电解诱发结晶对尿液废水中磷和钾回收的强化效应及其作用机制

Source separation of human urine helps to enhance the removal of N and P and the nutrient recovery from municipal wastewater. The precipitation of magnesium potassium phosphate hexahydrate (MPP) has been considered as a feasible approach to simultaneously recover P and K from source-separated urine. However, the co-precipitation of magnesium sodium phosphate heptahydrate (MSP) was found to be a bottleneck for further application of the MPP precipitation process. A novel approach for initiating the MPP precipitation via electrochemical dosing of Mg source is proposed and this project aims to investigate the mechanisms of the new precipitation process. Lab-scale experiments will first be conducted to study the characteristics of electrode reactions and the formation of anode passivation in the electrolytic cell with Mg anode. Then, batch experiments will be conducted to study the enhancement of nutrient recovery and the influences on the co-precipitation of MPP and MSP in two scenarios, i.e., recovering P and simultaneously recovering P and K from source-separated urine. Effects of anode passivation on the electrochemical precipitation process will also be evaluated. Further, the interactions of electrochemical Mg dosing and co-precipitations will be investigated based on the theories of electrochemistry and thermodynamics and kinetics of precipitation. Based on the studies above, a dynamic model coupled with electrochemical process and precipitation process will be established and the mechanisms will be revealed through model calculations. Process control measures for co-precipitations will finally be proposed for optimizing the simultaneous recovery of P and K from source-separated urine. The successful implementation of this project will provide theoretical basis and technical support for further application of urine source-separation.

尿液废水的分离式收集及其资源化有助于促进于污水中氮磷的深度减排和和营养元素的回收。通过磷酸钾镁反应结晶法可以同步回收尿液废水中的磷和钾资源，然而，磷酸钠镁共结晶却成为这一资源化技术应用的瓶颈问题。基于此，本项目提出一种利用镁阳极电解诱发磷酸钾镁反应结晶的方法控制磷酸钠镁共结晶，并着重探索其作用机制。项目中，研究镁阳极电解池电极反应特性，结合仪器检测手段分析镁阳极表面钝化膜的形成特征；分别以磷回收和磷钾同步回收为目标，研究电解诱发结晶对尿液废水中磷和钾回收的强化效应、对磷酸钾镁—磷酸钠镁共结晶的作用效果，分析阳极钝化对电解诱发结晶的影响；着重结合电化学、反应热力学和反应动力学理论探索电解过程与共结晶过程的相互作用关系，通过动态耦合模型的构建和模拟揭示电解诱发结晶的协同作用机制，分析共结晶的调控方案，实现对尿液废水中磷和钾的同步最优回收，为尿液废水资源化处理技术的发展提供理论基础和技术支撑。

尿液废水中磷和钾的同步回收可以提供一种磷钾肥料，本项目提出一种镁阳极电解促进磷酸钾镁反应结晶的方法，旨在降低磷酸钠镁结晶对磷酸钾镁结晶的抑制作用，提高钾的回收效率。研究结果表明，电解诱发结晶过程中，脱氨尿液中磷的回收率一直上升，而钾的回收效率则通常先上升后下降，磷和钾的最优回收不同步。初始pH值、尿液稀释度、电流密度、面体比和极板间距是电解诱发结晶的重要影响因素，通过黄水稀释度、电流密度和面体比的控制可以实现磷和钾的同步最优回收。在未加酸的条件下，体系中的pH未得到控制，钾离子的去除率会出现下降的拐点。在加酸的条件下，体系中的pH得到控制，钾离子的去除率得到优化，在电解3 h之后，钾离子的去除率可以达到60%。对镁电解释放量和20 mA/cm2加酸优化钾的回收试验进行了模型模拟，模拟的结果基本上是吻合的，可以对电解诱发结晶的过程特征进行模型模拟。通过SEM电镜的结果分别分析了1 mA/cm2、20 mA/cm2条件下获得的固体，在通过对比图片可以发现，在不同的电流密度下产生的固体样品其中基本都含有磷酸钾镁，磷酸钾镁是钾回收的一种主要途径，磷酸钠镁结晶得到了抑制。