Study On Simultaneous Removal And Concentration Of Nitrogen And Phosphorus In Sludge Hydrolysis Acidification Solution By Electrodeionization Technology

Sludge hydrolyzation acidification solution which contains a large number of volatile fatty acids?VFAs?often used as denitrification carbon source in wastewater treatment plants.The presence of nitrogen and phosphorus in the acidification solution aggravates the load of nitrogen and phosphorus removal in the wastewater treatment plant.Removal of this part of nitrogen and phosphorus is of great significance.With the rapid development of modern industry,a large number of nitrogen and phosphorus elements enter the natural water,resulting in eutrophication,seriously damaging the aquatic ecological environment.How to effectively remove nitrogen and phosphorus is the focus of research in the current removal technology at this stage,and the recovery of them be neglected.In recent years,the shortage of nitrogen and phosphorus resources has become increasingly severe.Therefore,it is imperative to seek a technology that can simultaneously remove and recover nitrogen and phosphorus nutrients.Electrodeionization technology?EDI?combines ion exchange and electrodialysis organically to achieve the deep removal and concentration of ions simultaneously under the direct current electric field.At present,there have been numerous studies on ultrapure water production and the removal and recovery of heavy metal ions,and few researchers study on the treatment of nitrogen and phosphorus.In this paper,EDI technology was used to treat nitrogen-phosphorus mixed solution.A systematic study was made on both the cyclic and continuous influent modes.Furthermore,the rules were explained and the mechanism was analyzed.An EDI reactor which is independently designed and produced was used in this study,and the effect of operating conditions on the removal of nitrogen and phosphorus was explored through a single-factor expeiment in the cycle operating mode.The study found that use of sodium sulfate as electrode solution can increase the removal efficiency of nitrogen and phosphorus nutrients.When the concentration of sodium sulfate is 0.05 g/L,and the proportion of the anion and cation exchange resin?D201 and D001?is 1:1,the removal rate of nitrogen and phosphorus reaches the highest.Increasing the voltage can improve the removal rate of nitrogen and phosphorus,but the excessively high voltage will accelerate the hydrolysis and resin desorption of the membrane stack,then reducing the quality of the effluent water.Increasing the water flow means shorten the residence time of ions in the dilute chamber and reduces EDI processing performance.Further research is needed to explore treatment ability of nitrogen and phosphorus removal and concentration in the continuous operating mode.The results showed that when the voltage is 30 V,the water flow of dilute chamber is 1mL/min,the NH₄⁺and PO₄^3-removal rates were up to 79.94%and 81.62%,respectively,and the concentration factor were 2.94 and 2.30 after 8 h of continuous operation At this time,the current efficiency reached 57.69%,indicating that the EDI reactor can remove and concentrate nitrogen and phosphorus nutrients at the same time..It was found that increasing the voltage can reduce the current efficiency of the EDI system,and the proportion of the current used to transfer the Ni4+ and the PO₄^3-is relatively reduced.Therefore,although increasing the voltage can improve the water quality,it also increases the energy consumption So appropriate voltage should be selected according to the demand.Water flow has a great influence on the performance of EDI on the removal of ions,and increasing the water flow rate will result in a significant decrease in the water quality of the effluent.In addition,increasing the voltage can increase the average migration rate of ions,but increasing the water flow has no significant effect on the average migration rate of ions.When the voltage is 30 V,the water flow is 1 mL/min,and the average migration rates of NH₄⁺and PO₄^3-are 4.32 mg/h and 2.44 mg/h,respectively,indicating that the closer ion average migration rate is with the input rate,the better water quality is.The energy consumption results showed that the energy consumption of concentrated nitrogen and phosphorus nutrients are 1.98 kWh/mol and 20.53 kWh/mol,respectivelyIn summary,with the continuous operating mode,simultaneous removal and concentration of nitrogen and phosphorus can be achieved under optimized conditions.This study provides theoretical basis and experimental data for the further application of EDI technology in the treatment of actual hydrolytic acidification solutions.