Study On Treatment Of Organic Wastewater With Complex Components By Supercritical Water Oxidation

In the supercritical conditions (T>647.3K, P>22.12MPa), water is a nonpolar solvent which is able to dissolve oxygen and organic compounds in any proportion. The reaction species will be mixed fully under the medium of supercritical water, accelerating the reaction rate with oxygen and organic compounds. Supercritical water oxidation (SCWO) can efficiently decompose organic compounds into H2O and CO2in the ultrashort residence time, as a substantial promising route for clean and efficient decontamination of the aqueous organic wastes.In this dissertation, with the help of the hydrogen peroxide (H2O2) as an oxidant, the oxidation of dye wastewater, pyridine wastewater and coking wastewater under the supercritical water oxidation technique was studied. The main research contents and conclusions are as follows:(1) Oxidation of aqueous solution of C.I. Disperse Blue56(DB56) by SCWO was studied in a continuous-flow reactor. The result indicates that the degree of the oxidation of organics increases, as the temperature, pressure, residence time and oxidant concentration increase.90%and99%of CODCr and color removal efficiency was achieved at temperature390℃, pressure25MPa, residence time18.75s. oxidant dosage n=3. Near the critical point, the density of water decreases severely as the temperature increases, and then the residence time decreases drastically owing to the increased specific volume, thus the removal of CODCr (Chemical Oxygen Demand) decreases, when the reaction temperature is over390℃. The trend of dye removal with the change of the operational factors consists with that of CODCr removal; however, the value of dye removal is higher.(2) Decomposition of pyridine wastewater by SCWO was investigated, comparing the results with. that of the dye wastewater. With the same experimental conditions, the decomposition efficiency is lower to oxidize pyridine than dye wastewater. The same trend with different operating factors appears between pyridine and dye wastewater.60%of pyridine conversion was achieved at temperature420℃, pressure25MPa, residence time12.78s oxidant dosage n=5. As the reaction temperature increased, the density of water decreases and thus the residence time decreases, but oxidation of pyridine needs shorter residence time, resulting in little influence to the decomposition efficiency. (3) A certain percentage of aniline, quinoline,4-chlorophenol was mixed as the coking wastewater. The oxidation of the coking wastewater and N-fraction of aqueous samples was studied.80%of CODCr removal efficiency was achieved by supercritical water oxidation. The result indicates that nitrogen mainly exists in the form of nitrate and ammonia. With the increases of temperature, pressure and oxygen concentration, the concentration of nitrate decreases and the concentration of ammonia increases. The change of the residence time influences faintly on the N-fraction of liquid product. The nitrite of liquid product was not detected.(4) According to the characteristics of the experimental apparatus, the exponential form of oxidation kinetic equation was corrected. The global rate expression was regressed from the complete set of data for the oxidation of DB56, pyridine and coking wastewater. Analysing the reaction process according to the kinetic equation, it indicates that the results can be well predicted by the model.