The industrial revolution and rapid urbanization have led to increased activity in various industrial sectors. Most of these industries consume large amounts of freshwater, producing wastewater containing numerous pollutants. These substances, which are increasingly diverse and harmful to organisms , require contaminated wastewater to be treated more efficiently.

Microalgae, already used in wastewater treatment, appear to be a potential solution to this problem thanks to their ability to absorb and adsorb pollutants.

In this study, we monitored the ability of two microalgae species, Scenedesmus obliquus and Chlorella vulgaris, to purify artificially contaminated water over 96 hours: (i) with a dye, Rhodamine B (RhB), between 0.5 and 5 mg.L -1 , (ii) with a pharmaceutical molecule, paracetamol (APAP), between 1.5 mg.L -1 and 15 mg.L -1 . In addition to pollutant removal monitored by spectrophotometry, toxicity to microalgae was determined by examining growth, maximum quantum efficiency of photosystem II (Fv/Fm) and non-photochemical quenching of photosystem II (Y(NPQ)).

Using S. obliquus as an example, we observed a dose-response relationship for RhB through degradation rate and time. The maximum degradation rate of 53 % in 24 h was achieved for the lower dye concentration, while only 17 % was achieved in 96 h for the highest. For the same periods, a lower degradation rate was reported in the conditions without microalgae: only 9.9 % for the lowest dye concentration and 4.7 % for the highest. This indicates that the decrease in RhB was not due to abiotic factors.

Concerning APAP for both species, we did not find any effect of microalgae on this pharmaceutical removal. Conversely, the controls showed a higher degradation rate than the conditions with microalgae, suggesting an inhibition of photolysis by the algal cells.

The lack of effect on the physiological state of S. obliquus showed that it is resistant to APAP degradation and contributes to RhB degradation at these concentrations. In contrast, C. vulgaris was physiologically affected by the highest pollutant concentrations, showing a decrease in Fv/Fm values and a significant increase in Y(NPQ) associated with lower growth.

Based on the results obtained, Scenedesmus obliquus seems to be a potential candidate for phytoremediation.