Study On The Efficient Pretreatment Scheme Of Ethylene Waste Alkaline Oxidation Wastewater

Ethylene spent caustic is a kind of common alkaline pollution waste water in petrochemical industry.There are many kinds and high contents of pollutants in the waste water,and it must go through a certain pretreatment process before biochemical treatment.At present,wet oxidation process is widely used to treat ethylene spent caustic in China,but in practical application,there are many reasons such as equipment aging,pipeline corrosion and scaling,or changes in crude oil composition lead to unqualified effluent water quality of ethylene waste alkali oxidation unit.These waste water directly into the biochemical unit treatment will have a greater impact on the stability of the system.This paper focuses on the high-salt waste water discharged from ethylene waste alkali oxidation unit in a western refinery.The waste water has high conductivity and high concentration of sulfides and organic compounds,difficult to biodegrade.Through the experimental design an efficient pretreatment process to treat this unit of waste water,so that the treated water quality can reach the inlet index of the biochemical unit.This experiment mainly using electrodialysis technology for the high-salt waste water concentration and desalination processing.The sewage needs to be pretreated before the electrodialysis device.We compared the activated carbon filter and flocculation sedimentation,and the effects of two kinds of process of raw water treatment,Choose flocculation sedimentation technology as the process route of preprocessing scheme.In addition,in order to screen out the best flocculant combination,the flocculant and coagulant aid used in flocculation experiment were compared in depth.In the experiment of electrodialysis,we choose the best operating parameters to reduce the electrical conductivity of desalted fresh water below 4000 ?S/cm and the desalted fresh water recovery rate is above 60% after electrodialysis treatment.The quality of waste water treated by electrodialysis was analyzed and we decided to use freezing crystallization for the strong brine processing after electrodialysis.Inorder to achieve the goal of zero discharge of sewage.In view of the shortcomings of the biodegradability of desalted fresh water after electrodialysis treatment,we adopt the advanced oxidation technologies of ozone to improve their biodegradability.The final COD of sewage after treatment was stabilized below 250 mg/L,and the B/C value reached about 0.52.The effluent water quality meets the inlet water standard of the company's saline sewage treatment system.