城市污水脉冲电吸附深度脱氮技术与机理研究

Reduce the concentration of pollutants such as TN, ammonia nitrogen so that the effluent achieved level A standard of municipal sewage plan，is currently one of the problems in Upgrading and Reconstruction of Wastewater Treatment Plant.The removal of pollutants in ionic state,such as ammonia nitrogen, nitrate in wastewater by electric adsorption method is beyond doubt,.and has been applied.In this paper,pulsed switching power supply was creatively used in electric adsorption,aims to enhance the purifying effect, reduce energy consumption.Typical effluent from municipal sewage treatment plant was as treatment object, removal rate of ammonia nitrogen, TN, TP, TDS and COD was as criterion,and the effects of nitrogen concentration, organic matter, electrolyte, pH value, temperature and pulse frequency, duty cycle, electrode voltage, current density, electrode spacing and other factors on the adsorption process were studied.On this basis, pulse square wave current was used to eliminate the intrinsic dipole polarization of water molecules which was caused by external electric field , the concentration polarization in plate - solution interface, so as to reduce the resistance of ion migration and ion mass transfer. It was also studied that , average current density of the plate was improved by periodically charge and discharge of the capacitor structure, which was caused by on-off characteristic of pulsed switching power supply. Molecular dynamics simulation method was used to dissect the mechanism of pulse current to improve the electric adsorption process.

降低氨氮、总氮等污染物浓度使出水达到城市污水处理厂一级A标准或资源化再用，是目前污水处理厂提标改造技术难题之一。电吸附对水中氨氮、硝态氮等呈离子态的污染物去除是毋庸置疑的，且已得到一定的应用。本研究开创性的将脉冲开关电源应用于电吸附中，目的在于强化净化效果，降低能耗。将以典型的城市污水处理厂出水为处理对象，以氨氮、TN、TP、TDS及COD去除率等为判据，通过试验研究废水中氮素浓度、有机物、电解质、pH值、温度及脉冲频率、占空比、电极电压、电流密度、极板间距等因素对电吸附过程的影响。在此基础上探讨用脉冲方波波形电流来消除外电场导致的水分子固有偶极距取向极化及削弱极板-溶液界面浓差极化，从而减小离子迁移传质阻力的规律；研究通电-断电特性，引起电吸附类电容器结构周期性充、放电，提高极板平均电流密度的机理；利用分子动力学模拟方法深层次剖析脉冲电源对电吸附过程改善的机制。

目前要去除生化处理后几乎无生物可利用碳源废水中的氮素等污染物尚无成熟、经济可行的技术工艺，我国城镇污水处理厂提标改造急需解决这一技术难题。本研究创造性的将脉冲开关电源应用于电吸附过程中，利用间歇性通断直流电的脉冲电源来提供外电场，研究以典型的城市污水处理厂的出水为处理对象，以NH3-N、NO3-N的去除率等为判据，通过试验研究废水中污染物性质、氮素浓度、电解质、pH值、温度及脉冲频率、占空比、电极电压、极板间距等因素对电吸附过程的影响，并与常规直流电吸附进行比较。采用了分子动力学模拟，构建了直流电吸附和脉冲电吸附的体系，结果表明，在直流电吸附中，电极板/溶液界面间的氢、氧原子的排列方向更为固定，在脉冲电吸附下，则更为随机。正是因为脉冲电流的间歇性通断特性，极大的削弱了水分子偶极矩的取向极化效应，使得水分子偶极矩的取向趋向于随机化。离子在脉冲电场的作用下，离子水化层和水合半径更小，向电极迁移的过程中，所要克服的能垒要小于直流电场，从体系势能变化中，也侧面佐证了此观点。但并不是所有频率的脉冲电场的吸附效果都优于直流电场，针对不同离子，最优脉冲频率有其特征性。通过对不同电场下阴阳离子的竞争吸附的实验，验证了分子动力学模拟结果里关于H和O原子排列取向及削弱水化层的结论。结合电解质溶液理论，利用数学模型求解的方法，从理论上，分析脉冲电场的频率对离子和水分子的影响。结果表明，针对离子，在Debye-Huckel理论中，可将溶液中的离子分布看作由若干个离子氛组成；在脉冲电场的作用下，离子氛内的中心离子做周期性运动，以中心离子从离子氛内移出的幅度及对溶液的扰动为判据，当脉冲电场的一个通电周期内，中心离子恰能迁移到离子氛的边缘，即一个离子氛半径，此时达到对溶液的最大扰动，同时离子的迁移速率达到最大。据此面上项目资助，项目主持人共培养了4名博士研究生、2名硕士研究生，且发表了10篇SCI论文、3篇中文核心论文和1个发明专利。