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Relationships between the composition of sludge and performance of anaerobic digesters Patrick Lee, PhD Assistant Professor School of Energy and Environment City University of Hong Kong 11 November 2015 DSD R&D Forum 2015, Session 1:

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Relationships between the composition of sludge and performance of anaerobic digesters

Patrick Lee, PhD Assistant Professor School of Energy and Environment City University of Hong Kong 11 November 2015

DSD R&D Forum 2015, Session 1: Wastewater Management

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An importance source of renewable energy

Bioenergy generation and projection by region

International Energy Agency (2013)

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3 http://www.scielo.br/img/revistas/ambiagua/v9n2/a02fig01.jpg

http://newenergynews.blogspot.hk/2012/06/quick-news-june-26-first-solar-plant-ok.html

  • A growing trend

worldwide to utilize biogas

  • An important source of

renewable energy

Production

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Feedstocks: Wastewater and sludge

China:

In 2012, generated >68.5 billion metric tons of wastewater; by 2015 expected to rise to 78.4 billion metric tons

The amount of sewage sludge would increase accordingly, from 30 million metric tons (at a moisture content of 80%) in 2012 to 34 million metric tons in 2015

Ref: Feng et al, ES&T, 2015

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Feedstocks: Wastewater and sludge

USA:

In 2014, 14,780 municipal WWTP, treating an average wastewater flow of 3,785m3/day

About 6.5 million metric tons (dry weight)

  • f sewage sludge are generated annually

Municipal wastewater treatment accounts ~3 to 4% of USA’s electrical demand, adding 21 million metric tons of GHG emission

Ref: Shen et al, Renew Sust Energ Rev, 2015

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Energy content in wastewater and sludge

Ref: Shen et al, Renew Sust Energ Rev, 2015

  • 1MGD wastewater equates 26 kW of electric capacity
  • Sludge energy content = 8000 Btu/dry lb
  • Enough to support ~0.5% of USA total energy

consumption per year

  • Going from net consumer to producer
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AD operation in WWTPs in USA

Ref: Shen et al, Renew Sust Energ Rev, 2015

Operating temperature Biogas utilization CHP technologies

92% mesophilic 70% utilized ~23% applied

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Utilization consideration: Wastewater and sludge

Feedstocks Usage for AD Primary & secondary sludge from WWTP

Organic waste (e.g. agriculture waste, manure, food waste)

High-strength industrial wastewater

Low-strength municipal wastewater

?

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AD of municipal wastewater

Challenges:

Low organic concentrations (500 mg COD/L)

Low temperature

Retaining biomass

May not yield effluent that meets discharge standard (require extra polishing) Demonstration:

Anaerobic fluidized membrane reactor with GAC as support

Achieved 99% removal of COD

< 1 mg/L of suspended solids

It’s possible but not conventional aerobic systems

Ref: McCarty et al, ES&T, 2015

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AD of municipal wastewater: Benefits

Methane yield: Enhanced Sludge yield: Reduced Energy yield: Enhanced

Ref: McCarty et al, ES&T, 2015

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Research need: In order to increase efficiency, reliability and robustness of AD, need to understand the microorganisms (or the engines) that drive the process in conjunction with engineering process design

Going forward

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?

Biological, physical, chemical complexity

Anaerobic digestion: A black box

Waste CH4

Engineering

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Metabolic interactions

Anaerobic digestion Substrate A

CH4

Process and microbiology are coupled

Ref: Sales and Lee, Curr. Opin. Biotechnol., 2015

Dilemma

Microorganisms affect the process The process affects the microorganisms

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Metabolic interactions

Anaerobic digestion Substrate A

CH4

Process and microbiology are coupled

Ref: Sales and Lee, Curr. Opin. Biotechnol., 2015

Dilemma

Microorganisms affect the process The process affects the microorganisms

A dynamic system

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Metabolic interactions

Anaerobic digestion Substrate A

CH4

Process and microbiology are coupled

Ref: Sales and Lee, Curr. Opin. Biotechnol., 2015

Dilemma

Microorganisms affect the process The process affects the microorganisms #1 #2 #3 #4

Conc Time

Performance?

A dynamic system

Fluctuate High/Low Stable Occasionally high

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Practical question #1

Seed #1 Seed #2 Seed #3

Same Influent Performance: the same, better or crash?

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Practical question #2

Influent “A” If suddenly switch to Influent “B”, performance the same, better or crash?

Initially

Influent “B”

At a later time Seed #1 Seed #2 Seed #3

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Question?

Ref: http://angieaway.com/wp-content/uploads/2013/03/532968_10102270976272161_2033021876_n.jpg

All roads lead to Rome? That is, will the microbes find a way?

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Practical question #1

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Practical question #1

Seed #1 Seed #2 Seed #3

Same Influent Performance: The same or different

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Cellulose, cellulose (55oC), xylan, xylose, foodwaste Function (i.e. methane yield), microbial community composition

???

Substrate tested: Outcome:

Practical question #1

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Methane yield

 Similar methane yield between the two seeds with the five

tested substrates

Ref: Wilkins and Lee et al, Front Microbiol, 2015

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Clustering

Archaea Bacteria

Ref: Wilkins and Lee et al, Front Microbiol, 2015

 No strong clustering of

the microorganisms based on substrate

 That is, each seed used

a different population to digest the same substrate

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Relative abundance of phyla

(a) Archaeal orders (b) Bacterial phyla

Wilkins and Lee et al, Front. Microbiol., 2015

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Practical question #1

Seed #1 Seed #2 Seed #3

Same Influent

Summary: Different seeds, different populations, similar functions. “Does seem more than one road leads to Rome”

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Practical question #2

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Practical question #2

Influent “A” If suddenly switch to Influent “B”, Performance the same, better or crash?

