The Study On Degradation Of Organic Pollutants Adsorbed On Activated Carbon And Regeneration Of Activated Carbon By DBD Plasma

As traditional and emerging water treatment methods, respectively, activated carbon (AC) adsorption and dielectric barrier discharge (DBD) plasma technologies attract the extensive attention of scholars from different countries. Further studies on these two technologies find that AC adsorption simply transfers pollutants from one phase to another phase and does not remove the pollutants in essence, and the spent AC also needs to be regenerated for reuse. However, current AC regeneration methods exist many disadvantages. Although DBD plasma can degrade pollutants in wastewater effectively, high energy consumption limits its industrial applications. To solve these problems, and extend industrial applications of DBD plasma technology in wastewater treatment, an integrated AC adsorption and DBD plasma process is adopted for the treatment of refractory organic pollutants in this paper. Two procedures simultaneously are achieved:One is that the pollutants adsorbed on AC are degraded; the other is that AC is regenerated by DBD plasma. The following works are carried out and main results are summarized as follows:1. An AC packed DBD reactor for the pollutants treatment is designed. Through investigating the controlling factors (such as dielectric materials, dielectric thickness, gas gap between two electrodes and AC) that effect discharge characteristics of reactor, the optimal structure parameters of reactor are obtained. The effects of DBD plasma on morphology, microcrystalline structure and N2 adsorption capacity of virgin AC are also investigated in this optimal reactor. The result shows that plasma has etching behavior to AC surface, but has no significant effect to crystal structure of AC. N2 adsorption capacity of AC after plasma treatment under various gas atmospheres is different.2. By investigating the effects of condition factors (such as discharge voltage, power frequency, gas kinds and gas flow rate) on degradation efficiency, the decomposition of pentachlorophenol (PCP) on AC by DBD plasma is studied. The results indicate that with increasing of discharge and power frequency degradation efficiency of PCP on AC increases. The treatment effect of O2 as the carrier gas is better than that of N2 and air as carrier gas. While gas flow rate and treatment amount of AC has an optimal value, respectively. The higher is water content of AC, the better is degradation efficiency of PCP. In the investigation of PCP degradation process, AC regeneration feasibility by DBD plasma is also studied. The results indicate that DBD plasma can be used for the regeneration of AC, and can achieve high regeneration efficiency.3. Identification of intermediates is accomplished by some analysis tools, such as thermal gravimetric (TG), energy-dispersive X-ray spectrometer (EDX), Fourier transform-infrared spectroscopy (FT-IR) and gas chromatography/mass selective (GC/MS), and the degradation mechanism of PCP is speculated. The PCP is dechlorinated and dehydroxylated to chlorinated phenols (such as TetraCP, TriCP, DiCP) and chlorinated benzene (such as 4-chlorophenyl, 3-chlorobenzene) by DBD generated high energy electrons and active species at first, and then the dechlorinated or dehydroxylated products are further degraded into organic small molecules (such as acid, aldehyde or ketone), H2O and CO2 by·OH and O3.4. Another investigation is performed for the regeneration of AC exhausted with acid orange II (AO7). The efficiency of this procedure is analyzed by determining the rate and amount of AO7 adsorbed in successive adsorption/DBD plasma regeneration cycles. Although the regeneration efficiency decreases with the adsorption/regeneration cycle numbers increases, the adsorption rate and capacity of AC can maintain relatively high levels. Effects of this regeneration on the structural properties,.surface chemistry and the AO7 adsorption capacities of AC samples are examined. It is found that the decreases of AC adsorption capacity are resulted from the change of pore size distribution and surface chemistry, and residue on AC. Energy consumption analysis indicates that AC regeneration by DBD plasma is a viable regeneration technology, and has extensive industry application prospects.