Combination of hydrodynamic cavitation with oxidants for efficient treatment of synthetic and real textile wastewater

In this study, the degradation of direct red 89 (DR89) dye from synthetic wastewater was assessed by lab-scaled hydrodynamic cavitation (HC) combined with different oxidants such as periodate (PI), persulfate (PS), and oxalic acid (OA). The degradation tests were carried out by combining the three oxidants in the absence of HC, and using HC with only one of the oxidants (HC/OA, HC/PS, and HC/PI) or with all combined (HC/PS/OA/PI). In all processes, the degradation constants followed first-order reaction kinetics, being the highest one that of the HC/PS/OA/PI process, equal to 2.01 x 10-1 min-1. The degradation of DR89 was affected by pH, initial dye concentration, and reaction time. The degradation efficiency increased when pH decreased obtaining the best results at pH 3.0 due to favorable conditions for the generation and persistence of radical species. The degra-dation of the dye improved with increasing dose of OA, PS and PI. The best results were achieved using dosages of OA, PS, and PI of 100.0, 125.0, and 150.0 mg L-1, respectively. The quenching experiments revealed the presence of center dot OH, SO4 center dot-, IO3 center dot, O2 center dot-, and 1O2 in the HC/PS/OA/PI process, while center dot OH, SO4 center dot- and IO3 center dot were the dominant responsible radicals. The rate constants of the individual processes were used to calculate the value of the synergetic coefficient of HC/PS/OA/PI process. At the optimum conditions, the calculated synergetic coef-ficient was 15.39. The effectiveness of the HC/PS/OA/PI process in the removal of color and COD from real textile wastewater was also investigated and exhibited the 96.23 +/- 1.92 % and 93.84 +/- 0.94 % reduction of color and COD after 70 min reaction time, respectively. The results showed that the combined process can be a useful technology for the treatment of textile wastewater.