The Performance Study And Process Optimization Of Ammonia Removal By Flow-electrode Capacitive Deionization

The resource utilization of nitrogen in wastewater shows significance for environmental sustainable development.As its representative process,the combination of conventional activated sludge process and Haber-Bosch process is commonly used today.However,due to the long nitrogen cycle chain,it usually faces the problems of high energy consumption and low recovery rate in the process of resource utilization.Therefore,it is necessary to study a new high-efficiency and low-energy consumption nitrogen recovery process.Combination of flow electrode capacitive deionization（FCDI）and ammonia recovery processes such as hollow fiber membranes and flat breathable membranes.As a new type of nitrogen removal and recovery process,ammonia removal process has the advantages of high nitrogen removal and recovery efficiency and low energy consumption.In this paper,the FCDI process is used to remove NH₄⁺from wastewater,to concentrate in electrode solution,and hollow fiber membranes and flat breathable membranes are used for the purification and recovery of NH₄⁺.The influencing factors of the performance of NH₄⁺removal by FCDI are investigated,and models simulated processes including removing NH₄⁺by FCDI and reclaiming by membrane ammonia are constructed.Using the models,the mechanisms were clarified,charge transfer pathways were discussed,the device structure and operating parameters were optimized.Then scenario analysis of ammonia reclamation from various wastewater water inlet conditions were discussed.All the results provide reference and support for practical application.The main conclusions obtained are listed as follows:1.Research on the influencing factors of the ammonia removal by FCDI.From the perspective of ammonia removal capacity,the NH₄⁺removal efficiency increases with current density increasing,and decreases with the influent flow rate increasing.The maximum value is 98.2%when the influent flow rate is 0.7 m L/min.When the mass fraction of activated carbon in the electrode solution increases from 5%to 10%,the NH₄⁺removal efficiency increases,and when it exceeds 10%,it tends to be stable.From the perspective of energy consumption,the energy consumption required to remove unit mass of N decreases with the increase of the influent flow rate and the mass fraction of activated carbon in the electrode solution.While it increases with the increase of the current density.From the perspective of continuous operation of ammonia removal capacity,the average salt adsorption rate ASRR increases with the increase of the influent flow rate,current density,and the activated carbon mass fraction in the range of 5%to 10%.While it increases with the activated carbon in the range of greater than 10%,and tends to be flat.2.Construction and verification of ammonia removal models by FCDI process Based on electric double layer theory and ion transport theory,combined with potential balance and mass conservation,the electrochemical model for NH₄⁺removal by FCDI.The p H influence and multi-ion competitive adsorption was included in this model.The simulation accuracy of NH₄⁺removal efficiency experiment results reached 93.8%,the overall fitting effect is improved.3.Model construction,verification,comparison and selection of ammonia recovery processTaking the effluent of the FCDI model to remove NH₄⁺as the inlet water condition,based on the ionization balance,dissolution balance and mass transfer equation,the hollow fiber membrane and flat gas permeable membrane were used to establish the mass transfer model for ammonia recovery.The simulation accuracy of the recovery efficiency experiment results reached 76.7%and respectively 90%,the overall fit is good.The normalized recovery efficiency was used to compare and select the two processes,and finally the flat gas permeable membrane ammonia recovery process was selected for subsequent research,due to better performance.4.Optimization of FCDI and flat gas permeable membrane ammonia recovery hybrid processThe model established in this thesis was used to a simulation scenario of the influent of a municipal sewage plant,two indicators of ion selectivity and removal rate were calculated,and the mechanism of the influence of operating parameters on ammonia removal was qualitatively explained.The optimal combination of process parameters was analyzed to be the influent flow rate of 1.24 m L/min,the current density is 21.26 A/m²,the mass fraction of activated carbon is 10%,and the acid flow rate is50 m L/min,which has achieved ideal ammonia removal performance.The FCDI ammonia removal device was connected in series under the condition of keeping the length of the flow channel of the desalination chamber unchanged,the removal efficiency of the improved device increased by 31.8%,and the energy consumption per unit mass of N removal was reduced by 26.1%,which has achieved the target of optimization.Applying the model to a simulated situation of urine treatment,the optimal combination of process parameters is analyzed as follows:the influent flow rate is 0.64m L/min,the current density is 235 A/m²,the activated carbon mass fraction is 10%,and the acid flow rate is 50 m L/min,which has achieved ideal ammonia removal performance.The FCDI ammonia removal device was connected in series under the condition of keeping the length of the flow channel of the desalination chamber unchanged.The removal efficiency of the improved device increases by 9.3%,and the energy consumption for removing unit mass of N is reduced by 40.7%,which has achieved the target of optimization.The results of this paper show that NH₄⁺removal by FCDI and the ammonia recovery model can effectively realize the performance research and optimization of the FCDI ammonia removal process,and can provide reference support for the promotion and application of the process.