Treatment of high strength hexamine-containing wastewater by Electro-Fenton method

A novel Electro-Fenton (EF-Fere) method, applied H₂O₂ and electrogenerated ferrous ion, was investigated for treating the hexamine-containing wastewater. The performance of Fe²⁺ generation in the electrolytic system was first evaluated, including the factors of the cathode material, initial pH, initial ferric concentration (Fe(i)), and current density. When initial pH exceeded 2.5, the current efficiency dramatically decreased, which was due to the formation of Fe(OH)₃. Between 3000 and 10,000 mg/l of Fe(i), the initial current efficiency of Fe²⁺ generation was almost constant (85-87%), which dropped sharply to 39% at 1000 mg/l. In EF-Fere experiments, the COD removal efficiency attained above 94% after 5 h of reaction. The relationship between the temperature, dissolved oxygen, and COD was discussed. The changes in hexamine and its oxidation intermediates (methanol, formaldahyde, formate, ammonium and nitrate) during the reaction were also investigated. Three additional experiments using H₂O₂/Fe²⁺, H₂O²/Fe³⁺, and direct electrolysis were also conducted to treat the hexamine-containing wastewater for comparison. The results showed that the EF-Fere method was the most efficient.