Page 297 - Materials Chemistry, Second Edition

278 Life Cycle Assessment of Wastewater Treatment

However, energy requirements (including electricity consumption) should be
taken into account regarding the sustainable concept of energy-sufficient WWTPs.
Thus, some studies determine that aerobic processes (such as CAS or AeMBR)
represent a large percentage of the total WWTP energy consumption (Gu et al.,
2017; Pretel et al., 2016). Moreover, aerobic WWTP does not exploit the potential
energy contained in the organic matter and the fertilizer value of nutrients (Pretel
et al., 2016).
In this sense, anaerobic reactors have emerged as an alternative for the sustain-
ability treatment of industrial as well as urban wastewaters, especially since they can
be operated under high SRT and very low HRT, providing them with great poten-
tial for application (Martinez-Sosa et al., 2011). In this context, although anaerobic
reactors for wastewater treatment have been known and used for over 100 years, a
critical technological advance that expanded AD was the development of methods
to concentrate methanogenic biomass in the reactor, especially with very low solids
concentration in the wastewater (1%–2%). Other advantages are that only a small
portion of the organic material is converted into microbial biomass as compared
with aerobic systems, the excess sludge usually being more concentrated, with better
dewatering characteristics. This is due to the transformation of the organic matter
into biogas, which is used afterward for the production of electricity and energy
(Weiland, 2010).
Anaerobic technologies for wastewater treatments combine different attractive
features (high efficiency in chemical oxygen demand [COD] removal, low values of
HRT, biogas production) with a major disadvantage; that is, the energy requirements.
However, this problem could be solved with the self-produced biogas. Additionally,
CH , N O, and CO emissions (as escaped gases or dissolved in the permeate) can
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be derived from the WWTP operation, depending on the reaction system and the
characteristics of the influent (Meneses-Jácome et al., 2016). For that reason, envi-
ronmental evaluation of these processes must be carried out.
LCA methodology is applied to determine the environmental feasibility of pro-
cesses and products from the “cradle to grave perspective.” LCA performs the
evaluation of all types of potential impacts to the environment, from depletion of
natural resources and energy requirements to emissions to air, land, or water (eutro-
phication, acidification, etc.) as well as resources recovery from the process. All
of these are assessed within a consistent framework according to the International
Organization for Standardization (ISO) standards (Hospido et al., 2012; Smith et al.,
2014; Massara et al., 2016). LCA analysis can also be used as a tool for the evalua-
tion of different scenarios for improving processes under study, identifying process
bottlenecks and possible opportunities toward which specific research efforts should
be focused. However, although LCA in the field of wastewater treatment has been
applied for the last 21 years (Corominas et al., 2013), its application to anaerobic
wastewater treatment has several constraints. On the one hand, comparison between
studies is difficult, since functional units or references for calculation differ between
works focused on biogas production (energy units) and those devoted to water treat-
ment (volume or treat capacity units). On the other hand, interpretation of results
is difficult and is not always harmonized due to the lack of unified criteria in the