Insights into removal of antibiotics by selected microalgae (Chlamydomonas reinhardtii, Chlorella sorokiniana, Dunaliella tertiolecta and Pseudokirchneriella subcapitata)

The increasing contamination of worldwide water with numerous antibiotics has become an emerging environmental concern due to the considerable ecotoxicity and health issues associated with some antibiotics. Microalgae-mediated remediation of pollutants is of growing scientific interest due to the ability of microalgae to take up organic/inorganic nutrients and produce biomass that can be further used for energy or biofuel generation. Elimination of pollutants from water in microalgae experiments includes various mechanisms, such as photodegradation, sorption in biomass and biodegradation. The sorption of pollutants by microalgae has been widely reported, but few studies have proven the biodegradation of pollutants by microalgae. In this work, the ability of four selected microalgae (Chlamydomonas reinhardtii, Chlorella sorokiniana, Dunaliella tertiolecta and Pseudokirchneriella subcapitata) to remove 9 antibiotics and the antidepressant venlafaxine was studied under different experimental conditions. The results show that the highest efficiency for antibiotic removal was obtained with microalgae exhibiting the highest growth rates. Promising results have been obtained from C. reinhardtii and D. tertiolecta cultures, which exhibited a rapid growth and good removal percentages for some of the antibiotics studied. Photodegradation was the main removal mechanism for the 3 fluoroquinolones studied (ciprofloxacin, ofloxacin, norfloxacin) and pipemidic acid (>78%), while for the 3 macrolides (azithromycin, clarithromycin, erythromycin), the efficiency of photodegradation was less than 5%. For the macrolides, the combination of abiotic phenomena, sorption onto the biomass and biodegradation were the mechanisms responsible for total removal. Trimethoprim and venlafaxine were shown to be very stable compounds with low removal percentages. Sulfapyridine appeared to be eliminated mainly by algae biodegradation since low sorption and photodegradation efficiencies were observed. The presence of products resulting from transformations of azithromycin, erythromycin and sulfapyridine in the liquid phase of live algae confirmed that biodegradation is one way by which microalgae eliminate these antibiotics.