Volume 175, 15 June 2016, Pages 20–32
Research article
- a Biomass, Bioproducts and Energy Unit, Walloon Agricultural Research Centre (CRA-W), 146 chaussée de Namur, 5030 Gembloux, Belgium
- b Farming Systems, Territory and Information Technologies Unit, CRA-W, 100 rue du Serpont, 6800 Libramont, Belgium
- c Animal Breeding, Quality Production and Welfare Unit, CRA-W, 8 rue de Liroux, 5300 Gembloux, Belgium
- d Crop Production Systems Unit, CRA-W, 4 rue du Bordia, 5030 Gembloux, Belgium
- Received 27 October 2015, Revised 3 March 2016, Accepted 14 March 2016, Available online 25 March 2016
Highlights
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- We conducted a consequential LCA (cLCA) of a farm-scale biogas plant.
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- We discussed assumptions on processes displaced by co-product and input uses.
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- Identifying the marginal electricity production technology is decisive.
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- Digestate use displaces fertilizers but induces acidification and eutrophication.
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- Biogas plants should not be fed with by-products previously used in animal feed.
Abstract
Producing
biogas via anaerobic digestion is a promising technology for meeting
European and regional goals on energy production from renewable sources.
It offers interesting opportunities for the agricultural sector,
allowing waste and by-products to be converted into bioenergy and
bio-based materials. A consequential life cycle assessment (cLCA) was
conducted to examine the consequences of the installation of a
farm-scale biogas plant, taking account of assumptions about processes
displaced by biogas plant co-products (power, heat and digestate) and
the uses of the biogas plant feedstock prior to plant installation.
Inventory
data were collected on an existing farm-scale biogas plant. The plant
inputs are maize cultivated for energy, solid cattle manure and various
by-products from surrounding agro-food industries. Based on hypotheses
about displaced electricity production (oil or gas) and the initial uses
of the plant feedstock (animal feed, compost or incineration), six
scenarios were analyzed and compared. Digested feedstock previously used
in animal feed was replaced with other feed ingredients in equivalent
feed diets, designed to take account of various nutritional parameters
for bovine feeding. The displaced production of mineral fertilizers and
field emissions due to the use of digestate as organic fertilizer was
balanced against the avoided use of manure and compost.
For
all of the envisaged scenarios, the installation of the biogas plant
led to reduced impacts on water depletion and aquatic ecotoxicity
(thanks mainly to the displaced mineral fertilizer production). However,
with the additional animal feed ingredients required to replace
digested feedstock in the bovine diets, extra agricultural land was
needed in all scenarios. Field emissions from the digestate used as
organic fertilizer also had a significant impact on acidification and
eutrophication.
The choice of displaced marginal
technologies has a huge influence on the results, as have the
assumptions about the previous uses of the biogas plant inputs. The main
finding emerging from this study was that the biogas plant should not
use feedstock that is intended for animal feed because their replacement
in animal diets involves additional impacts mostly in terms of extra
agricultural land. cLCA appears to be a useful instrument for giving
decision-makers information on the consequences of introducing new
multifunctional systems such as farm-scale biogas plants, provided that
the study uses specific local data and identifies displaced reference
systems on a case-by-case basis.
Keywords
- Consequential life cycle assessment;
- Biogas plant;
- Anaerobic digestion;
- Co-product;
- Animal feed;
- Local data
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