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Simultaneous biomethanisation of endogenous and imported CO2 in organically loaded anaerobic digesters

Simultaneous biomethanisation of endogenous and imported CO2 in organically loaded anaerobic digesters
Simultaneous biomethanisation of endogenous and imported CO2 in organically loaded anaerobic digesters
In-situ biomethanisation reduces the CO2 in biogas to CH4 via direct H2 injection into an anaerobic digester, but volumetric methane production (VMP) is limited by organic loading. Ex-situ biomethanisation, where gaseous substrates are fed to pure or mixed cultures of hydrogenotrophic methanogens, offers higher VMP but requires an additional reactor and supply of essential nutrients. This work combined the two approaches in a novel hybrid application achieving simultaneous in-situ and ex-situ biomethanisation within an organically-loaded anaerobic digester receiving supplementary biogas. Conventional stirred-tank digesters were first acclimated to H2 addition, increasing biogas methane content from 50% to 95% and VMP from 0.86 to 1.51 L L-1 day-1 at a moderate loading rate of 3 g organic chemical oxygen demand per L per day (g CODorg L-1 day-1). Externally-produced biogas was then added to demonstrate simultaneous biomethanisation of endogenous and imported CO2. This further increased VMP to 2.76 L L-1 day-1 without affecting organic substrate degradation. In-situ CO2 reduction can alter digester pH by reducing bicarbonate buffering: the combined process operated stably at around pH 8.0 with 3-5% CO2 in the headspace. Microbial community analysis indicated the process was mediated by bacterial syntrophic acetate oxidation and highly enriched hydrogenotrophic methanogenic archaea (up to 97% of the archaeal population). This approach presents the opportunity to retrofit a single digester for H2 injection to convert and upgrade biogas from several others, minimising capital and operating costs by utilising both existing infrastructure and waste-derived feedstock nutrients for simultaneous biogas upgrading and power-to-methane.
CO2 biomethanisation, Anaerobic digestion, Biogas upgrading, Power-to-gas, Hydrogenotrophic methanogens
0306-2619
670-681
Tao, Bing
a016d442-8190-4f19-b71b-d3f7e4ce357f
Alessi, Anna
b8c92e5e-a720-42cb-8ef8-b978a9f1ee9c
Zhang, Yue
69b11d32-d555-46e4-a333-88eee4628ae7
Heaven, Sonia
f25f74b6-97bd-4a18-b33b-a63084718571
Chong, James
4e4ecdde-b11e-4efa-b40b-73f0c6f62160
Banks, Charles
5c6c8c4b-5b25-4e37-9058-50fa8d2e926f
Tao, Bing
a016d442-8190-4f19-b71b-d3f7e4ce357f
Alessi, Anna
b8c92e5e-a720-42cb-8ef8-b978a9f1ee9c
Zhang, Yue
69b11d32-d555-46e4-a333-88eee4628ae7
Heaven, Sonia
f25f74b6-97bd-4a18-b33b-a63084718571
Chong, James
4e4ecdde-b11e-4efa-b40b-73f0c6f62160
Banks, Charles
5c6c8c4b-5b25-4e37-9058-50fa8d2e926f

Tao, Bing, Alessi, Anna, Zhang, Yue, Heaven, Sonia, Chong, James and Banks, Charles (2019) Simultaneous biomethanisation of endogenous and imported CO2 in organically loaded anaerobic digesters. Applied Energy, 247, 670-681. (doi:10.1016/j.apenergy.2019.04.058).

Record type: Article

Abstract

In-situ biomethanisation reduces the CO2 in biogas to CH4 via direct H2 injection into an anaerobic digester, but volumetric methane production (VMP) is limited by organic loading. Ex-situ biomethanisation, where gaseous substrates are fed to pure or mixed cultures of hydrogenotrophic methanogens, offers higher VMP but requires an additional reactor and supply of essential nutrients. This work combined the two approaches in a novel hybrid application achieving simultaneous in-situ and ex-situ biomethanisation within an organically-loaded anaerobic digester receiving supplementary biogas. Conventional stirred-tank digesters were first acclimated to H2 addition, increasing biogas methane content from 50% to 95% and VMP from 0.86 to 1.51 L L-1 day-1 at a moderate loading rate of 3 g organic chemical oxygen demand per L per day (g CODorg L-1 day-1). Externally-produced biogas was then added to demonstrate simultaneous biomethanisation of endogenous and imported CO2. This further increased VMP to 2.76 L L-1 day-1 without affecting organic substrate degradation. In-situ CO2 reduction can alter digester pH by reducing bicarbonate buffering: the combined process operated stably at around pH 8.0 with 3-5% CO2 in the headspace. Microbial community analysis indicated the process was mediated by bacterial syntrophic acetate oxidation and highly enriched hydrogenotrophic methanogenic archaea (up to 97% of the archaeal population). This approach presents the opportunity to retrofit a single digester for H2 injection to convert and upgrade biogas from several others, minimising capital and operating costs by utilising both existing infrastructure and waste-derived feedstock nutrients for simultaneous biogas upgrading and power-to-methane.

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Accepted/In Press date: 14 April 2019
e-pub ahead of print date: 22 April 2019
Published date: 1 August 2019
Keywords: CO2 biomethanisation, Anaerobic digestion, Biogas upgrading, Power-to-gas, Hydrogenotrophic methanogens

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Local EPrints ID: 430507
URI: http://eprints.soton.ac.uk/id/eprint/430507
ISSN: 0306-2619
PURE UUID: 034551e6-200e-466c-91a1-d70d0578d3f9
ORCID for Yue Zhang: ORCID iD orcid.org/0000-0002-5068-2260
ORCID for Sonia Heaven: ORCID iD orcid.org/0000-0001-7798-4683

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Date deposited: 02 May 2019 16:30
Last modified: 07 Oct 2020 06:30

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