Study On The Resource Utilization Of Nanofiltration Concentrate In Zero Discharge System Of Desulfurization Wastewater

The release of the Action Plan for《Water Pollution Prevention and Control》and《the Guide to Possible Technologies for Pollution Prevention and Control in Thermal Power Plants》marked the higher requirements for environmental protection,so it is imperative to achieve zero discharge of desulfurization wastewater.At present,the zero discharge treatment technology of desulfurization wastewater from coal-fired power plants mainly includes pretreatment technology,concentration and reduction technology,evaporation and crystallization technology and so on.A power plant in Zhuozhou adopts"pre-sedimentation tank+secondary coagulation clarification sof-tening+ultrafiltration+weak acid ion exchange+nanofiltration+reverse osmosis+evaporation crystallization"treatment process to deeply treat desulfurization wastewater and realize zero discharge of wastewater in the whole plant.A new prob-lem ensued is that how to treat new end-of-pipe wastewater—nanofiltration concen-trate.At present,the common treatment method is to return the concentrated water to the conditioning tank,which has the disadvantage of depleting the membrane treat-ment system and greatly increasing the operation cost.Based on the water quality and quantity analysis of nanofiltration concentrate,this study proposes to combine the nanofiltration concentrate solidification treatment technology with the non-burning brick process,and use nanofiltration concentrate instead of process water for non-burning brick producting,so as to realize the resource utilization of nanofiltration concentrate.According to the existing non-burning brick technology,non-burning fly ash brick technology,non-burning slag brick technology and foam concrete solidified technology are proposed.Firstly,orthogonal experiments are designed to evaluate the water absorption,compressive strength and water-soluble chloride ion content of the solidified body,and the effects of water-cement ratio,cement admixture and lime ad-mixture on the water absorption,compressive strength and water-soluble chloride ion content of the solidified body are analyzed,and the best ratio is given with the char-acterization analysis.The advantages of water reducing agent application are then de-termined by designing admixture application experiments,and sodium lignosulfonate is selected for using as an admixture in future experiments.Next,the non-burning slag brick experiments are designed with the slag ratio as the independent variable to de-termine the optimal slag mixing ratio,and then the slag-free brick curing formula was further optimized by adjusting the water reducer addition.In order to explore the best mean of solidified nanofiltration concentrate,foam concrete curing experiment is fur-ther designed.Finally,the possible effects of high Na⁺and SO₄^2-content in nanofiltra-tion concentrated are investigated with the existing process profile of a power plant in Zhuozhou.The paper finally proposes a process route based on the application of nanofiltra-tion concentrate to the preparation of non-burning bricks,and conducts a tech-no-economic assessment,which not only solves the problem of the outlet of wastewater at the end of the power plant,but also reduces the cost of consuming pro-cess water in the power plant by"turning trash into treasure",which is in line with the circular economy development model.