Electrokinetic copper and iron migration in anaerobic granular sludge

The application of low-level direct electric current (0.15 mA cm ^-2) as an electrokinetic technique to treat copper-contaminated mesophilic anaerobic granular sludge was investigated. The sludge was obtained from a full scale UASB reactor treating paper-mill wastewater and was artificially contaminated by Cu(NO₃)₂ or CuEDTA ^2- with initial copper concentrations of 1000 mg . kg^-1 wet sludge. The effect of different electrokinetic cell layouts, pH and EDTA concentrations on the migration of copper and iron during electrokinetic treatment were evaluated. Both, the pH of the sludge cake or the copper complexation with EDTA significantly affected the migration direction of copper. In an 'open' cell (sludge cake in direct contact with air), the highest copper mobility was observed at pH 2.5 in both Cu(NO₃)₂ or CuEDTA^2- amended sludge. The highest copper accumulation was at the cathode (22 ± 2)% with CuEDTA^2- as contaminant. In a 'closed' cell (sludge cake not in contact with air), the highest accumulation was obtained for CuEDTA^2- at the anode and amounted to 4(± 0.5)% and 2(± 0.05)%, respectively, at a final pH of 4.2 and 7.7 in the sludge cake.