# Pharmaceuticals Removal from Wastewater with Microalgae: A Pilot Study
## 4 Conclusions  
In this study, we observed the presence of pharmaceuticals (between 7 and 19) in all the samples with an average of 218.4 ng/L. This confirms that WWTPs are not able to completely remove these compounds and are a hotspot of pharmaceutical contamination in the aquatic environment. At the entrance of the microalgae system, the therapeutic groups, by decreasing average concentrations, were antipsychotics (381.0 ng/L), antihypertensives (225.8 ng/L), others (215.5 ng/L), and antibiotics (47.9 ng/L). However, at the exit, the order changed to antihypertensives (60.7 ng/L), antipsychotics (54.4 ng/L), others (46.8 ng/L), and antibiotics (5.5 ng/L). Moreover, there were significant variations within each group. There were no significant differences between Exp1 and Exp2, except for the initial load, which was related to a higher number of people in the area served by the WWTP at this time of the year. Removal rates ranged from 64.0% (others) to 75.3% (antihypertensive) for the therapeutic groups. Nonetheless, between the different pharmaceuticals, the removal was between 44.7% (ofloxacin) and 100% (sertraline, azithromycin, and sulfamethoxazole). These results  
Figure 6: Correlation between pharmaceutical removal and other parameters. highlight that pharmaceuticals, even those belonging to the same therapeutic group, are removed at very different rates. These promising results were obtained with an HRT of 24 h, lower than that of other similar studies. This allows it to treat the same amount of water with at least half the space and equipment as the published works. As for the correlation between pharmaceutical removal and other factors, we could observe a negative correlation between the sum of all pharmaceuticals' concentrations and the average pharmaceutical removal or the removal of anti-hypertensives. This implies that the removal process by microalgae might be impaired at high concentrations. Positive correlations were observed between nitrates and biomass concentration, anti-hypertensive drugs removal and ammonium concentration, and TN and total pharmaceuticals removal, highlighting that particularly TN and NH4 concentrations can promote better removal of pharmaceuticals. This work supports that the use of a microalgae system can remove pharmaceuticals from an effluent of a WWTP, which can have implications in the design and upgrade of WWTPs, increasing the water quality and, therefore, water reuse. Additionally, since it is a methodology with low installation and operation costs it can also be used in low- and middle-income countries and small communities. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app1316414/s1](https://www.mdpi.com/article/10.3390/app1316414/s1)]([https://www.mdpi.com/article/10.3390/app1316414/s1](https://www.mdpi.com/article/10.3390/app1316414/s1)). Table SI: pharmaceutical compounds included in the scope of the method, and mass detection parameters and limits of detection (LOD) for each compound in water; Table S2: pharmaceuticals' occurrence and removal in experiences 1 (a) and 2 (b) in the microalgae system; Table S3: chemical oxygen demand (COD) and nutrients concentration (mg/L) in the inflow water of the microalgae pathobioreactors. Conceptualization, L.B. and A.P. ([PERSON]); methodology, E.G.d.M. and A.F. ; validation, A.F. ; investigation, A.P. ([PERSON]), E.G.d.M., L.S. and A.F. ; writing--original draft preparation, [PERSON] ([PERSON]), M.R.T., L.B. and A.F. ; writing--review and editing, A.P. ([PERSON]), E.G.d.M., L.S., M.R.T., L.B. and J.V. ; supervision, A.P. ([PERSON]) and L.B. ; funding acquisition, L.B. All authors have read and agreed to the published version of the manuscript. This work received financial support from the Fundacao para a Ciencia e Tecnologia (FCT) through the projects UIDP/50006/2020, UIDB/04326/2020, UIDP/04326/2020, and LA/P/0101/2020 and the project GreenTreat (PTDC/BTA-BTA/31567/2017).