Ferrous ions (Fe2+) assisted air-bubble cavitation degradation of organic pollutants

Abstract

The ferrous ions (Fe2+) assistant air-bubble cavitation degradation of some organic dyes (Congo Red, Rhodamine B, Methyl Orange, and Methyl Violet) induced by air bubbles passing small glass balls was systematically investigated. Meanwhile, the influence of five operating factors, including air-bubbling time, FeSO4 ·7H2O amount, dye initial concentration, glass ball diameter, and gas flow rate, on the degradation of Congo Red dye were reviewed. Moreover, the degradation process of Congo Red is inspected by using UV–Vis, TOC, and HPLC techniques. It was found that the highest TOC removal ratio (81.42 %) was achieved under optimal conditions. On the other hand, the production and existence of ·OH radicals was testified through the oxidation of 1,5-diphenylcarbohydrazide (DPCI) forming diphenylcarbazone (DPCO). It can be inferred that the air-bubble cavitation induces ferrous ions to provide additional hydroxyl (·OH) radicals, which results in a rapid oxidation of organic dyes. Furthermore, the possible degradation process and mechanism were also discussed. All results demonstrate that this new degradation method has many advantages, such as high efficiency, energy savings, producing no secondary pollution, and being a simple device. Thus, it is expected to be feasible and promising as an advisable choice for the treatment of organic wastewater in the future.