Degradation of azole pesticides in WWTP effluent by hybrid advanced oxidation processes: UV, O3, US, EO, US/UV, O3/EO, O3/US, UV/O3, UV/EO, UV/O3/US, and UV/O3/EO

This work applied different hybrid advanced oxidation processes to remove some priority pollutants in WWTP-effluent. EU Decision 2022/1307 updated the list of priority substances, including some azole fungicides: prochloraz, tebuconazole, tetraconazole, and penconazole. Applied techniques include UV radiation, electrochemical oxidation, ozonation, and ultrasonic cavitation. Authors used these processes individually or integrated in time and space to obtain possible synergies. The innovation and novelty of this work lie in its breadth and depth. Up to eleven hybrid advanced oxidation processes were studied and compared from different perspectives: 1) kinetics, synergy, and estimation of the different reaction pathways; 2) mineralization power and oxidation state of the residual carbon in solution; 3) electrical energy consumed per order of magnitude (costs). The UV process presented the lowest global kinetic rate constant (k M =4.02 ×10 −2 min −1 ) and the highest electrical energy per order (35.7 kWh m −3 ). On the contrary, the highest rate was from the hybrid system EO/UV/O3 at k M = 42.2 × 10 −2 min −1 , showing a very reasonable energy consumption of 5.32 kWh m −3 . From a kinetic point of view, ternary EO/UV/O3 and binary EO/UV systems synergize significantly (f M =+2.00–3.02). Concerning mineralization power, the ternary EO/UV/O3 and binary UV/O3 systems lead the list with 50 % and 35 % TOC removal, respectively, maintaining reasonable energy costs (5–6 kWh m −3 ). Both systems obtain similar values of the oxidation state of the remaining carbon in the solution (close to +4). These remarkable results led the authors to patent the triple unit for the UV/O3/EO process under reference ES 2 941 282 B2, Spanish National Patent. • Hybrid AOPs (O3 +UV+US+EO) were tested to remove EU-priority pollutants in WWTP effluents. • Important synergistic effects were detected on azole pesticide oxidation kinetics (synergy factors >1). • Binary hybrid process UV/O3 reached a TOC and COD removal of 35 % and 93 %, respectively. • Triple hybrid system EO/UV/O3 reached a TOC and COD removal of 50 % and 95 %, respectively.