Peroxi-coagulation of aniline in acidic medium using an oxygen diffusion cathode

A novel electrochemical method for wastewater treatment, called peroxi-coagulation, is presented in this paper. Degradation of aniline in acidic solution of pH similar to 3 has been studied using this method. Electrolyses were performed in an undivided cell with an Fe anode and a carbon polytetrafluoroethylene O-2-fed cathode which continuously electrogenerates H2O2. The anode dissolves yielding Fe2+ and Fe3+. This last ion gives a precipitate of hydrated Fe(III) oxide. Aniline and its intermediates are oxidized mainly by reaction with OH., which is produced from Fenton's reaction between electrogenerated H2O2 and Fe2+. Competitive coagulation of oxidation products with the hydrated Fe(III) oxide precipitate also occurs. These processes allow a fast and almost complete total organic carbon removal for aniline solutions in short time electrolyses. The method has higher decontamination power than other electrochemical treatments tested, such as electrocoagulation with a graphite cathode, and electro-Fenton and photoelectro-Fenton with a Pt anode. Benzoquinone, nitrobenzene, NH4+, and NO3- were detected in electrolyzed solutions. Precipitates contain coagulated organics with a major proportion of nitrogen-containing compounds. A pathway for aniline peroxi-coagulation involving these species is proposed.