Degradation of Agro-Industrial Wastewater Model Compound by UV-A-Fenton Process: Batch vs. Continuous Mode.

The degradation of a model agro-industrial wastewater phenolic compound (caffeic acid, CA) by a UV-A-Fenton system was investigated in this work. Experiments were carried out in order to compare batch and continuous mode. Initially, batch experiments showed that UV-A-Fenton at pH 3.0 (pH of CA solution) achieved a higher generation of HO•, leading to high CA degradation (>99.5%). The influence of different operational conditions, such as H 2 O 2 and Fe 2+ concentrations, were evaluated. The results fit a pseudo first-order (PFO) kinetic model, and a high kinetic rate of CA removal was observed, with a [CA] = 5.5 × 10 -4 mol/L, [H 2 O 2 ] = 2.2 × 10 -3 mol/L and [Fe 2+ ] = 1.1 × 10 -4 mol/L ( k CA = 0.694 min -1 ), with an electric energy per order (EEO) of 7.23 kWh m -3 order -1 . Under the same operational conditions, experiments in continuous mode were performed under different flow rates. The results showed that CA achieved a steady state with higher space-times (θ = 0.04) in comparison to dissolved organic carbon (DOC) removal (θ = 0-0.020). The results showed that by increasing the flow rate ( F ) from 1 to 4 mL min -1 , the CA and DOC removal rate increased significantly ( k CA = 0.468 min -1 ; k DOC = 0.00896 min -1 ). It is concluded that continuous modes are advantageous systems that can be adapted to wastewater treatment plants for the treatment of real agro-industrial wastewaters.