The Research Of Bioremediation Of Perchlorate-contaminated Groundwater

Perchlorate is a new type of persistent pollutant, soluble in water, stable and it hasa long half-life in environment for up to several decades. Nowardays, Perchlorate hasbeen reported to cause environmental problems in several parts of the world (globalpollutant). Perchlorate can penetrate into the organism of living beings throughdigestive and respiratory systems causing toxic effects to thyroid, growth, nervousand reproductive systems. Recently, several techniques (adsorption, Electrochemical,biological, etc) for removal of perchlorate from soil and water have been reported.Biological removal has been widely applied technology because of its high removalefficiency, low cost, and there is no secondary pollution.In this study, a group of bacteria capable to degrade perchlorate was screenedfrom the sediment of a river in Changchun. After PCR amplification and DGGseparation, the V3region was sequenced for DNA identification. The results ofsequence demonstration showed that the bacteria Citrobacter sp can degradateperchlorate. The best degradation effect was found at pH ranging7～8and bacteriainoculation amount is2%when sodium acetate was used as carbon source. When DOwas greater than5.18mg/L, the removal of perchlorate was inhibited. When thenitrate concentration was greater than100mg/L, it was found that Perchloratedegradative removal amount reduced with the increasing of nitrateconcentration.Moreover, it was found sulphate did not have effect to degradation ofPerchlorate. When the initial concentration of perchlorate ranged100-1000mg/L, itshalf-life was5～30h, and the zero order reaction was found to be the most suitable todescribe degradation kinetic.Soya-bean milk is a new approach of carbon sourcewhich have been used as a source of nutrients for bacterial growth. When soya-beanmilk was used separately as a unique source of nutrient was found that the amount ofperchlorate removal was high and soybean milk gradually released nutrients tosolution. Moreover, after reuse of soybean grain for18times the percolate degradative removal still reached75.44%.Four laboratory columns (A, B, C and D) were filled up with sand and activatedcarbon to simulated flow of ground water contaminated by perchlorate. Therefore, A,B and D were filled up with sand (without activation carbon) while the C column wasfilled with activated carbon at the middle part (reaction layer) and sand at the bothbottom and top. Then, soybean milk was used as nutrient for the column A, culturemedia(carbonsources、nitrogen source、microelement etc) for the columns B and C,and column D was the blank (without the addition of bacteria and nutrients). Theperchlorate amount in Column B was better than in column C which was ascribed toadsorption of both perchlorate and flora by activated carbon in column C.In thecolumn A was found a complete removal of perchlorate, moreover, the results was themost stable. The injection flow of15mL into the column can last for40daysremediating ground water contaminated by perchlorate pollutant. Therefore,soybeanmilk gradually released nutrients to ground water.