Solar photo-Fenton at circumneutral pH using Fe(III)-EDDS compared to ozonation for tertiary treatment of urban wastewater: contaminants of emerging concern removal and toxicity assessment

Abstract Solar photo-Fenton (SPF) at circumneutral pH with ethylenediamine-N,N'-disuccinic acid (EDDS) in raceway pond reactor was compared to a well-stablished process (ozonation) in the degradation five contaminant of emerging concern (CECs, namely Caffeine, Carbamazepine, Diclofenac, Sulfamethoxazole and Trimethoprim) at the initial concentration of 100 μg/L each in urban wastewater treatment plant secondary effluent (UWWE) at pilot scale with natural sunlight. Both were found to be effective in the removal of the target CECs. Ozonation treatment was faster being able to degrade 80% of each CEC in UWWE within the early 15 min (18.0 mgO3/L consumed). Acute (using activated sludge, Vibrio fischeri and Daphnia magna) and chronic (using activated sludge at 72 h of sample contact and V. fischeri at 244 h of sample contact) toxicity were also evaluated. Acute toxicity evaluated by activated sludge did not show any toxic effect. V. fischeri gave less sensitive results compared to D. magna tests. Lower toxicity levels for SPF were observed. Highest acute toxicity was observed for D. magna in UWWE treated by ozonation. Relevant chronic toxicity assessed by activated sludge and V. fischeri was observed in almost all analysed samples, despite 80% of the CECs were eliminated. Successful performance of AOPs for CEC removal is not a guarantee of obtaining safe alternative water sources.