Effects Of Alternating Current(AC) Field And Organic Materials On Improving The Efficiency Of Sedum Alfredii Hance To Remediate Heavy Metal Contaminated Soil

The problem of soil heavy metal pollution becomes more and more serious. Using hyperaccumulator repairing heavy metal contaminated soil has become one of the hotspots of contaminated soil remediation. However, due to the influence of environmental factors, the efficiency of simply using phytoremediation tends to be low, and therefore strengthening measures are required, such as adding electric field, organic fertilizers and metal chelating agents, to improve the efficiency of phytoremediation. In this paper, pot experiments were conducted to investigate the efficiency of Sedum alfredii Hance repairing heavy metal contaminated soil by adding organic fertilizers and alternating current(AC) electric field. The main results were as follows:(1) Three kinds of organic materials i.e., biogas residue(BR), mushroom residue(MR), bamboo shell(BS) had consistent influence trends on pH of two soils(collected from Wenzhou and Fuyang, which referred to “Wenzhou soil” and “Fuyang soilⅠ”, respectively). Adding 5% MR significantly improved the soil p H. Soil organic matter contents were significantly higher by addition 5% organic materials than that of 1%. For soil available heavy metals, they were inhibited by 5% MR. In Wenzhou soil, 5% BR showed greatest activation to copper(Cu), zinc(Zn) and in Fuyang soilⅠ, BS and 1% MR had a certain improvement on the effectiveness of Cu, Zn, lead(Pb) and cadmium(Cd). For heavy metal accumulation in Sedum alfredii Hance shoots, at the first harvest, 5% BR and 5% BS had a better treatment effect; while at second harvest, three kinds of organic materials significantly increased heavy metal accumulation of Sedum alfredii Hance, and the remediation efficacy of 5% organic materials was better than 1% organic materials.(2) Under the alternating current(AC) electric field, the treatment effect of the voltage gradient of 0.5V/cm was greatest to increase the soil heavy metal availability while without plants. And with the power-on time increasing, under the voltage gradient of 1.0V/cm condition, heavy metal content of available had a certain growth trend. Grown with Sedum alfredii Hance, AC field showed small effect to enhance soil heavy metal availability: in the rhizosphere soil(0-10cm), energized 40 days, its influence was only observed by 0.5V/cm, and in non-rhizosphere soil(10-20cm), after adding organic material OM(5% BR), the heavy metal availability of two soils was significantly inhibited.(3) Energized 20 days with 0.5V/cm AC field significantly increased heavy metal concentrations in Sedum alfredii Hance shoots. With the extension of the power-on time(40 days), the effect of AC field on increasing Sedum alfredii Hance heavy metal concentrations significantly reduced. However, the addition of organic materials significantly reduced the heavy metal concentrations of Sedum alfredii Hance shoots.(4) The effect of AC field and organic materials on metal uptake by Sedum alfredii Hance varied with soil properties. In a soil mixed of “Wenzhou soil” and “Fuyang soilⅠ”, AC field effectively promoted heavy metal uptake by Sedum alfredii Hance, the effect of 0.5V/cm was superior to 1.0V/cm, while adding organic materials offset the AC field’s role. In Fuyang soilⅡ, AC field condition had no significant effect on heavy metal uptake by Sedum alfredii Hance.