Anionic surfactants oxidation using AOPs and a novel “IN-FOAM UV/AIR OXIDATION” process

This paper presents some results of an experimental investigation of the possibility of using an “in-foam UV/air oxidation” process for the degradation of anionic surfactants. In this process, only the foam generated by bubbling air through the surfactant solution is exposed to the UV-C light, followed by recirculation to solution using a positive displacement pump.
The developed process, tested for sodium dodecylbenzenesulfonate and sodium dodecylsulfate 0.3-0.5 mM aqueous solutions seems to be promising, even compared with advanced oxidation processes such as UV/H2O2 , depending on photosensitizer dose.
Based on the analysis presented in this article the “in-foam UV/air oxidation” process has surprisingly good performances related to both surfactant concentration (primary degradation) and chemical demand (mineralization), but is limited by the lowest useful foaming concentration. The foam acts as a support for photochemical reactions, as it concentrates the surfactant to a high area interface, where it is exposed to the UV light and oxygen. By contrast, when only the solution is exposed to UV light, the “in-solution UV/air oxidation” process, the efficiency is low and, as expected, higher for the UV-absorbing aromatic compound sodium dodecylbenzenesulfonate. The “in-foam UV/air oxidation” process can be used as a pretreatment before biological aerobic treatment of clear waste water containing surfactants and is also an interesting research alternative for the oxidation of other organic compounds. This process can be refined by adding phosensitizers.