Page 296 - Materials Chemistry, Second Edition

Life Cycle Analysis of Anaerobic Digestion of Wastewater Treatment Plants 277

wastewaters. Also, sulfide inhibits the biological activity of anaerobic bac-
teria and methanogens. Thus, it has been included as a key mechanism to
control the AD process (Barrera et al., 2015). Considering sulfide as a key
element in AD systems is essential to understanding the physicochemical
interactions in the inorganic chemistry of wastewater, which is especially
relevant to predicting the fate of inorganic nutrients such as S, P, and Fe to
optimize nutrient recovery (Flores-Alsina et al., 2016).

Another emerging field of study in AD is the physicochemical framework, not
only for single AD processes, but for plant-wide modeling approaches focused on
the analysis of the fate of key inorganic components (Flores-Alsina et al., 2015).
What happens in a WWTP has deep consequences for water bodies and the sew-
age system. For example, aluminum and iron sulfate have been intensively used
as coagulants in wastewater treatment, and this has caused a tremendous impact
on the economy of water management, as added sulfate is the main source of cor-
rosion in the sewage system due to the SRB activity producing sulfide (Pikaar
et al., 2014). From a circular economy perspective, the physicochemistry of the
wastewater treatment processes affects mainly the inorganic resource recovery
potential, especially for P, Mg, and Fe. A systematic study of precipitation pro-
cesses for multiple minerals in wastewater treatment, including amorphous cal-
cium phosphate, calcium carbonate monohydrate, dicalcium phosphate hydrate,
octacalcium phosphate, and struvite, has been conducted by Kazadi Mbamba et al.
(2015). The mineral precipitation can predict not only the potential P recovery by
struvite formation but also the pH of the system. This approach has been highly
useful to predict the real fate of P, Ca, P, Mg, S, and Fe in AD processes by includ-
ing the Fe-S-P interaction that can be derived from SRB activity, since sulfide can
compete with other anions such as phosphate and carbonate to entrap mono- and
2+
2+
bivalent cations such as Fe , Ca , Mg , and K (Flores-Alsina et al., 2015). This
+
2+
+
chemistry module has been used for accurately predicting actual pH and P, NH ,
4
2+
and Mg fate in the digestate on AD, especially relevant to P recovery potential as
struvite (Flores-Alsina et al., 2016).
13.2 LIFE CYCLE ASSESSMENT (LCA) OF ANAEROBIC DIGESTION
OF URBAN AND INDUSTRIAL WASTEWATER TREATMENT
WWTPs are implemented to decrease the environmental impacts of municipal and
industrial wastewater discharges. Quality requirements in both cases are completely
satisfied with the conventional activated sludge (CAS) technology, traditionally used
for urban wastewater (UWW) (Pintilie et al., 2016). CAS technology shows good
sewage treatment efficiency with low operating cost. One recently emerging tech-
nology for both urban and industrial wastewater treatment is the use of membrane
bioreactors (MBRs), in particular aerobic membrane bioreactors (AeMBRs). This
technology allows the complete degradation of microcontaminants or pollutants
compared with conventional biological systems, showing other advantages over the
CAS process: excellent effluent quality, good disinfection capability, reduced foot-
print and sludge production, and so on (Ioannou-Ttofa et al., 2016).