Degradation of Codeine Phosphate by simultaneous usage of eaq− and •OH radicals in photo-redox processes: Influencing factors, energy consumption, kinetics, intermediate products and degradation pathways

Abstract Iodide ions and the ZnO catalyst under UV irradiation, i.e. ZIU, were used to produce both reductive and oxidative agents at the same time for Codeine Phosphate (CP) destruction. The results revealed that ZnO adsorption (in dark condition), UV irradiation, UV/Iodide, and UV/ZnO treatments respectively display 0.46%, 46.21%, 54.97%, and 66.71% CP destruction, the ZIU procedure exhibits 89.46% destruction efficiency. Additionally, detecting the destruction compounds through liquid chromatography-mass spectroscopy specified that the all CP molecules and generated metabolites change to simple ring-shaped metabolites in 5 min and linear compounds such as formaldehyde, acetaldehyde, butyric acid, formic acid, acryl aldehyde, acetic acid within 15 min reaction time, respectively. Maximum destruction efficiency happened at natural pH (7). Also, fourteen intermediates were recognized during this process, which remain in reactor for just 5, 10, and 15 min. In conclusion, the pseudo first-order kinetics model was employed to explain the destruction process. Base on this model, the observed rate constant (kobs) and the related rate (robs) respectively, decrease and increase from 0.543 to 0.189 min−1 and from 54.30 to 79.20 mg L−1 min−1 with the addition of CP concentration from 100 to 400 mg L−1. In effect of co-existing water anions on CP destruction investigation the internal effect filter of bicarbonate, chloride, nitrate and sulfate were calculated to be 5.7%, 5.1%, 3.7% and 2.5.9%, and reaction between anion and reactive agents 7.9%, 8.05%, 3.53%, 2.32%, respectively. In details, existence of nitrate, bicarbonate, sulfate and chloride anions decrease CP destruction efficiency approximately 13.76%, 13.15%, 7.23% and 4.82%, respectively. COD and TOC at studied CP solution in ZIU system, decreases approximately 43.91% and 53.33% within 30 min reaction time, 60.34 and 64.17 at 60 min process time, respectively, which can’t be effective-cost for larg-scale applications. Also, for more mineralization of CP metabolites, the ZIU reactor should be coupled with a bioreactor to employ biodegradation.