Formation of micropollutant decomposition by-products during oxidation processes supported by natural sunlight

The paper presents the comparison of micropollutant removal degrees after the O₃ and O₃ / H₂ O₂ processes supported by sunlight radiation. These tests were conducted on selected organic micropollutant water solutions prepared on the base of deionized water. The examined compounds belong to the group of pharmaceuticals (benzocaine, caffeine, carbamazepine (CBZ), diclofenac sodium salt, ibuprofen sodium salt (IBU)), hormones (β-estradiol, 17α-ethinylestradiol, mestranol, progesterone), pesticides (triallate, triclosan, oxadiazon), food additives (butylated hydroxytoluene (BHT)) and dyes (acridine). Processes were carried out at various O₃ doses: 1, 2, 3, 5 and 10 mg/L. The reaction vessels containing the test solutions were exposed to solar radiation for 10, 20, 30 and 60 min. The process effectiveness and the identification of the formed compound decomposition by-products were assessed by the use of gas chromatography coupled with mass detection based on the NIST v17 mass spectra database. It was noted that the presence of another type of oxidant in the form of H₂ O₂ during the O₃ /sun light process results in the reduction of the half-life of CBZ, IBU, BHT, and all tested hormones and pesticides. On the other hand, the presence of H₂ O₂ affected the type and the number of generated micropollutant intermediates. The highest compound removal degrees, which exceeded 92%, were noted during the implementation of sunlight supported process for micropollutants belonging to the group of hormones and pesticides. Also, it was observed that the irradiation of samples with sunlight resulted in a decrease in the number of formed decomposition by-products. The conducted toxicological analysis confirmed the reduction of the toxic nature of samples subjected to sunlight assisted by the O₃ /H₂ O₂ process compared to samples treated by the action of O₃ /H₂ O₂ performed in a dark chamber.