Co-digestion at WWTPs for energy

self-sufficiency: Opportunities and

challenges

Sihuang Xie & Long NghiemSchool of Civil, Mining and Environmental Engineering, University of

Wollongong

Philip Woods, Brendan Galway & Heriberto

BustamanteSydney Water

21th November 2017Bioenergy Australia Conference 2017

Outline

Drivers & challenges

Anaerobic co-digestion of sewage sludge &

beverage waste at Shellharbour WWTP

Conclusions

Australia’s largest water and wastewater

service provider

A period of

unprecedented

capital investment

BioenergyDrivers

Reduce the impact energy on customer bills

Be a high productivity business

Contribute to the state targets for carbon emissions and

waste reduction

Challenges

Integrating regulated & non-regulated business streams

What business are we and what might we be in the future?– wastewater manager or waste manager?

– water & wastewater service or resource recovery business?

– energy user or future energy generator?

Food wasteWork Plan

Three parts:

Full scale trials (existing capacity)– Bondi

– Cronulla

Research– Shellharbour

Commercialise (expanded capacity)– St Marys

ARC Linkage Project (2016-2018)

A: co-digestion B: control

Analytics to predict anaerobic co-digestion & downstream process performance

Anaerobic digester

SCADA

Multidisciplinary approaches

Pilot co-digestion system design

The only one of itskind

Two-stage AcoD

SCADA systemwith remote controlcapacity

Co-digestion evaluation

Co-digestion (A) &control digester (B)

Feed stoichiometry

Downstreamprocess efficiency

Offline Monitoring

Biogas quality:CH4, CO2, H2S

Biosolids odour:H2S, CH4S,(CH3)2S

Process engineering Molecular biology Analytical chemistry

Predictive analytics decision making tool

17-Aug 21-Aug 25-Aug 29-Aug 2-Sep 6-Sep 10-Sep 14-Sep

100

200

300

400

500

600

700Beer/premixed drink

Co-digestion reactor

Control reactor

Bio

gas p

roduction (

L/d

)

Date

Diet coke

Results: co-digestion

Biogas production from digester A (fed with 90% sewage sludge and 10%

beverage waste) and digester B (fed with 100% sewage sludge).

22 Mar

5 Apr

19 Apr

3 May

17 May

31 May

14 Jun1 A

ug

15 Aug

29 Aug

12 Sep

26 Sep

10 Oct

24 Oct

0

100

200

300

400

500

600

700

Daily

bio

ga

s p

rod

uction

(L/d

)

Date

Digester A

Digester B

Results: bioenergy production

• Biomethane potential of beverage waste (except wine) is >4 times higher than

that in sewage sludge on a volume basis

• Synergistic effects (increase in specific methane yield or process kinetics) are

yet to be evaluated during co-digestion beverage waste with sewage sludge

Results: inhibition

Daily biogas production during inhibitory co-digestion stage

Mar 28Apr 3

Apr 9

Apr 15

Apr 21

Apr 27May 3

May 9

May 15

May 21

May 27Jun 2

Jun 8

Jun 14

Jun 20

0

100

200

300

400

500

600

Da

ily B

iogas p

roduction (

L/d

)

Date

Digester A

Digester B

Co-digestion of beer commenced from 29 March – 9 April, followed by a number

of technical issues resulting in low or no biogas production in both digesters until

30 April

Co-digestion of beer commenced from 10 May - 21 May

Co-digestion of wine commenced from 26 May - 11 June

Both system fed with raw sludge from 12 June - 18 June

Co-digestion

(wine)

Inhibitory stage Co-digestion

(beer)

Mono-

digestion

Co-digestion

(beer)

Bisolids odour

H2S: <800 ppm >3000 ppm

(CH3)2S: <10 ppm >150 ppm

Biogas quality

H2S: <1500 ppm >4000 ppm

CH4: >60% <35%

Inhibitory substances

Sulphur compounds, alcohols

and phenolic compounds

10 Jan

31 Jan

21 Feb

14 Mar

4 Apr

25 Apr

16 May

6 Jun

27 Jun18 Jul

8 Aug

29 Aug

19 Sep

10 Oct

31 Oct

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Digester A

Digester B

Sewage sludge

To

tal so

lid (

%)

Date10 Jan

31 Jan

21 Feb

14 Mar

4 Apr

25 Apr

16 May

6 Jun

27 Jun18 Jul

8 Aug

29 Aug

19 Sep

10 Oct

31 Oct

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0Digester A

Digester B

Sewage sludge

Vo

latile

so

lid (

%)

Date

• Along with biogas & biosolids odorous emissions, digestate

dewaterability can be worsened due to the inhibitory effects

Results: microbial community

Digester BDigester A

Co-digestion

(beer)Recovery

AcoD

(beer)

AcoD

(wine)

• Co-digestion reduces the diversity of microbial community

• Overdosing of some co-substrate can inhibit methanogen

Conclusions

➢ Pilot co-digestion evaluation with beverage waste at 10% (v/v)

shows an increase of >40% in bioenergy production compared

to mono-digestion

➢ Co-digestion can reduce the diversity of microbial community.

Digesters resilience can be reduced when wine waste is used.

➢ Biogas and biosolids quality were not adversely affected during

stable operation of AcoD systems

➢ Further results of this project can be used to establish

commercial parameters for co-digestion of food waste at

WWTPs

This research was supported under ARC LP funding scheme and by

Sydney Water

Garry Arblaster and his colleagues at Shellharbour WWTP

Acknowledgements

UOW team:

Hop Phan, Richard Wickham,

Tian Xie, Truong Vu, Quynh

Nguyen, Ashley Ansari

Thank you for your attention!