Assessment of several advanced oxidation processes applied in the treatment of environmental concern constituents from a real hair dye wastewater

Currently, little information is available regarding the presence of compounds from raw hair dyeing wastewater. It is known that the most commonly commercial formulations contain components with toxic properties and some by-products may also be mutagenic and carcinogenic. Indeed, virtually no studies can be found in the literature dealing with the treatment of such effluents and identification of environmental concerning substances, such as p-phenylenediamine, resorcinol and Bandrowski's base. The present work sought to evaluate the treatment of real hair dyeing effluent through different combinations of advanced oxidation processes including ozonation (O-3), ozone/UV-C (O-3/UV), ozone/photoelectrocatalysis (O-3/PEC), O-3/UV/H2O2 and O-3/PEC/H2O2. O-3/PEC/H2O2 combination provided almost complete mineralization while ozonation promoted less than 50% after 90 min of treatment. HPLC analysis confirmed the presence of p-phenylenediamine, resorcinol and Bandrowski's base in the raw effluent, which were completely removed in less than 5 min of treatment through the application of the combined O-3/PEC/H2O2 process. A figure of merit, the electric energy per order, was used to compare the different methods, showing that O-3/PEC/H2O2 provides lower energy consumption and higher mineralization, and could thus be an efficient option for wastewater treatment.