Electrooxidation of nonylphenol ethoxylate-10 (NP10E) in a continuous reactor by BDD anodes: optimisation of operating conditions

Abstract

Electrooxidation (ELOX) of synthetic and real wastewater containing nonylphenol ethoxylate-10 (NP10E) surfactant as a model pollutant was investigated using a boron-doped diamond anode (BDD) in a continuous reactor in the presence of Na2SO4 or NaCl supporting electrolyte. Response surface methodology (RSM) with there factors and five coded levels (Central Composite Design, CCD) was used to optimise the continuous ELOX process performing 17 runs for each supporting electrolyte type. Individual and interactive effects of process variables such as initial pH of synthetic wastewater, current density and electrolysis time on NP10E electrooxidation were investigated in terms of COD, TOC, and NP10E removal efficiencies. It was found that NP10E to be more efficiently electrooxidized when NaCl was used as the supporting electrolyte. Under the optimal experimental conditions (initial pH 8, current density of 250 A/m(2) and electrolysis time of 45 min) for electrooxidation of synthetic wastewater, the removal efficiencies were 91.6%, 94.3% and 85.3% with the operating cost of 0.90 US$/m(3) for COD, TOC, and NP10E, respectively. In the studies conducted with real wastewater, obtained results were very close to these results. And also, kinetic studies were performed to find the reaction rate coefficient at the optimum conditions. Based on the type of supporting electrolyte the COD removal rates were fitted first order and zero-order reaction kinetic rules for Na2SO4 and NaCl, respectively.