Initially

Influent “B”

At a later time Seed #1 Seed #2 Seed #3

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 Seed samples collected from two AD systems

 Day-to-day not treating cellulose and xylan  Fed with cellulose and xylan

X

Practical question #2

Lee et al, Unpublished data

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  • 5

5 10 15 20 25 30 35 40

CH4 (mL) Duration (days)

A

5 10 15 20 25 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

pH Duration (days)

SWH-C-55 GZ-C-35 SWH-C-35 GZ-X-35 SWH-X-35

B

5 10 15 20 25 5 10 15 20 25 30 35

  • Conc. of acetic acid (mM)

Duration (days)

C

5 10 15 20 25 1 2 3 4 5 6

  • Conc. of cellulose or xylan (g/L)

Duration (days)

D

No significant differences in performance regardless of the origin of the seeds

Xylan Cellulose

Performance

Capable to digest cellulose and xylan CH4 produced Except 55oC

Lee et al, Unpublished data

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Seed vs. Seed

  • The two seeds are

different

Lee et al, Unpublished data

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Seed vs. Enrichment

  • The selected microorganisms are different from the seed

Xylan Cellulose Xylan Cellulose SWH GZ

Before Before Before Before After After After After

Lee et al, Unpublished data

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The correct microbes are present

  • The selected microorganisms have the correct functions

Lee et al, Unpublished data

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Practical question #2

Influent “A”

Initially

Influent “B”

At a later time Seed #1 Seed #2 Seed #3

Summary: Can select if small quantity of the right microorganisms are in the seed, but absent in the first place (e.g. 55oC) then nothing will happen

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Global trend

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Many plants worldwide

Operating AD in the UK

http://www.biogas-info.co.uk/resources/biogas-map/

Operating AD in Poland

http://biogazownierolnicze.pl/mapa-biogazowni

Operating AD in the USA

https://www.americanbiogascouncil.org/biogas_maps.asp

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Many plants worldwide

Operating AD in the UK

http://www.biogas-info.co.uk/resources/biogas-map/

Operating AD in Poland

http://biogazownierolnicze.pl/mapa-biogazowni

Operating AD in the USA

https://www.americanbiogascouncil.org/biogas_maps.asp

Realistically, the microorganisms in all these systems CANNOT be IDENTICAL, due to differences in the influent, operating conditions (temperature, retention time, etc). At the same time, they CANNOT be all DIFFERENT, otherwise AD is not AD.

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Many plants worldwide

Operating AD in the UK

http://www.biogas-info.co.uk/resources/biogas-map/

Operating AD in Poland

http://biogazownierolnicze.pl/mapa-biogazowni

Operating AD in the USA

https://www.americanbiogascouncil.org/biogas_maps.asp

Core Shared Shared Unique Unique Unique Unique Shared Shared Shared Shared Shared Shared

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Analyzed 4 full-scale anaerobic digesters

Sludge HK Wastewater China

Ref: Wilkins and Lee et al, AEM, 2015

Focused on the methane-generating organisms

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There are differences between the digesters

 The freshwater sludge digesters were closely clustered and

separated from the saline sludge and wastewater digesters mcrA 16S

Ref: Wilkins and Lee et al, AEM, 2015

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Acetoclastic Acetoclastic Hydrogenotrophic Hydrogenotrophic Hydrogenotrophic “Methanogen” “Methanogen”

mcrA 16S

The major methane-generating organisms are present; methane are produced in all systems

Ref: Wilkins and Lee et al, AEM, 2015

There are similarities between the digesters

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Conclusions

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Implications:

1.) AD is vital to urbanized cities, an important source of renewable energy and for waste treatment 2.) Reliability and robustness of the process should increase as we look deeper inside the black box

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?

Biological, physical, chemical complexity

Anaerobic digestion: A black box

Waste CH4

Engineering

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?

Biological, physical, chemical complexity

Anaerobic digestion: A black box

We have the tools to look inside the blackbox

Waste CH4

Engineering

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Implications:

1.) AD is vital to urbanized cities, an important source of renewable energy and for waste treatment 2.) Reliability and robustness of the process should increase as we look deeper inside the black box 3.) Operation of the systems and the microorganisms are coupled in a deterministic fashion (i.e. can be explained, there is a reason)

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Many plants worldwide

Operating AD in the UK

http://www.biogas-info.co.uk/resources/biogas-map/

Operating AD in Poland

http://biogazownierolnicze.pl/mapa-biogazowni

Operating AD in the USA

https://www.americanbiogascouncil.org/biogas_maps.asp

Core Shared Shared Unique Unique Unique Unique Shared Shared Shared Shared Shared Shared

Manipulations

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A relevant example

SCMP, 6 Oct 2015

http://www.scmp.com/news/hong-kong/health-environment/article/1864529/faecal-extract-transplants-three-times-more http://hk.apple.nextmedia.com/news/art/20150717/19222723

http://i.kinja-img.com/gawker-media/image/upload/s--c7OT9sRj--/c_fit,fl_progressive,q_80,w_636/180b07i84w139jpg.jpg
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Anaerobic digestion Substrate A

CH4

Process and microbiology are coupled

Ref: Sales and Lee, Curr. Opin. Biotechnol., 2015

Dilemma

Microorganisms affect the process The process affects the microorganisms

If the relevant microorganisms are NOT there, can add If the relevant microorganisms are there, can ENGINEER the process A dynamic system

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Questions?

Email: patrick.kh.lee@cityu.edu.hk