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

• Antiepileptic drug carbamazepine (CBZ) wastewater mineralized by US–UV–H2O2 process.
• An empirical model that includes the scavenger effect was applied satisfactorily.
• Carbamazepine photodegradation occurs mainly through a two steps radical mechanism.
• Under optimum conditions, mineralization reached 93% in 35 min.
• Improvement in mineralization rate with US radiation is not due to a better mixing.

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 10–15 min, 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 = 0.0014 min−1 mM−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 = 0.0004 min−1 mM−1).Experiments performed under the US–UV–H2O2–Fe system proved the important contribution of OH radicals. The maximum mineralization (93% in 35 min) was reached for [Fe] = 15 ppm and [H2O2] = 680 ppm.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.