Electrochemical degradation of anionic surfactants

Surfactants are the active cleaning ingredients in synthetic detergents used for all kind of washing. The most common surfactants in use in industrial and household detergents are of the anionic type such as the linear alkyl benzene solfonate (LAS). Even if they are more easily biodegraded than the highly branched alkyl benzene solfonate (ABS), their presence in waters favours the formation of stable and highly- difficult-to-separate emulsions that are becoming a pollution danger. Many papers have demonstrated that electrochemical technologies can be efficiently applied to the treatment of wastewater containing organic pollutants, however, up to now little attention has been paid to the possibility of applying electrochemical processes to the degradation of anionic surfactants. By means of electrochemical oxidation, pollutants can be completely mineralised by direct electrolysis using high oxygen overvoltage anodes such as PbO2 and boron-doped diamond or by indirect electrolysis, using chloride ions as an inorganic mediator of oxidation. Direct and indirect electrochemical oxidation has been used for the combustion of many synthetic solutions and industrial wastewaters. The aim of the present study was to study the electrochemical oxidation of a synthetic solution and of a real car wash wastewater containing anionic surfactants. The electrochemical treatment was performed by direct electrolysis, using a boron- doped diamond (BDD), and indirect electrolysis, generating in-situ active chlorine, using a Ti-Ru-Sn ternary oxide anode. In particular, the influence of such operating parameters as chloride concentration, current density and mass-transfer coefficient were studied for each electrode, in order to find the optimal conditions for the electrolysis. A comparison of the data obtained with the two electrode materials, each in its optimum experimental conditions, showed that faster sodium dodecyl benzene solfonate mineralisation was achieved during indirect electrolysis at the Ti-Ru-SnO2 anode. Even in the case of the treatment of a real car wash wastewater, mediated electrolysis at the Ti-Ru-SnO2 anode allowed faster COD removal