www.cranfield.ac.uk

Converting waste-sourced CO2 into energy by AD

Dr. Yadira Bajón Fernández

September 2017

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Why reduce CO2 emissions in the water sector?

Energy demand increased by 8.7% in 4 year (2007 - 2011)

280 ppm pre-industrial era

400 ppm in 2017

Energy sector main contributor to GHG emissions, 72%

Over 5 MtCO2e per annum

Expected increase > 110,000 t per annum

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Implementation of AD to increase renewable energy, but… Can we do more?

Biogenic CO2 in UK from WW treatment

49.3%

13.3%

24.6%

12.8% Aerobic treatment

Biogas from AD

Combustion of biogas(CHP or flares)

Incineration of sludge

Adapted from: Byrns, G., Wheatley, A., Smedley, V., 2013. Carbon dioxide releases from wastewater treatment: potential use in the UK. Proc. Inst. Civ. Eng. 166, 111–121.

Biogenic CO2 emissions UK WW treatment ca. 2 MtCO2 per annum

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The concept

Biogas CO2

CH4

Utilise the capacity of ON-SITE anaerobic processes to bioconvert CO2 to

CH4 without addition of external H2

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The concept

• 60% (v/v) CO2 30% increased methane yields (Sato & Ochi, 1994)

• Injection on first stage of a TPAD 40% CO2 uptake (Francioso et

al., 2010)

Bajón Fernández, Y., Soares, A., Koch, K., Vale, P., Cartmell, E., 2017. Bioconversion of carbon dioxide in anaerobic digesters for on-site carbon capture and biogas enhancement – A review. Critical Reviews in Environmental Science and Technology.

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Proof of concept: substrate dependant response to exogenous CO2

Food waste

Sewage sludge

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% o

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eth

ane

yie

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0 1 2 3 4 5 6 7 8 9 10Cu

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DC biogas D0.9 biogas DC CH4 D0.9 CH4

•Up to 138% > CH4 production 24 hoursfor sewage sludge

•Up to 13% > CH4 yield for food waste

% of final CH4 yield obtained in first 48 hours:

- Control ADs <40% - Test ADs > 60%

Bajón Fernández, Y., Soares, A., Villa, R., Vale, P., Cartmell, E., 2014. Carbon capture and biogas enhancement by carbon dioxide enrichment of anaerobic digesters treating sewage sludge or food waste. Bioresour. Technol. 159, 1–7.

Substrate dependant responseCRITICAL: Mechanisms of CO2 utilisation can

determine implementation

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Can we scale up?… with food waste

Test AD: 0.45 ± 0.05 m3 CH4·(kg VSfed·d)-1 to 0.56 ± 0.13 m3 CH4·(kg VSfed·d)-1

ca. 20% increase

Bajón Fernández, Y., Green, K., Schuler, K., Soares, A., Vale, P., Alibardi, L., Cartmell, E., 2015b. Biological carbon dioxide utilisation in food waste anaerobic digesters. Water Res. 87, 467–475.

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What about stability?

Increased H2 baseline

Bajón Fernández, Y., Green, K., Schuler, K., Soares, A., Vale, P., Alibardi, L., Cartmell, E., 2015b. Biological carbon dioxide utilisation in food waste anaerobic digesters. Water Res. 87, 467–475.

H2: 464 ppm RR: 11.5TVFA: 17, 235 mg/LpH: 6CH4: 35%

Increased process resilience?

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Can we scale up?… with sewage sludge

Test AD: 0.37 ± 0.1 m3 CH4·(kg VSfed·d)-1 ca. 12% increase over control (p-

value < 0.05)

Alibardi, L., Green, K., Favaro, L., Vale, P., Cartmell, E., Bajón Fernández Y., 2017. Performance and stability of sewage sludge digestion under CO2

enrichment: a pilot study. Bior. Tech. In press.

