Improvement of the activated sludge treatment by its combination with electro Fenton for the mineralization of sulfamethazine

• Mineralization of sulfamethazine (SMT) solutions was investigated by means of a combined process.
• The combined process consisted in the coupling of electro-Fenton and a biological treatment.
• Electro-Fenton pretreatment led to total SMT degradation, while mineralization level was low.
• Two possible degradation reaction pathways for sulfamethazine during electro-Fenton were proposed.
• Biological treatment allowed a total mineralization of the electrolyzed SMT solutions.

A combined process coupling an electro-Fenton pretreatment and a biological degradation in order to mineralize sulfamethazine (SMT) was investigated. The electro-Fenton pretreatment of SMT was first examined and the intermediates products were identified for an initial SMT amount of 0.36 mM, after 1 h electrolysis at pH 3, 18 °C, 200 mA. 94.2% SMT was degraded but the level of mineralization remained low (6.5%), ensuring significant residual organic content for a subsequent biological treatment. Two possible degradation reaction pathways involving all the identified and quantified intermediates are proposed. In a second part, biological treatments with fresh activated sludge were performed to complete the mineralization of the electrolyzed solution of SMT, showing an increase of the mineralization yield with time duration of the pretreatment. For an initial SMT concentration of 0.2 mM, a ferrous ions concentration of 0.5 mM, at pH 3, 18 °C and 500 mA, the mineralization yield during the biological treatment increased as follows: 61.4, 78.8 and 93.9% for 0.5, 1 and 4 h pretreatment, confirming the relevance of the proposed combined process.