Decolorization of reactive red 195 from aqueous solutions by soybean cake using adsorption, ultrasound and ultrasound-assisted adsorption

Many industries, especially the textile industry, are the main generator of dye-based pollution, and this case is a very important issue to be dealt with sensitively. In this study, decolorization of reactive dyestuff solution which is prepared under laboratory conditions by adsorption, ultrasound and ultrasound-supported adsorption processes is examined. In addition, effects of pH of solution, initial dyestuff concentration, adsorbent concentration, temperature and reaction time on decolorization efficiency are examined. Under constant conditions of initial dyestuff concentration of 250 mg L-1, adsorbent concentration of 2.0 g L-1, temperature of 20 oC, and four-hour reaction duration, decolorization efficiency was found as %88, %98 and %99.9 for the processes of adsorption, ultrasound and ultrasound-supported adsorption, respectively. Therefore, ultrasound was determined to able to be used in decolorization of reactive dyestuff. Tukey multiple comparison test (at %95 confidence interval) showed that there are important differences among sub-levels of the explanatory variables (p < 0.001). As a result of correlation matrix, a highly negative correlation was found between decolorization efficiency and initial dyestuff concentration (r = -0.54), while a highly positive correlation was found between decolorization efficiency and adsorbent concentration (r = 0.89) and temperature (r = 0.53). Also, there existed a correlation between decolorization efficiency and reaction time depending on the process type of interest. There was a highly positive correlation between decolorization efficiency and reaction time for the process of adsorption (r = 0.73), while there was a moderate positive correlation between them for the processes of ultrasound (r = 0.49) and ultrasound-supported adsorption (r = 0.48) (p < 0.001). Multiple non-linear regression (MNLR) models accounted for 89.6%, 93.3% and 85.1% of variation in decolorization efficiency as a function of (1) initial dyestuff concentration, process type, and reaction time, (2) adsorbent concentration, process type, and reaction time and (3) temperature, process type, and reaction time (p < 0.001).