Abstract
A di-azo dye, Congo Red (CR) was used as a model compound to investigate the degradation mechanism in hot compressed water (HCW). The unique properties of HCW facilitated the degradation efficiency without addition of any organic solvent. The influences of reaction time, temperature, initial dye concentration and amount of hydrogen peroxide (H2O2) on the degradation of CR and the removal of total organic carbon (TOC) from the product solution were investigated. The presence of H2O2 was found to enhance the degradation of CR. The results showed that the degradation yield could reach 99.0% with a solution of 100 ppm CR and 50 mM H2O2 at 150°C at the end of 60 min. Maximum conversion of the total organic carbon was recorded as 62.2%. Moreover, the effect of the presence of several co-existing negative ions such as SO4 2-, Cl-, CO32- were investigated. It was found that the presence of SO42- accelerated evidently the degradation of CR. The other chosen anions (CO32- and Cl-) had an inhibitory effect on the decolorization of CR. Finally, kinetic study was carried out and the order of the reaction was calculated as 0.37.
Highlights
During the last decades, contamination of surface and ground water resources by various pollutant residues has become one of the major challenges for the preservation and sustainability of the environment
The degradation of Congo Red (CR) as a model compound of diazo dyes was studied in hot compressed water without any organic solvent under various operating conditions by using an autoclave
In the presence of 20 mM H2O2 as an external oxidant, at 150°C, 99% of CR was successfully removed from the model dye wastewater at the end of 60 min
Summary
Contamination of surface and ground water resources by various pollutant residues has become one of the major challenges for the preservation and sustainability of the environment. Pesticides are among the most dangerous environmental pollutants because of their stability, mobility, capable of bioaccumulation and long-term effects on living organisms [2,3]. Removal of this kind of contaminants by adsorption [4,5,6,7], nanofiltration [8,9], using Fenton reagent [10], photo-catalytic degradation [11,12], biological treatment [13] and the combination of biological and photo-Fenton treatment [14] were widely studied. Ion exchange resins [16,17,18,19], membrane filtration [20,21], adsorption [22,23,24], electrochemical [25] and biological treatments [26,27] are some of successful techniques for the removal of heavy metal ions (lead, arsenic, nickel, etc.) [28]
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