Study On The Organic Wastewater Treatment With Packed Bed Three-dimensional Electrode Reactor

At present,the shortage of water resource in our country is a serious problem.Thus the research on efficient ways to improve the treatment and reuse of waste water is urgent.Three-dimensional reactor has been paid more attention to its application in the degradation of persistent organic pollutant,due to clean processing way,wide adaptability and high power efficiency.In this paper,the three-dimensional electrode reactor filled with activated carbon was used to degrade the organic substances.The different factors which had great effect on the degradation of organics were investigated.Then the mathematical model of semi-batch three-dimensional electrode reactor was established.Finally,the stability of particle electrode in the three-dimensional electrode reactor was studied,and the degradation pathways and mechanism of phenol in the three-dimensional electrode reactor were discussed.Firstly,the factors such as the current density,the electrolyte concentration,the initial pH value,the flow rate of organic and the initial organic concentration were examined to know about the pollutant degradation in the three-dimensional electrode reactor.The substances with different structures were degraded in the three-dimensional electrode reactor in order to illustrate the influence of molecular structure.The results showed that the phenol could be greatly removed about 98%at Q=65 mL/min,I=0.8 A,pH=3,C_phenol,0=0.2 g/L,C_{Na 2SO4}=1..2 g/L.For the rhodamine B degradation,the current density was the most obvious effect on removal efficiency.Secondly,the mathematical model of the semi-batch three-dimensional electrode reactor was established.According to the characteristics of the limiting current density in the packed bed three-dimensional electrode reactor,the reaction state was divided into three-stage processes:current control process,two-process control process and diffusion control process.Based on the Faraday's law,the kinetic equations were obtained.From the kinetic equation,it was shown that the kinetics of the reaction were not simple pseudo first order reaction,which changed from the zero order to the first order.To verify the feasibility of the mathematic model,the phenol wastewater was degraded in the three-dimensional reactor under different conditions.It was shown that the calculated data were in good agreement with experimental data in most cases.However,when the initial pH or initial phenol concentration was too high,the differentia between the calculated data and experimental data was increased.The possible reason was that the product of phenol degradation was polymers under the conditions.The accumulation of polymers was against to the assumption of the model,so that the results were not great.Finally,the microscopic morphology and crystal structure of activated carbon were analyzed by SEM and the XRD.The results showed that the stability of activated carbon was good.However,if the changes of morphology caused by the production of polymer or the corrosion caused by anodic oxidation during the degradation,it is not conducive to the long-term use of particle electrode.The changes of phenol degradation products under different pH values were analyzed by HPLC.It was found that the pathways of phenol degradation under different pH values were different.Under acidic conditions,the benzoquinone was predominant product,and then further degraded to glycolic acid.While under alkaline conditions,it was easy to produce polymers.