Treatability of a simulated spent disperse dyebath by chemical and electrochemical processes

Electrocoagulation (EC) using aluminum (Al) and stainless steel (SS) electrodes was investigated for color and chemical oxygen demand (COD) removal from a simulated spent disperse dyebath. EC was optimized for electrolyte (NaCl) concentration (750-3000 mg/L), current density (9-87 mA/cm²), and initial pH (3.5-11.5). Optimum EC conditions were established as 2,500 mg/L NaCl, pH_o = 7.0 and 44 mA/cm² for 100% color and 58% COD removals using Al electrodes (total treatment time = 30 min), whereas 100% color and 45% COD removals were obtained for 2,000 mg/L NaCl, pH_o = 7.3 and a current density of 44 mA/cm² when SS electrodes were employed for a 60-min treatment. EC results were compared with color and COD removals achieved via coagulation with alum, ferrous sulfate, and ferric chloride at varying doses (200-2,000 mg/L). Alum was more effective in color (100%) and COD (64%) removals than ferrous sulfate and ferric chloride. The amount of sludge formed during EC using SS electrodes was approximately 10 times less than the sludge produced during EC with Al electrodes, whereas electrical energy requirements to achieve 100% color and 50% COD removals were 10 and 30 times higher, respectively, when SS electrodes were employed for EC.