Removal of 2,4-dichlorophenol and pentachlorophenol from aqueous media by electrochemical process

Chlorophenols are persistent toxins in the natural environment. In this investigation, 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP) in aqueous media were degraded using an electrokinetic process (EK) and an electro-Fenton process (EF) using stainless steel and graphite as the anode and cathode, respectively. Chlorophenols were degraded via direct electrolysis at the surface of the electrode in the EK process. However, in the EF process, the degradation mechanism includes direct electrolysis and oxidation by hydroxyl radicals. The optimal conditions were a current density of 0.75 mA/cm2 and an air flow of 0.7 l/min at pH 4. Under the optimal conditions, the 2,4-DCP and PCP removal rates in the EF process were 80.18 and 64.03 %, respectively. The mineralization efficiencies of 2,4-DCP and PCP were 78.23 and 75.77 %, respectively. The results of dechlorination reveal that almost all of the chlorines were released, but some were retained in the intermediates. The dechlorination efficiency revealed that the EF and EK4 processes two chlorines from 2,4-DCP. They released four or five chlorines and four chlorines from PCP, respectively. The kinetic results provide evidence of pseudo-first degradation. The rate constant (kcp) declined as pHi was increased from 4 to 10. The kcp values reveal that the pH is an important factor that affects the degradation efficiency in the electrochemical process.