Page 99 - Materials Chemistry, Second Edition

Life-Cycle Assessment of Biomethane 85

300
250
Energy (GJ ha -1 a -1 ) 150
200

100
50
0
Rapeseed Wheat Palm oil Sugarcane Grass
biodiesel ethanol biodiesel ethanol biomethane
Net energy 25 4 74 120 69
Gross 46 66 120 135 122
energy
Fig. 2 The net and gross energy of different biofuels systems (Korres et al. 2010, 2011; Smyth
et al. 2009)

less gross and net energy in comparison with palm oil biodiesel, grass biomethane,
and sugarcane bioethanol (Fig. 2). The option to import substrates for biodiesel
production from tropical countries, such as Indonesia and Malaysia, is not a viable
option as they result in a high demand for the production of palm oil, which is 80 %
of the global production (Korres et al. 2011). Consequently, deforestation is
occurring at an annual rate of 1.5 % (Fargione et al. 2008). There are no net GHG
emission savings with a change in land use (Reinhard and Zah 2009). According to
Directive 2009/28/EC, palm oil biodiesel is not considered as biofuel because it
needs to achieve GHG savings of 60 % by 2020 (EC 2009). The increase in palm oil
production causes habitat loss, drainage of peatlands, and land conflicts (Colchester
et al. 2006). Similar issues of deforestation, decarbonization, and soil degradation
occur with the production of sugarcane ethanol (Goldemberg et al. 2008).
According to Korres et al. (2010, 2011), biofuel in form of enriched biomethane
produced from lignocellulosic biomass like grass silage is much better for Europe
than rape seed biodiesel and wheat ethanol (Fig. 2). The low-input indigenous
perennial grasses provide biofuel with more useable energy, GHG savings and less
pollution related to agrochemical procedures than arable crops per hectare. The
arable crops can be corn grain ethanol or soybean biodiesel (Tilman et al. 2006;
Korres et al. 2011). The benefits of producing biomethane as a transport fuel from
lignocellulosic biomass through the AD process are shown in Fig. 3.

3.2 GHG Emissions

Korres et al. (2010) assessed the GHG emissions of enriched biomethane as a
transport biofuel produced by grass silage in place of diesel as
-1
69.74 g CO 2 eq. MJ -1 energy replaced or 6,904 kg CO 2 eq. ha -1 yr . This was