Experimental Research On The Electrochemical Remediation Of Fluoranthene Contaminated Soil

Polycyclic aromatic hydrocarbons(PAHs) are a group of persistent organic pollutants which are widely distributed in the environment. Most of them are highly carcinogenic, mutagenic, teratogenic and also refractory, bioaccumulative substances. It has been attracted extensive attention of experts and scholars in China and abroad. As an important carrier of PAHs, more than 90% of the PAHs finally absorbed onto the soil/sediment. And a growing number of studies show that PAHs contaminated soil has became a threat to the environment and human health. According to a survey, the composition of PAHs in surface soil of main areas in China, the relative content of fluoranthene was 16.22% of the total PAHs, rank the second after Phenanthrene. So, choosing fluoranthene as the target polltants was significant. PAHs contaminated soil can be treated by in situ and ex situ methods. In situ remediation has the disadvantages of high cost, digging of the soil and increasing of process, can not be applied on a large scale. While in situ remediation has a marked characteristic of low cost. In situ bioremediation technology can effectively remove PAHs with small molecular weight, for the degradation of high molecular weight is less effective. The PAHs soil decontamination by means of the electrochemical remediation is still in an initial stage, but many researchers have demonstrated the treatment effectiveness. And it has a promising prospect of application.This experiment mainly studyed on the optimization of extracting fluoranthene from the tested soil, adsorption and desorption properties of fluoranthene on soil. Investigated the influence on the removal efficiency of fluoranthene in the soil with different voltage and space between electrodes and different kind of electrode materials. Compared the degradation effect of fluoranthene by using the integrated technologys of electrochemical remediation with Surfactant alpha alkenyl sodium sulfonate(AOS), Electro-Fenton method and Induction-Electro-Fenton method. The main results are listed as following:(1) Using methanol as extractant, 30 min of ultrasonic extraction followed by 30 min of oscillation under 25?, the average extraction rate of fluoranthene in the artificially contaminated soil is 86.39%. Fluoranthene adsorption on to soil can be well simulated by Linear adsorption isotherm model and also Freundlich isotherm model, the correlation coefficient was 0.9663 and 0.9859 respectively. The desorption of fluoranthene in the contaminated soil can be affected by the concentration of AOS, when the concentration is below the critical micelle concentration(CMC), it can barely help to the desorption, while increasing the concentration to 4 times of CMC, the elution ratio of fluoranthene in the soil can go up to 26.56%(2) Keep the electrodes space constant and increase the voltage between the electrodes can help to improve the removal efficiency of fluoranthene in the contaminated soil. When raising the voltage from 5 V to 50 V, with 15 days of reaction, the average removal efficiency of fluoranthene in the soil increased from 19.87% to 32.84%. Meanwhile, The increase of voltage significantly affected the soil pH and electrical conductivity, In the No.1 and No. 5 sampling point, the pH were 2.64, 10.82, the conductivity values were 1041, 335 ?S/cm respectively when the voltage between the electrodes was 50 V.(3) Maintain the the voltage between the electrodes and decrease the distance between the electrodes can also improve the removal efficiency of fluoranthene. When the spacing of electrodes change from 25 cm to 10 cm, the average removal efficiency of fluoranthene in the soil increased from 29.04 % to 39.95 %. No matter keeping the distance of electrodes constant, change the voltage or maintaining the voltage, narrow the spacing, actually both were increasing voltage gradient and can improve the removal efficiency of fluoranthene. At the same time, it will aggravate the occurrence of adverse reaction of electrolysis of water, thus affecting the soil pH and electrical conductivity.(4) When using graphite and Q235 steel plate as electrodes during the electrochemical remediation process, the average fluoranthene removal efficiency were almost the same, for 32.84%, 33.78% respectively. However, under the condition of the iron electrode, the removal efficiency among the sampling points were more different than that of the graphite electrode.(5) Adding low concentration of AOS solution can barely help to enhance the removal efficiency of fluoranthene in the contaminated soil during the electrochemical remediation. The removal efficiency of some sampling points were even inhibited when the AOS concentration was 0.5 times of CMC. While high level of AOS solution can promote the removal efficiency of fluoranthene, when the AOS concentration is 4 times of CMC, the average fluoranthene removal rate improved from 29.04% to 39.13% compared to without adding AOS.(6) Using iron electrodes together with hydrogen peroxide to induce Electro-Fenton reaction can effectively improve the removal efficiency of fluoranthene in the soil, and the average removal efficiency was 50.81%. While individually using iron electrode or hydrogen peroxide, the average removal efficiency of fluoranthene were 33.78% and 32.56% respectively.(7) The pH change regularity of sampling points are different from the conventional electrochemical remediation when using Induction-Electro-Fenton method. The pH value of all the sampling points were in the range of 5~8. And the the removal efficiency of fluoranthene in the contaminated soil was 46.56%. After adding AOS solution with the concentration of 4 times of CMC into the Induction-Electro-Fenton, the the removal efficiency increased from 46.56% to 54.28%, while the pH showed a similar tendency with the Induction-Electro-Fenton, but the value of pH was slightly lower than solely using Induction-Electro-Fenton method.