Modeling the sonophoto-degradation/mineralization of carbamazepine in aqueous solution

The photo-degradation process of the antiepileptic drug carbamazepine (CBZ) is studied under different conditions. Reactions were carried out under UV-H₂O₂, US-UV-H₂O₂ and US-UV-H₂O₂-Fe systems. An important synergistic effect between sonolysis and UV irradiation of 27.7% was quantified using the first order rate constants for carbamazepine degradation. An empirical model that includes the scavenger effect was applied and found to reproduce both degradation and mineralization of CBZ satisfactorily.Comparison experiments of scavenger-loaded conditions demonstrated that the carbamazepine photodegradation occurs mainly through a radical mechanism in two steps: during the first 10-15min, CBZ is completely degraded, whereas TOC barely changes, confirming that intermediates are not easy to mineralize. During this phase, dissolved oxygen (DO) remains in low values and the pair O₂^-/HO₂ is an active contributor to CBZ degradation. Mineralization is low and the scavenger effect from OH radicals is relatively high (kscv=0.0014min^-1mM^-1). From that moment, intermediates are formed and OH radicals are responsible for increased mineralization rate with a gradual decrease in the scavenger effect (kscv=0.0004min^-1mM^-1).Experiments performed under the US-UV-H₂O₂-Fe system proved the important contribution of OH radicals. The maximum mineralization (93% in 35min) was reached for [Fe]=15ppm and [H2O2]=680ppm. A study of the flow pattern inside the reactor showed that improvement in mineralization rate with US radiation cannot be attributed to a positive effect in mixing.