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Strategies for stable anaerobic digestion of vegetable waste

Strategies for stable anaerobic digestion of vegetable waste
Strategies for stable anaerobic digestion of vegetable waste
International trade and the market demand for pre-prepared agricultural produce is not only increasing the total quantity of waste agricultural biomass but also centralising its availability, making it potentially useful for energy production. The current work considers the suitability of vegetable trimmings and rejects from high-value produce air-freighted between Africa and Europe as a feedstock for anaerobic digestion. The physical and chemical characteristics of a typical mixed vegetable waste of this type were determined and the theoretical energy yield predicted and compared to experimentally-determined calorific values, and to the energy recovered through a batch biochemical methane potential test. A semi-continuous digestion trial was then carried out with daily feed additions at different organic loading rates (OLR). At an OLR of 2 g VS L?1 day?1 the substrate gave a methane yield of 0.345 L g-1 VS added with VS destruction 81.3%, and showed that 76.2% of the measured calorific value of the waste could be reclaimed as methane. This was in good agreement with the estimated energy recovery of 68.6% based on reaction stoichiometry, and was 99% of the biochemical methane potential (BMP). Higher loading rates reduced the specific methane yield and energy conversion efficiency, and led to a drop in digester pH which could not be effectively controlled by alkali additions. To maintain digester stability it was necessary to supplement with additional trace elements including tungsten, which allowed loading rates up to 4 g VS L?1 day?1 to be achieved. Stability was also improved by addition of yeast extract (YE), but the higher gas yield obtained was as a result of the contribution made by the YE and no synergy was shown. Co-digestion using card packaging and cattle slurry as co-substrates also proved to be an effective means of restoring and maintaining stable operating conditions.
anaerobic digestion, co-digestion, trace elements, vegetable waste, tungsten
0960-1481
206-214
Jiang, Y.
8637ec0f-8af3-44b9-87e6-bec78a09e9fa
Heaven, S.
f25f74b6-97bd-4a18-b33b-a63084718571
Banks, C.J.
5c6c8c4b-5b25-4e37-9058-50fa8d2e926f
Jiang, Y.
8637ec0f-8af3-44b9-87e6-bec78a09e9fa
Heaven, S.
f25f74b6-97bd-4a18-b33b-a63084718571
Banks, C.J.
5c6c8c4b-5b25-4e37-9058-50fa8d2e926f

Jiang, Y., Heaven, S. and Banks, C.J. (2012) Strategies for stable anaerobic digestion of vegetable waste. Renewable Energy, 44, 206-214. (doi:10.1016/j.renene.2012.01.012).

Record type: Article

Abstract

International trade and the market demand for pre-prepared agricultural produce is not only increasing the total quantity of waste agricultural biomass but also centralising its availability, making it potentially useful for energy production. The current work considers the suitability of vegetable trimmings and rejects from high-value produce air-freighted between Africa and Europe as a feedstock for anaerobic digestion. The physical and chemical characteristics of a typical mixed vegetable waste of this type were determined and the theoretical energy yield predicted and compared to experimentally-determined calorific values, and to the energy recovered through a batch biochemical methane potential test. A semi-continuous digestion trial was then carried out with daily feed additions at different organic loading rates (OLR). At an OLR of 2 g VS L?1 day?1 the substrate gave a methane yield of 0.345 L g-1 VS added with VS destruction 81.3%, and showed that 76.2% of the measured calorific value of the waste could be reclaimed as methane. This was in good agreement with the estimated energy recovery of 68.6% based on reaction stoichiometry, and was 99% of the biochemical methane potential (BMP). Higher loading rates reduced the specific methane yield and energy conversion efficiency, and led to a drop in digester pH which could not be effectively controlled by alkali additions. To maintain digester stability it was necessary to supplement with additional trace elements including tungsten, which allowed loading rates up to 4 g VS L?1 day?1 to be achieved. Stability was also improved by addition of yeast extract (YE), but the higher gas yield obtained was as a result of the contribution made by the YE and no synergy was shown. Co-digestion using card packaging and cattle slurry as co-substrates also proved to be an effective means of restoring and maintaining stable operating conditions.

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More information

e-pub ahead of print date: 7 February 2012
Keywords: anaerobic digestion, co-digestion, trace elements, vegetable waste, tungsten
Organisations: Centre for Environmental Science

Identifiers

Local EPrints ID: 300464
URI: http://eprints.soton.ac.uk/id/eprint/300464
ISSN: 0960-1481
PURE UUID: cf2d4ad4-98ab-4f8a-bdb2-69a2670b101a
ORCID for S. Heaven: ORCID iD orcid.org/0000-0001-7798-4683

Catalogue record

Date deposited: 22 Feb 2012 11:46
Last modified: 17 Mar 2020 01:25

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