Comparação da eletroxidação de compostos orgânicos usando eletrodos plano e tela considerando a área eletroativa e a transferência de massa
Verzola, Marco Aurélio
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Toxic organic compounds present in industrial effluents have their concentration limits for disposal determined by increasingly strict environmental and sanitary laws, as they can cause serious problems to the environment and human health. Often, the treatment of these effluents is carried out using biological processes, however, some classes of compounds, including phenolic, are quite refractory to this type of treatment, thus requiring the use of other technologies. Due to these factors, electrochemical techniques have stood out as a promising treatment alternative, mainly for their efficiency and environmental compatibility. However, the energy consumption of the process still represents a factor to be improved for its effective application. In this work, we studied the electrochemical degradation of phenol using different geometries (plate and mesh) of boron-doped diamond (BDD) electrodes. In a first step, the electroactive area of these electrodes was determined (76.6 cm² - mesh and 60.5 cm² - plate) for an effective comparison of phenol degradation applying the limiting current calculated considering the electrochemical and the geometric area. The process was optimized regarding the mass transfer, with the best mass transfer coefficient values obtained using a flow velocity of 0.30 m s-1 (flow velocity). Considering the phenol degradation, the plate BDD coupled with turbulence promoters presented better results both in terms of mineralization rate and mass transfer (km= 1,26 x 10-4 m s-1), compared to the mesh BDD (km = 1,06 x 10-4 m s-1). Subsequently, it was found that the use of AE instead of AG for the calculation and application of the limit current in the degradation process led to an increase of 18.9% in the removal rate of COD. The same trend was observed for the global current efficiency (increase from 53% to 62%), leading to a reduction of the average energy consumption from 45 to 33 kWh kg-1 (considering 75% removal of the initial COD). In a third step, the electrochemical degradation was evaluated in absence of the turbulence promoter. In this case, the mass transfer coefficient decreased from 1.26 x 10-4 m s-1 to 0,48 x 10-4 m s-1, reducing the mineralization rate. The global current efficiency decreased from 62% (with TP) to 23% (without TP) leading to an increase in specific energy consumption from 33 to 90 kWh kg-1. Taking into account the results of the previous steps, the plate BDD + TP electrode was used in modulated current conditions aiming at a more effective reduction of the specific energy consumption, which effectively occurred, as there was an 85% reduction in consumption energetic, corresponding to 24.4 kWh kgCOD-1. The significant reduction is attributed to the high mass transfer rate resulting from the use of TP, associated with the specific design of the reactor used, which led to a 67% increase in current efficiency. Additionally, the consideration of AE for the calculation and application of the limit current during the modulation also allowed the process to operate with current values closer to the real limit current. Finally, the application of modulated current in the electrochemical degradation of a real laboratorial wastewater was evaluated. The results validated the effectiveness of the process by combining TP and modulated current to reduce energy consumption, thus proving to be an alternative for the treatment of effluents containing polluting organic compounds.
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