Dye wastewaters treatment using batch and recirculation flow electrocoagulation systems

An electrocoagulation (EC) process was employed to remove the Reactive Black 5 (RB5) dye from aqueous solutions using batch-stirred and recirculation flow reactor configurations. Different operating conditions, such as current density, initial pH value, initial dye concentration, sacrificial anode materials and stirring rate were tested with the synthetic wastewater in order to optimise the treatment. The best operating conditions achieved for both systems were: current density of 16 mA cm− 2, initial pH of 6, 100 mg L− 1 of RB5 and Al anodes, as well as 800 rpm for the batch-stirred setting. These parameters, at the batch-stirred EC system, led to 76% and 97% of decolourisation after 45 and 120 min of operation, with an energy consumption of 5 and 14 kWh m− 3, respectively. Similar colour removals were achieved for the recirculation flow system in 10 and 120 min, requiring 2 kWh m− 3 and 22 kWh m− 3 of electrical energy, respectively. The behaviours observed in each one of the EC systems (− batch and -recirculation flow) are related to the way how the liquid was mixed and the location where samples were taken. In the batch-stirred system, a real textile wastewater was also treated applying Al or Zn anode materials. Results clearly show that these two EC configurations are alternatives to depurate effluents containing dyes, since they guarantee the legal limits values so that a treated wastewater can be discharged into aquatic ecosystems.