Effect Of Micro-phyto Combined Remediation Of The Chromium Polluted Soil

Micro-phyto combined remediation change the existing forms of heavy metals and remove them from soil through metabolism, adsorption and transformation of microbe combined with enrichment and extract of plants. This technology has been recognized as a new-type bioremediation technology with advantages as simple operation, low cost and no second pollution.This paper takes the chromium polluted soil around a chromium slag yard in Henan Province as the research object to investigate the chromium pollution statue and thus confirm the remediation goals. On this basis, we studied the optimum addition ratio of chromium VI transforming agent prior to the enrichment effects of native selected plant. In this way, we explore a new method to repair the chromium polluted soil, which may be the technical reserve for future remediation of the chromium polluted sites. The main conclusions are as follows:(1) Investigation of chromium pollution statue showed the maximum and average content of chromium VI was 835 mg/kg and114 mg/kg, the maximum and average content of total chromium was 4410 mg/kg and 1109 mg/kg. Combined related standards of soil environment quality with the earlier risk assessment conclusions, the soil remediation goals of less than 50mg/kg for chromium VI and 300mg/kg for total chromium were confirmed.(2) First, the straw, BYM bacterium and excess sludge were used to transform the chromium VI. The single material tests indicated that all the three materials showed a certain transformation effect. Two materials mixing tests indicated that BYM bacterium effectively promoted the transformation of the straw and the excess sludge, and the transformation ratio increased 3 times and 25%, respectively. In three materials mixing test, the maximum of 95% chromium VI transformation ratio was observed with addition of a small amount of BYM bacterium in mixing materials of straw and excess sludge, which was 10% higher than that without BYM bacterium. the remediation goal of chromium VI was reached with the residual chromium VI in soil was 40mg/kg. In consideration of saving materials, cutting excess sludge addition and pollution risk of heavy metals, the optimum addition ratio of 3 materials was determined as: the straw 1%, the excess sludge 30% and the BYM bacterium 1%.(3) Phytoremediation was used to further remove the total chromium in the chromium VI- transformed soil. First, we screened a chromium abundant plant, cyperus rotundus, in the area around the chromium slag yard. In the test field of cyperus rotundus, the total chromium content decreased from 1000 mg/kg to 473mg/kg after 150 d, which was similar with that of the popular chromium abundant plant—festuca arundinacea, and the enrichment factor of cyperus rotundus was even more than that of festuca arundinacea. Furthermore, the biological activity of the repaired soil significantly improved with the increase of five orders of magnitude in colony-forming units.