Electrooxidation Of Phenol: An Alternative Wastewater Treatment Of Steel Industry

Abstract:

In the recent decades, the search for efficient and low cost effluent treatment technologies is growing for the organic compounds degradation and metal recovery, to reduce the environmental impacts caused by the release into the environment. Phenols are organic compounds found in effluents of various industrial activities, such as petroleum, pharmaceuticals, plastics, metals, steel and mining. In the steel industry, most of phenol comes from coke making for the production of pig iron, where a large amount of quenching water contaminated with phenol and other organic compounds is generated. Despite the precipitation of sodium phenolate, phenol concentration can be five times higher than the limit established by legislation for disposal. The electrochemical technology through the use of different anodic materials has been shown an effective and viable economically and environmentally in the treatment of various types of effluents. The objective of this work was to evaluate the performance of a plug flow reactor with recycle continuous batch for phenol oxidation, aiming future applications in the effluents treatment from the steel industry. The anode was a RuO2 layered titanium plate; titanium plate was used as cathode and a silver-silver chloride electrode in a 1 mol.L-1 KCl solution, the reference. The tests were performed using phenol solution in the presence of different concentrations of NaCl. The degradation of phenol and chlorinated byproducts were monitored by Gas Chromatography/Mass Spectrometry (GC/MS) for identification and quantification of compounds obtained at the end of the process according to USEPA Method 8270D. Results shown that, the rate of COD removal changed as a function of the NaCl concentration. After 30 min of electrolysis in the presence of 20 g.L-1 NaCl, 99.99% COD was removed from the solution. The concentration limit established by Brazilian Environmental Agency (CONAMA) of phenol in Class 1 saltwater, was obtained after 30 min of electrolysis of 100 mg.L-1 phenol at a fixed current density of 10 mA.cm-2, regardless the chloride concentration used. For chlorophenols a longer electrolysis time was necessary. After, 360 min, this concentration was below the limits established for discharge. The current efficiency (CE) and energy consumption (EC) of the process were calculated from the data of COD and the results shown that, the energy consumption decreased with increasing chloride concentration in solution.

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