Electrochemical conversion of phenolic wastewater on carbon electrodes in the presence of NaCl

Abstract

The electrochemical conversion of highly concentrated synthetic phenolic wastewater was studied on carbon electrodes in a batch electrochemical reactor. The effects of reaction temperature, electrolyte concentration, current density and initial phenol concentration on phenol conversion were elucidated. The wastewater was synthetically prepared and used in reactions carried out generally at 25 °C with an initial phenol concentration of 3500 mg dm⁻³. Although current density increased, phenol conversion% and initial phenol conversion rate did not increase correspondingly above 35 °C and an electrolyte concentration of 90 g dm⁻³. As the voltage values applied were increased, the increasing current density resulted in fast phenol conversion. Kinetic investigations denoted that overall phenol destruction kinetics was of zero order with an activation energy of 10.9 kJ mol⁻¹. Under appropriate conditions, phenol was completely converted within 15 min for an initial phenol concentration of 98 mg dm⁻³ while 8 h was required to gain 95% conversion using 4698 mg dm⁻³. Solid polymeric materials were produced at initial phenol concentrations above 500 mg dm⁻³ using the appropriate current density. In the reaction medium, only mono‐, di‐ and tri‐substituted chlorophenols were formed and 100% of all species were either oxidised or contributed to the formation of a polymeric structure. Almost all of the phenol loaded to the reactor was converted into non‐passivating polymeric products, denoting a safe and easy method for the separation of phenol.© 2001 Society of Chemical Industry