Study On Oxidation Of Nitrogenous Organics In Supercritical Water

Supercritical water oxidation (SCWO) is a highly efficient organicwastewater treatment technology. When exceeding the critical point ofsupercritical water (Tc=374.3℃, Pc=22.05MPa), the water propertieschange immensely. For example, the water density and salt solubility valuesdecrease. Under supercritical condition, water has excellent transport propertyand high diffusivity so that oxygen, supercritical water and organiccompounds become miscible. In this study, the organic compounds werecompletely oxidized in a short time.In this paper, correlation coefficients between TC95, TN50and quantumchemical descriptors were analyzed. Finally, the theory was applied in SCWOpilot equipment research and development.The results indicate that with theincrease of temperature, TOC degradation efficiency of the19kinds ofnitrogenous organic compounds increased while the TOC value of theeffluent gradually reduced. When the temperature reached500℃, theorganics were degraded completely. In addition, the TOC degradationefficiency of all kinds of organics achieved99.00%except forp-dimethylaminobenzaldehyde, Melamine,1-Methylimidazole, Cyanuric acid,Methylthioninium chloride,1,10-Phenanthroline monohydrate. Based on theeffluent’s detection results, the value of nitrite-nitrogen (NO2-N) was verylow. However, ammonia was the incomplete oxidation product. The value ofammonia was still high even though under the reaction temperature of500℃.The correlation analysis results showed that qC-H+and qC-were the mostimportant factors for TC95and TN50. The electro-negativity of nitrogen atomsare stronger than that of the carbon atoms. Therefore, the electron cloud around the carbon atom will have a high affinity for the nitrogen atom, which is near to the carbon atom. With the increase of qC-,TC95and TN50increased, which meant that the organic compound was more difficult to degrade.The degradation experiments of industrial wastewater were conducted by a pilot scale SCWO equipment.5tons of wastewater could be treated per day. The experiments were conducted for three factors (COD concentration of influent, reaction temperature, residence time).The results showed that under the condition of adequate residence time and reaction temperature, COD degradation efficiency may reach99.00%when the COD concentration of influent ranged from10000mg/L to30000mg/L. Meanwhile, the color and odor improved greatly through the SCWO process. The GC-MS comparison results between the influent and effluent showed that there were15main kinds of organic compounds in the complex influent, which were degraded efficiently.The energy balance of SCWO pilot-scale system was also studied under various temperatures, residence time and COD concentrations. There was a simulated equation about electricity consumption, which is shown as below: It was used to estimate electricity consumption. The model was significant for reactor design and engineering budget.