Sequentially Removal Of Cd (Ⅱ) By Natural Adsorbent Rape Stalk And Heavy Metal-resistant Endophytic Bacteria Arthrobacter Sp. LKR02

With the development of industry, such as battery manufacturing,mining, paint production, smelting and metal plating, and ammunitionproduction, heavy metal pollution becomes more and more serious.Cadmium （Cd） is known to be one of the most toxic heavy metals due to it sserious damage to bones and kidney as a result of accumulating in humansvia food chains. Recently, intense attention has been paid on bioremed iationwhich utilize plant waste material and microbe. The natural plant materialadsorbent and microbial biomass have arisen as economic and eco-friendlyoptions for heavy metal wastewater treatment. Regrettably, the unmodifiednatural adsorbents always cause high che mical oxygen demand （COD） andcolour after treatment due to the release of some organic matters fro madsorbents. Si milarly, the maintenance of microbial cells duringbioremediation process is restricted by heavy metal toxicity, extremes pH ofsolution and the de mand of additional nutrients. A novel method wasestablished to sequentially remove Cd²⁺from contaminated water bycombining natural plant material （1st phase） and endophytic bacteria （2ndphase）.In this study, natural adsorbent rape stalk was primarily used to removeCd²⁺from contaminated water. Subsequently, Cd-resistant endophyticbacteria Arthrobacter sp. LKR02was inoculated in the pretreated water t oassi milate organic compounds which stained by rape stalk and adsorbedresidual Cd²⁺. In the1st phase, with a series concentration of Cd²⁺fro m11.24to78.68mg/L the Cd removal efficiencies were ranged from81.53%to87.54%, and the maximu m adsorption capacity obtained was31.5mg/g（pH6.5and5g/L adsorbent dosage）. The Equilibrium adsorption datas weremore consistent with the Langmuir isotherm equation than the Freundlishisotherm equation. Pseudo-second-order kinetics fitted better to adsorptionprocess compared with pseudo-first-order kinetics and intra-particlediffusion model. The regene ration efficiency of rape stalk was still higherthan82.60%after4desorption/adsorption cycles. The SEM figures revealthere is nearly no significant difference between the surfaces of the two. In the2nd phase, thirteen endophytic bacterial strains isolated from theCd-hyperaccumulator Solanum nigrum L. were tested to screen the optimalone which not only metabolize the organic matters stained by rape stalk butalso adsorb the surplus heavy metal cadmium efficiently. Maxi mu mreduction in COD （97.57%）, and colour （91.93%） were obtained withLKR02after36h aerobic incubation. The total Cd removal efficiencieswere rising to96.31%and99.76%, respectively. The selected LKR02strains were identified by determination of16S rDNA gene sequence. On thebasis of biochemical characteristics, morphological, physiological andcomparative analysis of the sequence with already available database, itshowed that the LKR02was close to the member of the genus Arthrobacterand showed nearly100%homology with Arthrobacter oxydans. At theconcentration of44.96mg/L of Cadmium ions, the lag phase was extendedbut the maximal cell density was reduced only below29.65%as the control.LKR02has a relative stable and efficient capacity of Cd uptake fro mwastewater at pH6.0-8.0, and with a sharp decrease at pH9.0.In the presence of4.725,8.850,14.525mg/L of Cd2+, The Cd adsorbedon the cell wall and absorbed on intracellular cell through metabolicdiffusion were65.29%,67.43%,68.86%and34.71%,32.57%,31.14%,respectively. The LKR02isolated from the cadmium Cd-hyperaccumulator S.nigrum L showed a good resistance and excellent intracellular accumulationcapacity of heavy metal.Considering the advantages of natural adsorbent and microbe in heavymetal re mediation, we have established a novel method to remove Cd²⁺fro mcontaminated water step by step by using natural adsorbent for firstadsorbing most of heavy metal and endophytic bacter ia for further removingresidual heavy metal and reducing COD and colour. This method is moreeconomical, efficient and environment friendly than traditional methodswhich exclusive using plant adsorbents with chemical modification as wellas the microbe absorbents.