# Pharmaceuticals Removal from Wastewater with Microalgae: A Pilot Study
## 3 Results and Discussion  
### Occurrence and Removal of Pharmaceuticals  
Of the 63 pharmaceuticals tested, 19 were detected. All the samples presented at least 7 and up to 19 pharmaceuticals, with an average of 14 at the entrance and 10 at the exit of the microalgae system. As expected, average concentrations at the entrance (218.4 ng/L) were significantly (\(p\) < 0.0001) higher than the values at the exit (39.83 ng/L) (Figure 1 and Table S2, Supplementary Materials). Moreover, the maximum values were also much different at the entrance and exit, with values of up to 2950 and 1369 ng/L (venlafaxine), respectively. As for the therapeutic groups at the entrance, the antipsychotics presented a higher average of 381.0 ng/L and maximum concentration. They were followed by antihypertensive (average of 225.8 ng/L), others (average of 215.5 ng/L), and antibiotics (average of 47.9 ng/L) (Figure 1a). At the exit of the WWTP, the order shifted, and the therapeutic group with higher concentrations comprised antihypertensives (average of 60.7 ng/L), followed by antipsychoticsochtics (average of 54.4 ng/L), others (average of 46.8 ng/L), and antibiotics (average of 5.5 ng/L) (Figure 1b). Although this was the therapeutic group's pattern, within each group there are major variations since there are several factors that impact the concentrations of each pharmaceutical. These disparities are due to different therapeutic dosages, consumptions, metabolization, degradation, and removal rates. For example, in the antipsychotics therapeutic group at the entrance, venlafaxine, gabapentin, carbamazepine, and citalopram stand out from the others, with higher average concentrations (867.7, 525.6, 466.8, and 394.2 ng/L). At the exit, venlafaxine, gabapentin, and carbamazepine still stand out from the others, with averages above 68 ng/L (Table S2, Supplementary Materials). As for antihypertensives at the en  
Figure 1: Therapeutic groups’ concentrations (mean and standard deviation) at the entry (**a**) and exit (**b**) of the microalgae system. trance, irbesartan and losartan presented higher values (averages of 430.8 and 368.5 ng/L) than the rest, which presented averages below 176 ng/L. On the other hand, at the exit, losartan and atenolol presented higher average concentrations (145.5 and 75.5 ng/L). In the antibiotics therapeutic group, trimethoprim and sulfaryridine presented the highest averages at the entrance (109.9 and 90.4 ng/L), compared with the other pharmaceuticals with values under 28 ng/L. However, at the exit, all of them presented averages below 12 ng/L. These values were lower than those of similar studies, namely due to COVID, which imposed traveling restrictions, thereby reducing the population in Algarve [9]. Moreover, since this is a WWTP receiving wastewater (WW) from a resort, the data obtained is more prone to this effect than other WWTPs. Regarding experiences 1 (Exp1) and 2 (Exp2), one performed in summer and the other in autumn, there were also higher average values at the entrance of the WWTP for Exp1 and Exp2 (304.0 and 116.5 ng/L, respectively) than at the exit of the WWTP in both experiences (39.75 and 39.92 ng/L, respectively) (Figure 2). There were also significant differences (\(p<\) 0.0001) between the entrance and the final effluent; however, no differences were found between entrances 1 and 2 and between exits 1 and 2. As for the discrepancy at the entrance between both experiences, they are related to the sampling dates, since Exp1 was performed in July and August and Exp2 in September and October. Since August is the month with most people in Algarve, entry 1 values were impacted by this fact [14]. Since the data on pharmaceutical concentrations could bias the interpretation, removal was also calculated to compare the different experiments and therapeutic groups (Figures 3 and 4). The two experiments presented similar average removal values of 79.1% (Exp1) and 71.1% (Exp2), with no significant differences (Figure 3).