Study On Degradation Of Quinoline Wastewater By Supercritical Water Oxidation

Industries increasingly generate complex N-containing organic wastewater,which is dangerous to the environment. Quinoline is chosen as a model compound,because it is non-biodegradable and contains heterocyclic nitrogen, which is highlyrefractory. Supercritical water oxidation (SCWO) is a forthcoming technology forthe treatment of wastewater containing non-biodegradable compounds. In this paper,the supercritical water oxidation of quinoline was investigated.The operating conditions of the process for SCWO was studied by the responsesurface methodology(RSM) and central composite design(CCD),a response surfacequadratic model was obtained based on experimental data. Additional experimentswere performed to check the model, the relative error was about5%, which showedthat the model can predict the results of the experiments.The suitable condition for the wastewater treatment was obtained based on thequadratic model, the suitable temperature, pressure, residence time and excessoxidation multiple were found to be441℃,25MPa,60s and2.48, respectively. Inthis condition, the TOC had met the wastewater discharge demand. Based on thesuitable condition, single factor experiments were used to analysis the effects oftemperature, pressure, residence time and excess oxidant multiple on the organicsremoval. The TOC removal was increased with higher temperature, the pressure hadsmall effect on the degradation of organics, longer residence time and more oxidantwere also benefit for the removal of TOC.The liquid and gas products were analyzed after experiment, the carbon ofquinoline was mainly oxidized into carbon dioxide and small amount of carbonmonoxide, nitrogen was mainly transformed into ammonia, nitrogen and littleN-containing compounds. During the experiments, improving the temperature wasbenefit for the generation of gas and ammonia, pressure had little effect on thecontent of products, prolonging the residence time and increasing the oxidant wereavailable for the conversion of carbon monoxide into carbon dioxide. At the suitablecondition,73~78percent of carbon were oxidized into carbon dioxide,12~15 percent of carbon were oxidized into carbon monoxide, and55~60percent ofnitrogen were changed into nitrogen.Utilizing the quantum chemical computation method based on the densityfunctional theory, the main path of nitrogen conversion was studied with the resultsof experiments.