## 4 Removal of Pharmaceuticals during Wastewater Treatment  
### Conventional Treatments  
Conventional wastewater treatment consists of a combination of physical, chemical, and biological processes and operations to remove solids, organic matter, and, sometimes, nutrients from wastewater. General terms are used to describe different degrees of treatment in order of increasing treatment level; preliminary, primary, secondary, and tertiary and/or advanced wastewater treatment. In some countries, disinfection to remove pathogens sometimes follows the last treatment step [44]. It has been shown that pharmaceuticals can be removed only partially, as these wastewater treatment plants are  
Figure 1: Sources of pharmaceutical contamination. not designed for full removal [1]. Depending on the composition of wastewaters, preliminary treatments with activated sludge systems or classic membrane bioreactors may be needed [45]. However, membrane fouling comprises a significant obstacle to their broad application [46]. Pharmaceutical compounds are characterized by their limits of elimination by volatilization because of their low vapor pressure and pKa values between 3 and 10. Some drugs, such as ibuprofen, diclofenac, and carbamazepine, include extremities vulnerable to biodegradation and sorption. According to the review of [PERSON] et al. [47], diclofenac is removed by \(\leq\)50%, and any carbamazepine removal is low. From the study carried out by [PERSON] et al. [48], in Switzerland, they noted the difficulties faced in the removal of different drugs such as ibuprofen, pregnamic acid, and diclofenac with biological and physico-chemical treatments. Additionally, this work reported that there was a difference in the elimination rates within wet and dry seasons. The removal of ibuprofen and ketoprofen was inhibited during winter in comparison to that during the dry period. This can be explained by the difference in the residence time of treated water in treatment plants depending on the rainfall. In fact, the flow rate was three times higher in winter than in the dry period. In addition, [PERSON] et al. [49] found ibuprofen, naproxen, ketoprofen, diclofenac, and bezafibratein seven different sewage water treatment plants in Finland. Despite their effort to remove these pharmaceutical products, they detected them again in the rivers of discharge of sewage water treatment. In fact, in the river of Aurajoki (AUJ), they found low concentrations of all studied pharmaceuticals, but in the river of Seinajoki (SEJ, tributary of Kyronjoki, KYJ), they found a very low concentration, which was explained by the dilution of water up to five times. In the Kokkamenjoki river (KOJ), located in the South Westo f Finland, they found only IBU, NPX, and DIC, which was explained by dilution and also degradation and adsorption processes. The highest removal rate was attributed to ibuprofen with 92% and the lowest one to diclofenac with 26%. In the same context, [PERSON] et al. [50] found analgesic/anti-inflammatory drugs such as ibuprofen and naproxen, as well as the metabolite of acetylsalicyclic acid, salicylic acid, in final effluents at \(\upmu\)g/L levels from 14 sewage treatment plants from the provinces of Manitoba, British Columbia, Quebec, Alberta, Ontario in Canada. The most important parameter for drug degradation is the sludge retention time (sludge age). When the sludge age is 10 to 15 days, partial biodegradation is observed, but after only four days, biodegradation of pharmaceuticals is almost zero [51].The sludge age required for degradation of aspirin, ibuprofen, bezafibrate, and sulfamethoxazole is 2 to 5 days [52], although, for iopromide, roxithromycin, and diclofenac, 5 to 15 days are required for significant degradation [53]. Some products such as carbamazepine and diazepam remain unmodified even after \(>\)20 days [54]. Hydraulic retention times \(>\)27 days and sludge retention times \(>\)35 days have led to high removal of estrogens from water.