Electrocoagulation of simulated reactive dyebath effluent with aluminum and stainless steel electrodes

Reactive dyebath effluents are ideal candidates for electrocoagulation due to their intensive color, medium strength, recalcitrant COD and high electrolyte (NaCl) content. The present study focused on the treatability of simulated reactive dyebath effluent (COD_o = 300 mg/L; color in terms of absorbance values A_o,436 = 0.532 cm^-1, A_o,525 = 0.693 cm^-1 and A_o,620 = 0.808 cm^-1) employing electrocoagulation with aluminum and stainless steel electrodes. Optimization of critical operating parameters such as initial pH (pH_o 3-11), applied current density (J_c = 22-87 mA/cm²) and electrolyte type (NaCl or Na₂SO₄) improved the overall treatment efficiencies resulting in effective decolorization (99% using stainless steel electrodes after 60 min, 95% using aluminum electrodes after 90 min electrocoagulation) and COD abatement (93% with stainless steel electrodes after 60 min, 86% with aluminum electrodes after 90 min of reaction time). Optimum electrocoagulation conditions were established as pH_o 5 and J_c = 22 mA/cm² for both electrode materials. The COD and color removal efficiencies also depended on the electrolyte type. No in situ, surplus adsorbable organically bound halogens (AOX) formation associated with the use of NaCl as the electrolyte during electrocoagulation was detected. An economical evaluation was also carried out within the frame of the study. It was demonstrated that electrocoagulation of reactive dyebath effluent with aluminum and stainless steel electrodes was a considerably less electrical energy-intensive, alternative treatment method as compared with advanced chemical oxidation techniques.