Criticality of gas to liquid reporting for comparing studies (25% solubility values)

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Can we scale up?… with sewage sludge

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H2(ppm

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CH4(%)

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ControlCH4

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ControlH2

NoCO2 inj. 3CO2 inj./week NoCO2 inj. 5CO2 inj./week

Increased H2 baseline

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VFA/Alk

IA/PA

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TestVFA/Alk

ControlVFA/Alk

NoCO2 inj. 3CO2 inj./week NoCO2 inj. 5CO2 inj./week

Increased process resilience?

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Mechanism of CO2 utilisation… literature

•Aceticlastic methanogens (70%)

CH3COOH → CH4 + CO2

•Hydrogenotrophicmethanogens (30%)

4 H2 + CO2 → CH4 + 2 H2O

Methanogenesis:

• Encouragement of hydrogenotrophic route of CH4 formation(Alimahmoodi & Mulligan, 2008)

• Homoacetogenesis (Wood-Ljungdahl pathway) + acetoclastic methanogenesis

(Bajón Fernández et al., 2014; Bajón Fernández et al., 2015; Francioso et al., 2010; Salomoni et al. 2011)

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Mechanism of CO2 utilisation… hypothesis

•Aceticlastic methanogens (70%)

CH3COOH → CH4 + CO2

•Hydrogenotrophicmethanogens (30%)

4 H2 + CO2 → CH4 + 2 H2O

Methanogenesis:

• Initial CH4 increase (24 hours) more

marked in sewage sludge

o 11-16% for food waste

o 96-138% for sewage sludge

• FW contained high ammonia

concentrations (4 g/L NH4-N )

• Aceticlastic methanogens inhibited at high

ammonia concentrations

• 20% CH4 yield increase in FW pilot

All based on hypothesis until here…

(1.8 g/L NH4-N )

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Mechanism of CO2 utilisation… FISH

Sewage sludge:• Methanosaetaceae (86.4 ± 12.1 %)• Methanobaceriaceae (11.0± 4.1 %)

Food waste:• Methanosaetaceae (4.3 ± 1.7 %)• Methanobaceriaceae (1.8 ± 0.7%)• Methanosarcina (19.4 ± 9.8%)

Final population

01000020000300004000050000600007000080000

Start of ADs Digestate ofcontrol ADs

Digestate of ADswith single CO2

injection

Digestate of ADswith periodic CO2

injection

pix

el s

um

Sample

Pixel sum (Methanosaetaceae) Pixel sum (Archaea)

46 %

80 %

Bajón Fernández, Y., Soares, A., Vale, P., Koch, K., Masse, A. L., Cartmell, E., Enhancing the anaerobic digestion process through carbon dioxide enrichment: Mechanisms of utilisation. In preparation

batch

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Mechanism of CO2 utilisation… FISH

Hindered diffusion against ammonia

inhibition

Bigger Methanosarcina clusters

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Mechanisms of CO2 utilisation … so far

• limited probe permeation• Cannot fully elucidate pathway with microbial analysis

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Mechanisms of CO2 utilisation … working on

stable carbon isotopes

in ‰Delta-notation:

c

?

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Mechanisms of CO2 utilisation … stable carbon

isotopes

• Stable carbon isotope signature of biogas (𝛿13CCH4 and𝛿13CCO2) to reconstruct metabolic pathway

• Isotopically labelled substances for underlying mechanism behind CH4

increase after CO2 injection

Microbial analysis

CH313COOH

13CH3COOH

13CO2

𝛿13Cacetate

𝛿13CCH4 and𝛿13CCO2

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Some main conclusions

• Boost CH4 formation without additional H2

• Reported ranges highly variable (13%-138%): Need to report mass transfer conditions

• Substrate dependant response -> critical mechanism understanding

• Proposed mechanism: Wood-Ljungdahl pathway + acetoclastic methanogenesis

• Mechanisms elucidation in progress!

• CO2 injection can have positive impact in process stability: e.g. temperature drop, temporary overloads

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www.cranfield.ac.uk

With gratitude…