Page 72 - Materials Chemistry, Second Edition

58 N. E. Korres

GHG emissions due to irrigation can be calculated based on the following
equation (Eq. 7):
Q EF
GHG emissions kg CO eð 2 Þ ¼ ð7Þ
1000
where Q (activity) is the electricity used expressed in kWh and EF is the relevant
emission factor expressed in kg CO 2 e/kWh. With respect to lignite power plants,
significant variations in cumulative GHG emissions have been quoted in the lit-
erature, ranging from approx. 800–1,700 g CO 2 e q/kWh e (Weisser 2007). The
great variation in the emissions of current lignite power plants indicates the
importance of thermal plant efficiency and operating mode, since most GHG
emissions occur at the combustion stage (Weisser 2007).

Allocation

Agricultural LCA is often complex because in addition to the main product there
are usually coproducts, so that appropriate environmental impacts need to be
assigned to each product, a process known as allocation. There may also be by-
products or waste and emissions to the environment, for example, nitrate (NO 3 )to
water and nitrous oxide (N 2 O) to the air (Harris and Narayanaswamy 2009).
Allocation may be performed on a mass, volume, economic, or energy basis
although it is best to avoid allocation through system expansion or division of
processes into product-specific subprocesses (Vikman et al 2004; Labutong et al.
2012) Economic allocation has, in the past, been utilized but studies of beef and
dairy products have shown this to increase uncertainty. The need for allocation can
be dependent on choice of FU and system boundary. Allocation was not needed in
one beef study because the FU choice (live weight) and system boundary (cradle-
to-farm gate) meant that the by-products occurred outside the farm gate (by-
products occur post-processing). Karlsson (2003) estimated GHG emissions and
mitigation costs for a range of biomass-based cogeneration systems under different
methodological assumptions. The choice of a FU was given strong consideration,
since the proportion between the products may differ between the studied and the
reference system (i.e., an alternative, typically a ‘‘job as usual’’, system with which
the system under examination is compared). This can be dealt with by considering
one product as the FU and the other as a by-product and then assuming that the
difference in generation of the by-product is balanced by another energy system in
the reference scenario (allocation by subtraction) (Vikman et al 2004).

4.3 Environmental Impact Assessment

The life cycle impact assessment (LCIA) phase of an LCA is the evaluation of
potential human health and environmental impacts of the environmental resources
and releases identified during the LCI. Impact assessment should address eco-
logical effects and human health effects; it may also address resource depletion.