Activated Carbon Catalyzed Persulfate Oxidation Of Organic Contaminations In Water

Persulfate (PS) oxidation is a recently emerging technology for the pollution control. Produced by activated PS, the sulfate free radical, SO₄^-·, a powerful oxidant, can degrade most of the organic compounds. The study of activation method is a hot issue. There are unitary activation methods, such as heat, ultraviolet light, transition metal ions, zero-valent metal Fe⁰, and the multiplex activation technologies including PS combined with UV/TiO₂, dual oxidant system, and hybrids of activation methods.In this study, PS oxidative degradation of organic pollutants (azo dyes: Acid Organge 7, Reactive Black 5 and Reactive Brilliant Orange) in an aqueous solution was studied in the presence of suspended granular activated carbon (GAC). Moreover, the mechanism of organic matter degradation in the GAC/PS combined system is also discussed. The technology in this work is carried out under atmospheric pressure and at ambient temperature, mild reaction conditions, no external power, no secondary pollution, no sludge and the removal of biorefractory organics is high, indicating that the technology of GAC induced PS has broad application prospects in the field of water treatment. Specific studies and results are as follows:1) It was observed that there existed a remarkable synergistic effect in the GAC/PS combined system. Higher PS concentration and GAC dosage resulted in higher AO7 degrading rates. In the GAC/PS combined system AO7 had a good decolorization whether the concentration was high or low (20 mg/L 500 mg/L). Near-neutrality was the optimal initial pH of reaction solution. AO7 had not only a good decolorization, but a good mineralization. The decomposition of PS followed a first-order kinetics behavior both in the presence and in the absence of AO7. In addition, there also existed a remarkable synergistic effect for degradation Reactive Black 5 and Reactive Brilliant Orange in the GAC/PS system.2) The adsorption and catalysis processes happened at the same time in the GAC/PS combined system. So it was necessary to study the interaction between adsorption and oxidation in the combined system. The results showed adsorption had an adverse effect on AO7 degradation because the loading dye molecules on the GAC surface reduced the active surface sites available for the activation of PS. As a catalyst, GAC can be reused for four times. For every reuse cycle, AO7 removal efficiencies gradually decreased. However, with the oxidant concentration increased, the extent of the deactivation of GAC decreased. The adsorption capacity of reused GAC decreased as the reuse-time increased. The surface oxygen function groups determinated by Boehm's titration method, the surface morphology by scanning electron microscopy (SEM) and the chemical composition by energy disperse spectroscopy (EDS) analysis of GAC changed very little before and after reuse. Therefore, the reason leading to the deactivation of GAC could be that adsorption took up the active sites, thus reducing PS's opportunities to contact with the surface of GAC.3) Compared with the only PS oxidation system or the only GAC adsorption system, the GAC/PS combined system can induce AO7 degradation more significantly. Three radical scavengers (MA, TBA, and phenol) were used to determine the dominant active spices generated in the GAC/PS system. Sulfate free radical SO₄^-·or hydroxyl radical·OH, which were produced by GAC catalyzed PS oxidation, played an ipportant role in the organic compound degradation. It was observed that the course of AO7 degradation by the GAC/PS system possibly didn't occur in the liquid phase, but the porous bulk or the boundary layer on the external surface of GAC granules.4) As a catalyst, GAC can be reused for several times, so we designed continuous operation system for the GAC/PS system. The catalytic properties of GAC in the sequencing batch continuous system hardly changed after four times'operations. AO7 removal efficiencies gradually decreased in the direct drainage continuous system. However, the GAC can be reused after regeneration by high concentration PS solution and the removal efficiencies on organics are a little inferior than the one before.