煤化工废水零排放系统反渗透过程的水质变化特征

Water quality transformation during the RO processes in the zero-liquid discharge system for coal chemical wastewater treatment

反渗透(RO)系统的稳定运行是煤化工厂废水实现零排放的关键。以我国北方某煤化工厂废水零排放(ZLD)系统为对象,重点分析多级RO过程中溶解性有机物(DOM)的变化特征,明确关键有机物的组成,并评价ZLD系统的运行特征与效能。结果表明,预处理可有效降低废水硬度,其他离子与污染物主要在RO阶段去除。废水中DOM主要以芳香蛋白类物质、腐殖质类物质和微生物代谢产物(SMP)类物质为主。预处理阶段对SiO_(2)的混凝去除效果较差(25.40%),RO进水SiO_(2)浓度较高,两级RO过程和高效反渗透段(HERO)对SiO_(2)的浓缩倍数分别为5.36/3.83,存在较高的膜面Si污染潜势。中水RO阶段有效截留腐殖质类和蛋白质类物质,而浓水RO阶段对色氨酸和SMP的去除效果较差。硅与有机物污染是RO过程的主要问题,因此,需强化预处理阶段有机物和硅的去除、优化药剂投加策略,加强对DOM和微生物的控制,进而实现系统运行效能的提升并减缓膜污染。

The long-term stability of the reverse osmosis(RO)system is crucial for achieving zero-liquid discharge of the coal chemical wastewater.This study focused on a zero-liquid discharge(ZLD)project located in northern China.The variations of the dissolved organic matter(DOM)during the multiple RO processes were investigated with a goal to identify the key organic compounds and evaluate the operational features and performance of the ZLD system.The results showed that the pretreatment could effectively decrease the hardness of wastewater,the removal other ions and pollutants mainly occurred at RO stage.The dominant DOM were aromatic proteins,humic substances,and soluble microbial metabolisms(SMP).Poor coagulation removal of SiO_(2)occurred at the pretreatment stage,and the removal efficiency was only 25.40%.SiO_(2)was mainly concentrated during RO processes,and the concentration factors at the 2nd-stage RO and high-efficiency reverse osmosis stage(HERO)were 5.36 and 3.83,respectively,indicating a high Si contamination potential on the membrane surface.The RO stage for reclaimed water mainly intercepted substances like humic substances and proteins,while the RO stage for salt concentration showed a poor rejection of tryptophan and SMP.Si and organic matters were identified as the main challenges in the ZLD process.Therefore,it is crucial to enhance the removal of DOM and Si at the pretreatment stage,to optimize the use of chemicals,and strengthen DOM and microorganism control in the whole system.These strategies are keys to improve the operational stability and membrane fouling mitigation.