Page 57 - Materials Chemistry, Second Edition

38 Life Cycle Assessment of Wastewater Treatment

impacts are calculated and relate the impacts of the other scenarios to the one con-
sidered as reference.

3.3 EVALUATION OF CONVENTIONAL WWTPS:
METHODOLOGICAL ASSUMPTIONS AND
ENVIRONMENTAL INDICATORS

The evaluation of conventional WWTPs by LCA started in the 1990s (Emmerson
et al., 1995; Roeleveld et al., 1997), and two approaches were followed: the identifi-
cation of improvement alternatives for a single plant (Hospido et al., 2004) and the
comparison of different technologies toward an equivalent target (Coats et al., 2011;
Gallego et al., 2008; Meneses et al., 2010; and Rodriguez-Garcia et al., 2011).
The major differences found among the different LCA reports on wastewater
treatment systems are the selection of the FU, the system boundaries, and the envi-
ronmental indicators. The most common FUs used in LCA studies of WWTPs are
the flow rate of treated water (the simplest approach) and the quantification of the
environmental load associated with a one-person equivalent (Table 3.1). The former
has the advantage of being based on physical data, while the latter tends to be used
for comparative purposes, since the design project of wastewater facilities includes
this parameter as a design value that integrates the composition and flow of the influ-
ent. However, neither alternative reflects the function of the system and operational
efficiency in terms of eutrophication reduction. One interesting alternative is the Net
Environmental Benefit (NEB) approach developed by Godin et al. (2012), who calcu-
lated the difference between avoided potential impacts, such as those associated with
influent discharge and those associated with WWTP operation.
The quality of LCI data is another issue of special interest, considering that inven-
tory data may be subject to substantial variability in terms of flow and composition
of the influent (Yoshida et al., 2014a). When it comes to analyzing data representa-
tiveness, it is evident that the operation of a WWTP is not a satisfactory example of

TABLE 3.1
Functional Units Used in Some LCA Studies of Wastewater Treatment Plants
Functional Unit
Value References
Cubic meters of Brix (1999), Hospido et al. (2004), Ortiz et al. (2007), Høibye et al. (2008),
treated water Renou et al. (2008), Pasqualino (2011), Venkatesh and Brattebø (2011),
Hospido et al. (2012), and Li et al. (2013)
Cubic meters and Rodríguez-García et al. (2011)
kilograms of
PO 4 removed
3−
Population equivalent Emmerson et al. (1995), Tillman et al. (1998), Mels et al. (1999),
Lundin et al. (2000), Kärrman and Jönsson (2001), Dixon et al. (2003),
Machado et al. (2007), Gallego et al. (2008), and Hospido et al. (2008)