Ferro-processos aplicados à degradação de efluente da produção de trifluralina

Abstract

In this work, comparative studies about the performance of iron-processes were carried out in the pre-treatment of effluent streams samples (under high concentration) from the trifluralin herbicide production (amination water). It was investigated the use of iron in the Fe²+/H2O2 system (Fenton process); in photoprocess Fe²+/H2O2/UV (photo-Fenton system), preceded of non-Fe²+ addition (photoperoxidation system); Fe° (Fe°-reduction) and electrochemistry process (electrocoagulation system). It was used factorial design to optimize experimental conditions and the effects of variables were evaluated. The investigated variables were concentration of reagents and pH, in the Fenton, photoperoxidation, photoFenton e Fe°-reduction process (amination water, 50% v/v); electrode type and electrodes’s distance from each other, cell voltage and pH, in the electrocoagulation process (amination water, 25% v/v). It was adjusted an analytical procedure for the determination of the chemical oxygen demand, COD, for the samples containing a high saline level, propitiating the correction of the interference from chloride ion in a concentration range of approximately 15% (amination water). In standard samples, the results presented a relative standard deviation (RSD) of 10% and relative error of –3%. When using amination water samples the results presented a RSD of 7%. The applied process were evaluated through UV-vis spectra, COD, H2O2 consumption (Fenton, photoperoxidation, photo-Fenton process) and acute toxicity. All processes were positively affected by the increasing of concentration of reagents and decreasing of pH. The electrocoagulation process achieved better efficiency when shorter electrodes’s distances were used, higher voltages and extreme conditions of pH (alkaline conditions were better), independently of the electrode type tested. The experiments were carried out in semi-bach tank stirred reactor. This way, after 2 hours of treatment under optimized conditions (Fenton: 1000 mL; pH 5; 1500 mg H2O2 L-¹; 500 mg Fe²+ L-¹; photoperoxidation- T: 50°C; 500 mL; lamp power: 125 W; pH 5; 1600 mg H2O2 L-¹; photo-Fenton- 500 mL; lamp power: 125 W; 2500 mg L-¹ de H2O2; 300 mg L-¹ de Fe²+; Fe°-reduction- 1000 mL; 10000 mg Fe°; pH 5; electrocoagulation- 200 mL; voltage cell: 5 V; pH 9; stainless steel electrodes distance: 2 cm) the best results were, in relation to color reduction (λmax = 420 nm), electrocoagulation (96%), Fe°-reduction (96%), photo-Fenton (89%), Fenton (60%) e photoperoxidation (13%). In addition, the COD reduction showed better results when using electrocoagulation (60%), photo-Fenton (20%), Fe°-reduction (15%) e photoperoxidation (6%). Considering acute toxicity reduction, the best results were achieved through the electrocoagulation process. In all processes, the reactions’s kinetic was the limiting factor to achieve better efficiency.