Three-dimensional electro-Fenton system with iron foam as particle electrode for folic acid wastewater pretreatment

At the very first time, a three-dimensional (3D) iron foam was used as the particle electrode for folic acid (FA) wastewater pretreatment in the electro-Fenton (EF) process. In this work, the effects of key operating parameters, including the initial COD concentration, applied current, initial pH and iron foam dosage were optimized regarding the chemical oxygen demand (COD) and total nitrogen (TN). COD and TN removal percentage of FA wastewater reached 43.5% and 70.4%, respectively during 6 h electrolysis under the following optimal conditions: initial COD concentration of 10,000 mg/L, applied current of 300 mA, initial pH of 3 and iron foam dosage of 4 g. Regarding the main oxidant species in the proposed EF with iron foam particle electrode, (OH)-O-center dot and active chlorine were responsible for FA mineralization, confirming by the electron paramagnetic resonance (EPR) spectra of DMPO-(OH)-O-center dot. The kinetic analysis and mechanism study suggested that both electro-oxidation and electro-coagulation exited in the system. A possible FA degradation pathway based on the identification of by-products was proposed according to Liquid chromatography/time-of-flight/mass spectrometry results. In addition, BOD5/COD ratio improved from 0.22 to 0.44 after EF treatment coupled with toxicity reduction. In a word, EF with iron foam particle electrode was a feasible process for FA pretreatment.