WWTPs removal rates

As WWTPs removal rates are lacking, modelling is important however, there is a need to improve their accuracy for a better evaluation [43]. 

The fate of hormones in urban WWTP has been abundantly documented. Several studies reported high removal rates for hormones from the liquid phase of sewage, particularly in those WWTP using activated sludge processes. For instance, removal rates of 40-96%, 40-100%, 40-96%, and 40-98% for, respectively, El, E2, E3, and EE2 were reported in WWTP all around the world. Nevertheless, residual hormone concentrations of < 0.3-100 ng L 1 of El, < 0.2-20 ng L 1 of E2, < 1-275 ng L 1 of E3, and < 0.3-7.5 ng L 1 of EE2 have been detected in treated effluents, which shows that hormones were not completely removed by the treatment processes [82, 84, 86, 90, 95-97]. 

The environmental impact of hormones seems to be mainly related to liquid effluents. However, in the light of the high levels of hormones present in solid matrices such as manure or sludge from WWTP with poor hormone removal rates (e.g. enhanced precipitation [116]) there, it is still a need to implement treatment processes to efficiently remove hormones from sludge and manure. 

Removal Rates in WWTP from the Ebro River Basin. 221... 

Fig. 3 Range of removal rates (a) and average removal efficiencies (b) for some of the most ubiquitous pharmaceuticals under conventional activated sludge treatment in the whole set of WWTPs under investigation...

The removal rate of pharmaceuticals by WWTPs depends on factors such as reactor configuration, redox conditions, temperature, hydraulic retention time (HRT) and solid retention time (SRT). SRT is the average retention time of sludge... 

If the drug/metabolites are persistent and at the same time very polar and do not bind to solids, they are not retained neither degraded in the WWTPs. Therefore, they can easily reach the aquatic environment [11]. This is the example of the ubiquitous presence of carbamazepine in natural waters due to its persistence and low removal rate (below 20%) [43]. 

Conventional wastewater treatment plants (WWTPs) were not designed for an efficient APIs removal. The sludge retention time (SRT) is one of the crucial parameters, which influence on the design, operation and control of WWTPs. APIs can be divided into three major groups compounds with optimum SRT range for which their removal is the most effective (e.g., antibiotics and antiinflammatories), compounds on which SRT has no impact (e.g., anticonvulsants, p-blockers and hormones), compounds with visible influence of SRT on their removal rate (e.g., lipid regulators) [43]. 

Opioids showed different behavior during wastewater treatment. As observed in similar studies performed in other European countries (Castiglioni et al., 2006 Bones et al., 2007) METH and its metabolite EDDP were poorly or not removed in the Spanish WWTPs investigated (Boleda et al., 2007,2009). Maximum removal rates observed for METH and EDDP reached 53% and 15% respectively (Fig. 6.2). 

In recent years, several pnblieations have reported the occurrence of illicit dmgs and metabolites in waste and surface waters in Spaia The studies performed so far have shown, in general, incomplete removal of these compounds in the WWTPs investigated, and their consequent presence in the receiving river waters, although at lower concentrations than in wastewater. CO and BE seem to be the most efficiently removed compounds, and cannabinoids and amphetamine-like compounds the least. Nevertheless, removal rates varied widely between compounds and plants and the interpretation of the results must be handled with caution, since sample collection in most of the cases did not take into account the WWTP l draulic residence time and water samples occasionally were not composite. 

Total removal rates in Milan, Lugano, and Cbmo WWTPs were, respectively, 97%, 68%, and 89%, indicating a good, but incomplete, removal of ilhcit drags in these plants. In the Como plant, the removal was only 29%, if we also take into accormt morphine and codeine. However, this low removal rate is a particular case, because of the very high concentrations occurring in WWTP influents. 

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