The University of Southampton
University of Southampton Institutional Repository

The suitability of anaerobic digesters on organic farms

The suitability of anaerobic digesters on organic farms
The suitability of anaerobic digesters on organic farms
Food and energy security are two key environmental challenges currently faced by mankind. The principles behind organic farming are to promote environmental sustainability; however within the organic standards the use of renewable energy is only a suggested method with which to achieve this. If organic farmers can successfully utilise anaerobic digesters, they could contribute towards the provision of both food and energy security using one holistic system. Within this thesis, the suitability of anaerobic digesters on organic farms was explored using methods from ecological, sociological and environmental sciences. This enabled both the practical and theoretical issues behind the question of whether it is suitable for anaerobic digesters to be used on organic farms to be addressed.

Field and laboratory experiments were used to compare the effects digestate and slurry had on earthworms, grass and weeds. Digestate and slurry had species dependent effects on earthworms during both LD50 / LT50 experiments and behavioural bioassays; Lumbricus terrestris survived longer in slurry and showed a behavioural preference towards slurry over digestate, whereas Eisenia fetida showed the opposite responses. Fertiliser application rates over 170 kg N ha-1 were found to be harmful to both species of earthworm. Suppressed germination effects were seen on thistles treated with digestate compared with no treatment (F0.56,19.66 =4.66, P < 0.01), whilst grass fertilised with digestate had a greater total mass than grass fertilised with slurry or left unfertilised (F2,27 =17.92, P < 0.001).
Questionnaires and interviews were used to obtain a better understanding of the opinions farmers had about anaerobic digesters. Organic farmers believed renewable energy generation fitted well within organic principles, but using an anaerobic digester on an organic farm was less practical than on a conventional farm. This was due to multiple reasons including lack of information, poor associated finances, and that existing digesters are currently unsuitable for small organic farms. There was also support for anaerobic digesters to be on dairy farms- this was regardless of whether the farm was organic or conventional.

Two case-study farms were used to assess the impact an anaerobic digester would have on the farms total GHG emissions. An anaerobic digester on the dairy farm was calculated to reduce GHG emissions by up to 24%, while for the mixed farm, the maximum reduction was by 20%. This was primarily due to the fact that the dairy farm benefitted from a higher volume of feedstock and proposed to use the biogas in a more energy efficient manner by producing electricity rather than vehicle fuel. Due to the high emissions associated with keeping livestock, both case studies needed to import additional feedstock if the farms were to achieve zero net GHG emissions.

The answer to whether anaerobic digesters can be suitable for organic farms was judged on how well they complimented or conflicted with IFOAM’s definition of organic farming. Three main aspects of their definition were chosen and evidence from each chapter used to address the main question of the thesis. In conclusion, anaerobic digesters are theoretically suitable for use on organic farms, but are generally more practical for use on conventional farm systems. Across both farm systems the most suitable enterprises to adopt anaerobic digesters are dairy farms. This highlights the need for suitability of new systems to be assessed on a case-by-case scenario when trying to maximise positive impacts from new technologies.
Clements, Laura
27e69f8b-2045-40ad-95bd-4b29aa26731c
Clements, Laura
27e69f8b-2045-40ad-95bd-4b29aa26731c
Poppy, Guy
e18524cf-10ae-4ab4-b50c-e73e7d841389

Clements, Laura (2012) The suitability of anaerobic digesters on organic farms. University of Southampton, Biological Sciences, Doctoral Thesis, 243pp.

Record type: Thesis (Doctoral)

Abstract

Food and energy security are two key environmental challenges currently faced by mankind. The principles behind organic farming are to promote environmental sustainability; however within the organic standards the use of renewable energy is only a suggested method with which to achieve this. If organic farmers can successfully utilise anaerobic digesters, they could contribute towards the provision of both food and energy security using one holistic system. Within this thesis, the suitability of anaerobic digesters on organic farms was explored using methods from ecological, sociological and environmental sciences. This enabled both the practical and theoretical issues behind the question of whether it is suitable for anaerobic digesters to be used on organic farms to be addressed.

Field and laboratory experiments were used to compare the effects digestate and slurry had on earthworms, grass and weeds. Digestate and slurry had species dependent effects on earthworms during both LD50 / LT50 experiments and behavioural bioassays; Lumbricus terrestris survived longer in slurry and showed a behavioural preference towards slurry over digestate, whereas Eisenia fetida showed the opposite responses. Fertiliser application rates over 170 kg N ha-1 were found to be harmful to both species of earthworm. Suppressed germination effects were seen on thistles treated with digestate compared with no treatment (F0.56,19.66 =4.66, P < 0.01), whilst grass fertilised with digestate had a greater total mass than grass fertilised with slurry or left unfertilised (F2,27 =17.92, P < 0.001).
Questionnaires and interviews were used to obtain a better understanding of the opinions farmers had about anaerobic digesters. Organic farmers believed renewable energy generation fitted well within organic principles, but using an anaerobic digester on an organic farm was less practical than on a conventional farm. This was due to multiple reasons including lack of information, poor associated finances, and that existing digesters are currently unsuitable for small organic farms. There was also support for anaerobic digesters to be on dairy farms- this was regardless of whether the farm was organic or conventional.

Two case-study farms were used to assess the impact an anaerobic digester would have on the farms total GHG emissions. An anaerobic digester on the dairy farm was calculated to reduce GHG emissions by up to 24%, while for the mixed farm, the maximum reduction was by 20%. This was primarily due to the fact that the dairy farm benefitted from a higher volume of feedstock and proposed to use the biogas in a more energy efficient manner by producing electricity rather than vehicle fuel. Due to the high emissions associated with keeping livestock, both case studies needed to import additional feedstock if the farms were to achieve zero net GHG emissions.

The answer to whether anaerobic digesters can be suitable for organic farms was judged on how well they complimented or conflicted with IFOAM’s definition of organic farming. Three main aspects of their definition were chosen and evidence from each chapter used to address the main question of the thesis. In conclusion, anaerobic digesters are theoretically suitable for use on organic farms, but are generally more practical for use on conventional farm systems. Across both farm systems the most suitable enterprises to adopt anaerobic digesters are dairy farms. This highlights the need for suitability of new systems to be assessed on a case-by-case scenario when trying to maximise positive impacts from new technologies.

PDF
__soton.ac.uk_ude_PersonalFiles_Users_lp5_mydocuments_Theses PDF files_LauraClements.pdf - Other
Download (2MB)

More information

Published date: 10 September 2012
Organisations: University of Southampton, Centre for Biological Sciences

Identifiers

Local EPrints ID: 354422
URI: https://eprints.soton.ac.uk/id/eprint/354422
PURE UUID: 9df140bd-41b2-4c90-b533-d0fd8c60ec9d

Catalogue record

Date deposited: 21 Oct 2013 12:55
Last modified: 18 Jul 2017 03:56

Export record

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×