Page 55 - Materials Chemistry, Second Edition

36 Life Cycle Assessment of Wastewater Treatment

mask the real impacts. Other major elements that may or may not be included in
the system boundaries are impacts that it is possible to avoid. An example of this
is within the particular situation of agricultural application of treated sludge, which
allows the positive effects of the nutrient value of the sludge to be taken into account
and the system to be expanded to include the avoidance of production of synthetic
fertilizers as well as the negative consequences related to their application to soil in
terms of eutrophication and toxicity impacts.

3.2.2 life cycle inventory analySiS
The LCI involves data collection and calculation procedures to estimate the con-
sumption of resources and the qualities of waste flows and emissions attributable to
the life cycle of a product/process (ISO, 2006a). It usually starts by constructing a
flowchart of the process, representative of the goal and scope considered, and con-
tinues with data collection. Within this phase, the major concern is often related to
data availability and quality. When it comes to assessing the potential benefits of
innovative solutions, it is foreseen that data collection will come from laboratory
experiments and in the best cases, from pilot facilities. Only when well-established
technologies have been assessed can field measurements and data from real plants
be handled.
The option of modeling and simulation of a new facility, the use of a detailed
design project, and relevant literature may be useful alternatives for primary data
collection, but they are considered complementary. Background information (e.g.,
electricity generation systems, concrete and chemicals production processes) is
normally provided by LCI databases, for example the Ecoinvent (www.ecoin-
vent.ch). It is also an iterative process, because as data collection proceeds, more
information becomes available, and the goal and scope of the study might change
accordingly.

3.2.3 life cycle impact aSSeSSment
The evaluations of the potential environmental impacts associated with inventory
data are performed in the LCIA. This stage converts the potential contributions
of the resource extractions and wastes/emissions of the inventory into a number of
potential impacts. For this purpose, the ISO standards define three mandatory stages
(1 to 3) plus two optional ones (4 and 5) depicted in Figure 3.3 and are as follows:

1. Selection of impact categories, which can be classified as midpoint impact
categories (climate change, ozone layer depletion, eutrophication, ecotoxic-
ity, human toxicity, resource depletion, land use, acidification, radiation,
ozone layer formation, and respiratory inorganics) or end-point categories
(human health, ecological health, and resource depletion).
2. Classification of the different emissions according to the impact category
they affect. For example, CO , CH , and N O emissions are classified in the
2
2
4
category of climate change. We need to be aware that some substances can
affect several impact categories.