Page 97 - Materials Chemistry, Second Edition

Life-Cycle Assessment of Biomethane 83

Ploughing (machinery and Soil C-N)
Rolling/harrowing (machinery)
Lime (manufacture) Ground preparation
Lime application (machinery)

Seed (production)
Sowing
Sowing (machinery)
phase
Fertilizer (manufacture) Establishment and
Fertilizer (machinery) maintenance
Raw material production
Mowing (machinery)
Harvesting (2 cuts)
Collecting (machinery)
Fossil fuel Transport / storage

Electricity Macerating
Heat
Electricity Anaerobic digestion
Cleaning + upgrading
Electricity Compression
phase
Distribution/pumping
Fuel (digestate usage) Transport
Biomethane production
Fig. 1 A flow chart of lignocellulosic biomethane production system

emission reductions of carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and CH 4 in the
global-warming potential (GWP) with relation to fossil fuel replacement (Korres
et al. 2011). According to Gerin et al. (2008), there should be a net reduction and
gain in GHG emissions and bioenergy, respectively, in LCA studies of biomethane
produced from lignocellulosic biomass. In Figure 1, a comprehensive presentation
of the whole cycle of lignocellulosic biomethane is shown, where GHG emissions
are calculated based on energy inputs and outputs.

2.2 Goal, Scope, and Functional Unit

As a first step in conducting an LCA, goal, scope, and functional unit are defined.
The goal addresses the intended applications to the intended audience, while scope
has to be compatible with the goal of study and well defined (Singh et al. 2010a).
The functional unit is an element of the product or system, which must be mea-
surable and definable. It is used as a quantitative tool for the comparative analysis
of bioenergy systems (Casey and Holden 2005). In AD, biomethane is the main
3
product, and thus, the functional unit is described in m biomethane per year.