Page 191 - Materials Chemistry, Second Edition

172 Life Cycle Assessment of Wastewater Treatment

9.1 INTRODUCTION
In the last few years, special attention has been paid to the presence of pharmaceuti-
cal compounds in the environment because of their bioactivity, widespread use, and
potential health and ecological risks. The main routes for the appearance of pharma-
ceuticals in the environment are the release of wastewater effluents from wastewater
treatment plants (WWTPs) and also land application of sewage sludge generated
as a by-product of wastewater treatment. The European Union (EU) included for
the first time in 2015 the monitoring of seven pharmaceutical compounds in sur-
face water (EU, 2015). These compounds were included in the first watch list of
substances for Union-wide monitoring in the aquatic environment, which was
composed of 10 substances/groups of substances. The pharmaceutical compounds
included in the watch list are the anti-inflammatory drug diclofenac, three macrolide
antibiotics (erythromycin, clarithromycin, and azithromycin), and three hormones
(17-α-ethinylestradiol, 17-β-estradiol, and estrone). In Europe, the implementation
of a directive concerning urban wastewater treatment (EC, 1991) has increased the
number of WWTPs, because it stated that by the end of 2005, secondary treatment
had to be applied to wastewater coming from settlements of more than 10,000 popu-
lation equivalent and to wastewater coming from settlements of more than 2,000
population equivalent when it is discharged to fresh waters and estuaries. As a result,
the European Commission has reported that the amount of sewage sludge gener-
ated in the EU, due to the implementation of the wastewater treatment directive, has
increased from 5.5 million tons dry matter (d.m.) in 1992 to 9 million tons by the end
of its implementation. Sewage sludge generated in urban WWTPs is of great inter-
est as a fertilizer because of its nitrogen, phosphorus, and organic matter content.
Therefore, the application of sewage sludge generated in WWTPs to soils enables not
only the disposal of this increasing by-product of wastewater treatment but also tak-
ing advantage of its agronomic properties as a fertilizer. That application is promoted
in the EU by the sewage sludge directive 86/278/EEC (EC, 1986), which encourages
the use of sewage sludge in agricultural soils and regulates its application to prevent
harmful effects on soil, vegetation, animals, and man. Nevertheless, in that directive,
concentration limits are fixed only for seven heavy metals (cadmium, copper, nickel,
lead, zinc, mercury, and chromium) for sludge that is intended for application to agri-
cultural soils. WWTPs are not designed to eliminate pharmaceutical compounds,
but when removal occurs, it can be due to biodegradation or to sorption onto sludge,
mainly in the case of compounds with high solid-water distribution coefficient (K )
d
(Martínez-Alcalá et al., 2017). For some pharmaceuticals, biodegradation can result
in the release of the parent compounds from their metabolites and conjugated forms,
resulting in an increase, instead of a decrease, of the concentration of the pharma-
ceutical compound after wastewater treatment. Wastewater treatment can even affect
enantiomeric compounds, causing their concentrations to deviate from the racemic
proportions. For instance, Evans et al. (2015) determined the enantiomeric concen-
trations of nine pharmaceutical compounds in wastewater and in digested sludge,
which had undergone activated sludge and anaerobic digestion. They reported that
the nine compounds monitored had significantly different enantiomeric profiling in
wastewater and in sludge. Moreover, the enantiomeric fractions of some compounds