Removal And Recovery Of Phosphorus From Low-strength Wastewaters By Flow-electrode Capacitive Deionization

When the content of phosphorus(P)in natural water exceeds a certain level,it will lead to eutrophication and affect the quality of water.Phosphorus is an important nutrient element necessary for human beings,animals and plants to maintain the basic functions of biology.At the same time,phosphorus is a non-renewable resource,and its existence in nature is very limited.The exploitation and loss of phosphate ore has caused a serious shortage of phosphate ore resources in the world.It is reported that if the demand for phosphorus increases by 3% a year,the world’s phosphorus stocks will be depleted in the next 100 to 400 years.Phosphorus recovery from wastewater is not only beneficial to alleviate the phosphorus crisis,but also helpful to reduce water pollution and phosphorus removal load,which is the inevitable requirement of sustainable development.So the study of phosphorus removal and recovery from wastewater has very important significance.In recent years,electrochemical process has been widely used in water pollution treatment,among which Flow-electrode Capacitive Deionization is a new technology with great advantages in water pollution treatment.In this study,the flow electrode capacitive deionization technology was used to remove and recover phosphorus from low concentration phosphorus containing wastewater,so as to realize the sustainable utilization of phosphorus.The effects of the applied voltage,the flow velocity and direction of the wastewater into the device,the initial phosphorus concentration in the wastewater,the content of carbon black in the flow electrode and the initial p H value of the wastewater on the phosphorus removal performance of FCDI were systematically studied.The results show that the applied voltage and the initial p H value of wastewater have great effects on the removal efficiency of phosphorus.With the increase of applied voltage,the phosphorus removal efficiency of FCDI device gradually increases.When the applied voltage increases from 0 V to 1.2 V,the phosphorus removal efficiency increases from 2.11% to 97%.Due to the different forms of phosphorus in water environments with different p H values,the removal efficiency of phosphorus from wastewater by FCDI device is also changed when the p H value of water is changed.When the p H value of wastewater is alkaline,the removal efficiency of phosphorus from wastewater by FCDI is poor.When the p H value of wastewater is 10,the removal efficiency of phosphorus is 58.18%.When p H value is 5,the removal efficiency of phosphorus is 97%.Through optimizing the process parameters,the optimal operating conditions were determined as follows: the applied voltage was 1.2V,the flow rate of wastewater was 10 m L/min,the content of carbon black in the mobile electrode was 1wt%,and the initial p H value of wastewater was 5.Under these conditions,the removal efficiency of phosphorus in wastewater reached 97%.After 6 consecutive cycle tests,the FCDI device showed good phosphorus removal performance,and the phosphorus removal efficiency was kept at about 97%.In addition,low-concentration phosphorus containing wastewater(100 mg P/ L)can be effectively concentrated 16 times.After 11 h of concentration experiment,the final concentration of phosphorus in the effluent is16.8 mg P/ L,and the content of phosphorus in the mobile electrode is 1567 mg P/ L,the volume of waste water is reduced by 20 times.The above results show that the FCDI system has a good performance for phosphorus removal and concentration.