Page 307 - Materials Chemistry, Second Edition

288 Life Cycle Assessment of Wastewater Treatment

for work reported in the main reviews (Yoshida et al., 2013). Usually, these invento-
ries are completed with estimates for those data that are difficult to obtain. Data on
infrastructure and materials are not always considered within LCI data. Inventories
of ADWWS are usually very detailed, and only in very specific studies, such as the
report by Hospido et al. (2010), does the lack of reliable data appear as an aspect to
be solved.
Although methodologies to assess environmental impacts are under permanent
discussion within the LCA community, in the case of LCAs on ADWWS, the most
commonly applied is CML methodology in its different versions. Currently, the
application of ReCiPe methodology is emerging, as it harmonizes mid- and end-
point approaches, and is thus more flexible and uniform than other methodologies
(Goedkoop et al., 2009). As mentioned, the variety of functions present in ADWWS
systems implies the evaluation of a large number of impact categories. Thus, climate
change, acidification potential, eutrophication potential, photochemical oxidation
potential, ozone depletion potential, human toxicity, ecotoxicity, and depletion of
abiotic resources are commonly evaluated in LCAs on ADWWS.
Table 13.2 summarizes the main LCA methodology aspects of works focused on
ADWWS. Herein, only contributions specifically studying LCAs on ADWWS have
been considered.
As explained earlier, the usual scheme for studying the feasibility of ADWWS
using an LCA approach includes biogas production and use as well as land applica-
tion of the organic digestate. Although most LCAs present this process scheme, LCA
results are not comparable between the different works reported in the literature,
mainly due to the different assumptions taken into account.
The first applications of LCA concerning energy production from ADWWS
date from the 2000s; they were not specific to this treatment but were included in
comparative studies of wastewater sludge management at the WWTP (Bridle and
Skrypski-Mantele 2000; Heimersson et al., 2017; Suh and Rousseaux 2002). These
studies were not full LCAs, but they were the first to use the life cycle approach to
sludge management. These works were basically focused on studying the substitu-
tion of the energy required in ADWWS by the energy recovered from the biogas,
mainly in terms of electricity and heating. Moreover, these works pointed to the need
to recover energy and/or materials from wastewater sludge to provide sustainable
sludge management options.
Further LCA studies on ADWWS incorporated more detailed inventory data,
thus obtaining more realistic results. The main objective of these works was the
comparison between different wastewater sludge treatments by quantifying envi-
ronmental impacts. In these works, most of the environmental categories mentioned
in this chapter were included and quantified. Thus, Yoshida et al. (2013) reviewed
LCAs on ADWWS and further use of the organic digestate and compared the
obtained results with other sludge treatment schemes (mainly thermal processes).
The obtained results showed that AD and further land applications, including energy
recovery from biogas and application of organic sludge, reduced GHG emissions
relative to other wastewater sludge treatment schemes.
Another issue of interest regarding LCAs on ADWWS is the study of pre-treat-
ment of wastewater sludge before anaerobic digestion. Carballa et al. (2011) pointed