Influence of some operating parameters on electro-oxidation of phenol using boron doped diamond anode and graphite cathode

The influences of current density, initial pH, initial phenol concentration and Na₂SO₄ electrolyte dosage on electro-oxidation of 100-1000 mg L^-1 phenol using Boron-doped Diamond (BDD) anode and graphite cathode were investigated. The evolutions of phenol and its oxidation byproducts were monitored with HPLC and GC-MS instruments. Removal efficiencies of phenol, Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD) were found to be mainly influenced by initial pH and initial phenol concentration with current density and Na₂SO₄ dosage having less significant effects. Complete oxidation of phenol was achievable under acidic and neutral pH regardless of initial phenol concentration; while under basic pH, accumulation of intermediary byproducts severely hindered the oxidation of 100 mg L^-1 phenol. Effective electro-oxidation of phenol was kinetically controlled process by direct oxidation process mediatedby the electro-generated hydroxyl radicals (OH') produced at the BDD anode surface. The evolutions of TOC, COD and phenol oxidation byproducts suggests initial pH and initial phenol concentration dependant pathways from which effective phenol oxidation been initiated by speciation molecules and subsequent generation of aromatic intermediates which were further converted to aliphatic acids. The final step in the pathway involved the destruction of the aliphatic acids to CO₂.