Treatment of Reactive Black 5 by combined electrocoagulation-granular activated carbon adsorption-microwave regeneration process

Treatment of an azo dye, Reactive Black 5 (RB5) by combined electrocoagulation-activated carbon adsorption-microwave regeneration process was evaluated. The toxicity was also monitored by the Vibrio fischeri light inhibition test. GAC of 100 g L-1 sorbed 82% of RB5 (100 mg L-1) within 4 h. RB5-loaded GAC was not effectively regenerated by microwave irradiation (800 W, 30 s). Electrocoagulation showed high decolorization of RB5 within 8 min at pH0 of 7, current density of 277 A m-2, and NaCl of 1 g L-1. However, 61% COD residue remained after treatment and toxicity was high (100% light inhibition). GAC of 20 g L-1 effectively removed COD and toxicity of electrocoagulation-treated solution within 4 h. Microwave irradiation effectively regenerated intermediate-loaded GAC within 30 s at power of 800 W, GAC/water ratio of 20 g L-1, and pH of 7.8. The adsorption capacity of GAC for COD removal from the electrocoagulation-treated solution did not significantly decrease at the first 7 cycles of adsorption/regeneration. The adsorption capacity of GAC for removal of both A265 (benzene-related groups) and toxicity slightly decreased after the 6th cycle.