Efficiency of the heterogeneous catalyst from electrocoagulation sludge for the removal of methylene blue in the presence of persulfate.

Persulfate activation by heterogeneous catalysts based on transition metals is of interest in textile effluent treatment processes. Thus, iron-rich electrocoagulation sludge has been thermally treated to obtain new catalysts. The characterization of this catalyst by X-ray diffraction revealed the presence of FeAl2O4 nanoparticles active in the decomposition of persulfate into sulfate radicals (SO4•-). The efficiency of catalyst/persulfate was monitored during the methylene blue (MB) solution discoloration. The effects of temperature, pH, initial MB concentration, catalyst dose and persulfate dose were also studied. MB removal catalytic activity showed around 94% discoloration and 45.7% TOC reduction after 180 minutes batch reaction at pH = 4.0 (catalyst dose: 0.5 g/L, persulfate dose: 1 g/L; initial MB concentration: 20 mg/L). This catalyst reuse further confirmed its catalytic potential as a discoloration rate of about 82.45% was obtained after five cycles. The biodegradability monitoring measured by the carbon oxidation state (COS) has revealed a remarkable and continuous degradation of organic compounds. The EPR tests revealed that this catalytic reaction generates the radical species responsible for the degradation of MB. Finally, these results show that this catalyst from the thermal activation of electrocoagulation sludge is capable of decomposing persulfate to degrade bioresistant compounds such as textile dyes.