Use of solar advanced oxidation processes for wastewater treatment: follow-up of degradation products, acute toxicity and estrogenicity

Micropollutants are emerging as a new challenge to the scientific community. The discharge of treated effluent from wastewater treatment plant (WWTP) is a major pathway for the introduction of emerging contaminants into surface water. Solar advanced oxidation processes can achieve high and consistent micropollutants’ removal. This study deals with the destruction of trace organic contaminants in secondary treated effluents by (i) sulphate radical based (SO4-) homogeneous photo-Fenton using peroxymonosulphate as an oxidant, ferrous ion Fe(II) as catalyst, (ii) hydroxyl radical (○OH) heterogeneous photocatalysis using suspended titanium dioxide (TiO2) as catalyst, (iii) photolysis and solar irradiation as a light source. Solar advanced oxidation processes of wastewater was conducted in a panel solar pilot and the efficiency of this treatment was evaluated on the basis of micropollutants’ disappearance, reduction of total organic matter content (TOC), and measurement of the final estrogenicity. The chemical analyses of the wastewater collected showed that several contaminants persisted at the end of its treatment in the WWTP. Contaminants elimination was followed by Liquid Chromatography/Quadrupole ion trap Mass Spectrometry analysis after a pre-concentration 100:1 by solid phase extraction. 74 target micropollutants were identified. Some of them were found at trace level also after the applied AOPs. The ecotoxicity of the effluent wastewater was evaluated using different commonly adopted bio-tests as Daphnia magna, Vibrio fischeri, Brachionus calyciflorus, Spirodela polyrhiza, Pseudokirchneriella subcapitata. These standard methods can give an idea about of quality of wastewater, but they are not able to respond also to the presence of estrogenic activity, that can be a crucial problem. For overtake this point, the treatment efficiency was provided by estrogenic activity measurements based on the use of bioluminescent HELN ERa cell line. The order of micropollutants elimination efficiency under the experimental condition evaluated was solar heterogeneous photocatalysis with TiO2 > solar PMS/Fe (II) >solar photolysis.