Decoloration of azo dye methyl orange by a novel electro-Fenton internal circulation batch reactor

Abstract A novel internal circulation batch reactor (ICBR) was utilized to treat an azo dye pollutant methyl orange (MO) solution by the Electro-Fenton process, with graphite rods as the anodes and metal processing waste iron shavings as the cathodes. The MO decoloration efficiency reached 98.6 % for 0.08 g L–1 MO after an 18-min reaction under the optimal conditions of a pH=3.00, current density=0.90 mA/cm2 and Na2SO4 concentration=7.00 g L–1. A kinetic fitting analysis shows that the MO decoloration rule complies with the first-order kinetics model, and the rate constant reaches 0.329 min–1 under optimal conditions. The durability of the iron-shavings cathode was tested by decoloration of 5 batches of MO using the same cathode without allowing the regeneration process to proceed. MO decoloration efficiencies also reached as high as 95 % in the fifth batch 34 min into the reaction, even though the first-order rate constants decreased to 0.064 min–1. The iron-shavings cathode could also be reused by washing with 5 % (w/w) dilute sulfuric acid. Compared to the conventional square-shaped electrolytic batch reactor (SEBR), ICBR has the remarkable advantages of MO decoloration efficiency and energy conservation.