EFFECT OF ELECTROLYTES ON THE ELECTROCHEMICAL OXIDATION OF SYNTHETIC DYES

Textile industries produce large quantities of wastewaters containing significant amounts of toxic organic substances (mainly synthetic dyes) and other pollutants. The impact on the environment is large and strict limits have been applied recently. Most of the currently available treatment methods cannot treat effectively wastewaters containing synthetic dyes. Methods that are based on the production of solids are ineffective due to the high solubility of synthetic dyes. Even when solids are produced the final solid residue is toxic and should be handled with care. One alternative method is electrochemical oxidation, which has the potential to destroy the toxic organic dyes to less toxic or smaller ones that are biodegradable. In this work it has been applied on commercially available synthetic reactive dyes (blue, orange and red) at various initial concentrations (100, 200, 500 and 1,000 mg/L) and promising results were obtained. The kinetics of the process was studied for each of the above dyes; 50% of the color was removed after 20 min for all dyes and the final concentrations after 60 min were similar. The effect of the type of electrolyte was also studied. Analytical solutions of NaNO3, Na2SO4 and NaCl were used under similar conditions (electrolyte concentration, pH, applied Voltage and current intensity) and the results were compared. It was found that NaCl was much faster in colour removal for all three dyes used; 20 min were enough to remove the dyes when NaCl was used. However, the final concentrations of the dyes after 60-90 min were similar. Even high initial concentrations of the dyes (i.e. 1,000 mg/L) were treated fast and effectively. The method was proved effective for the removal of synthetic dyes from model solutions.