Page 279 - Materials Chemistry, Second Edition

260 Life Cycle Assessment of Wastewater Treatment

It is important to note that several studies have adopted a large number of impact
categories, such as El-Sayed et al. (2010), Musharrafie et al. (2011), Barjoveanu et al.
(2014), and Resende et al. (2015).
The main advantage of considering several impact categories in a study is to guar-
antee that all possible impacts of the system will be investigated. On the other hand,
the workload will be proportional to the number of impact categories evaluated,
which could justify the selection of those with the greatest impact.
So, some studies preferred to focus only on one or two impact categories, such
as Limphitakphong et al. (2016), which studied wastewater systems in Thailand
addressing global warming and eutrophication, and Ledon et al. (2017), which
focused on evaluating global warming and resource consumption in wastewater sys-
tems in Chile.
According to the International Reference Life Cycle Data System (ILCD) guide
(ILCD, 2010), previous knowledge based on experience acquired from detailed stud-
ies for similar systems may indicate that one or more of the default impact categories
are not relevant for the system being analyzed. However, the elimination of impact
categories needs to be explicitly justified, as it could directly affect the conclusions
of the study. So, in the absence of a previous study that could support the selection
of some impact categories, the adoption of several categories is encouraged. In the
case of developing countries, as previous studies are scarce, there is a low chance of
finding similar studies that could support the elimination of impact categories. So,
an important aspect for future research in these countries is to study the influence of
each impact category on the overall impact of the system.

12.4.10 norMalizaTion proceDures
According to Stranddorf et al. (2005), the goal of normalization is to relate the impact
scores to a common reference to enable the comparison of different environmental
impacts. From ISO guidelines, normalization is an optional step of life cycle impact
assessment (LCIA), which allows results to be presented after the characterization
step using a common reference impact (Benini et al., 2014). The review results show
that 39% of papers included the normalization step in the LCA study.
The predominance of papers that do not adopt normalization is probably related to
the uncertainty involved in the normalization factors, which express the total impact
occurring in a reference region for a certain impact category within a reference year
(Benini et al., 2014). It is important to note that the determination of normalization
factors is a very challenging task, which demands significant effort and time as well
as an intimate knowledge of data availability and quality (Kim et al., 2013). As
normalization factors vary from region to region, and for most developing countries
there is no specific data for their regions, normalization is not recommended without
the development of regional factors.

12.4.11 sensiTiviTy analysis
According to Figure 12.7, only 28% of studies presented a step involving sensitivity
analysis. So, although it is an important step in LCA, it was observed that the huge