Continuous electrochemical treatment of phenolic wastewater in a tubular reactor

Abstract

The electrochemical treatment of phenolic wastewater in a continuous tubular reactor, constructed from a stainless steel tube with a cylindrical carbon anode at the centre, was investigated in this study, being first in literature. The effects of residence time on phenol removal was studied at 25°C, 120 g l −1 electrolyte concentration for 450 and 3100 mg l −1 phenol feed concentrations with 61.4 and 54.7 mA cm −2 current densities, respectively. The change in phenol concentration and pH of the reaction medium was monitored in every run and GC/MS analyses were performed to determine the fate of intermediate products formed during the electrochemical reaction in a specified batch run. During the electrolysis mono, di- and tri-substituted chlorinated phenol products were initially formed and consumed along with phenol thereafter mainly by polymerization mechanism. For 10 and 20 min of residence time phenol removal was 56% and 78%, respectively, with 450 mg l −1 phenol feed concentration and above 40 min of residence time all phenol was consumed within the column. For 1, 1.5, 2 and 3 h of residence time, phenol removal achieved was 42%, 71%, 81% and 98%, respectively, at 3100 mg l −1 phenol feed concentration. It is noteworthy that more than 95% of the initial phenol was converted into a non-passivating polymer without hazardous end products in a comparatively fast and energy-efficient process, being a safe treatment.