days)

ratioT2/lim99

ratioQ/lim99

limit

Alkalinity decrease

pH decrease

Results – Pilot-scale monitoring

CH4-CO2

H2S-H2

E-nose indicators

10

Results – Pilot-scale monitoring

Scores PC1 (44.5%)

Sco

res P

C2

(2

3.8

%)

-70 -60 -50 -40 -30 -20 -10 0 10-350

-300

-250

-200

-150

-100

-50

0

50Stable pH and TAC (days 1 to 78)

Stable pH, decreasing TAC (days 78 to 98)

Decreasing TAC and pH (days 98 to 113)

day 102

days 105-106

days 109-110

days 113

Stable operation cluster

PCA monitoring Different changes in the gas phase and liquid phase are observed by the e-nose

TIC decrease

Phase II: Full-scale reactor monitoring

11

Results

12

0

1000

2000

3000

4000

5000

6000

VFA

an

d T

AN

[m

g L-

1]

Acetate

Propionate

TVFA

TAN

6.5

7

7.5

8

8.5

9

0.00

0.10

0.20

0.30

0.40

0.50

0 50 100 150 200 250 300 350 400 450 500 550 600 650

pH

VFA

/TIC

[-]

Time (days)

VFA/TIC

pH

VFA

Unknown cause CH4 CHP interruption

VFA

TAN

Results – real-scale monitoring

1 2 3 4

Signal drift decreased model perfomance

13

Results – real-scale monitoring

1 2 3 4

Adaptive model: detection of variation in process state

14

ok ok ??

Results – real-scale monitoring

1 2 3 4

1. Low gas quality and production. One engine turned off

2. VFA > 3500mg/L

3. Emptying and refilling reactor

4. VFA > 4000mg/L T-NH3> 3500 mg/L

5

15

Conclusions and Perspectives

Highlights

• Gas phase monitoring should be considered to assess anaerobic digestion reactor state

• The e-nose could detect process AD disorders by monitoring the gas phase at the pilot-scale level

• A simple indicator, derived from the complex e-nose data, summarizes reactor state

• At the real-scale level, the e-nose failed for robust monitoring of the reactor state

16

Thanks for your attention

LABORELECLABORELECLABORELEC

Biogas Rohlingerhof

L’Europe investit dans votre avenir

Projet cofinancé par l’Union Européenne via le FEDER dans le cadre du programme INTERREG IV-A Dieses Projekt wird von der EU über den EFRE-Fonds im Rahmen des Programms INTERREG IV-A kofinanziert

European Project Interreg IVa

ECOBIOGAZ (2012-2015) www.ecobiogaz.eu

OPTIBIOGAZ (2009-2012)

www.optibiogaz.eu

Acknowledgements