Chlorella’s Intoxification And Detoxification To Nickel Or Chromium In Water And Its Adsorption Removal Efficency

As a kind of widespread organism in water, is breeding fast and easy to large-scale farming, as well as having some capable of adsorption to heavy metals, which make it low cost in water treatment work using microalgae. However, the toxicity to algae living bodies of heavy metals affects the normal growth of algae, which inhibition of the applications of algae in water treatment. Algal cells can reduce the toxic effects of heavy metals through a series of physical activities under heavy metal stress, which has important practical significance for the application of active algae in the water of heavy metals. We can try some artificial means to change the living environment of chlorella, which is possible to make some low-cost water purification with the use of living Chlorella physiological activity.The toxicological studies are static experiments, with Chlorella, Scenedesmus algae, Microcystis aeruginosa that is commen in our water. Obtained the half inhibitory concentration of Ni（II） is 5.58 mg/L, 5.25 mg/L, 4.35 mg/L respectively. And the half inhibitory concentration of Cr（VI） is 4.85 mg/L,4.83 mg/L,4.73 mg/L respectively. Obtained the tolerance of three algae to Ni（II） and Cr（VI） by comparing the changes in concentration of Chlorophyll a, intracellular and extracellular protein soluble sugar of Chlorella and Scenedesmus obliquus under different heavy metal stress. The results showed that Chlorella has a better tolerance to heavy metals. Persistent toxicity studies indicate that Chlorella can’t be completely killed by heavy metals, and it can continue to proliferate in the case of environmental improvement.Experimented with different initial cell density, different initial concentrations of heavy metals, different p H, and different temperatures in the adsorption experiment,. The results showed that Chlorella has a good adsorption effectiveness to Ni（II） and has absorption and conversion performance to Cr（VI）. In several of the selected cell density, the experimental results were not significant. Further experiments showed that good adsorption and conversion to these heavy metals can be carried on in the range of heavy metals below 5 mg/L and acidic, and elevating temperature can improve the performance of adsorption and conversion. By infrared spectroscopy, in the process of adsorption and conversion, obtain the functional groups C-O, C=O, COOH,-NH- and other groups, which are the main role of the functional groups.In the experimental part of the detoxification mechanism, we analyzed the situation of heavy metal concentration 5 mg/L. Peroxide phenomena are described focusing on the content of superoxide radicals（?O₂^-） and hydrogen peroxide（H₂O₂）. And Carry out further explanation by the content of peroxidation product malondialdehyde（MDA）. During this process, ROS was adjusted by SOD and CAT, and its concentration ascended and then declined. And it was analyzed non-enzymatic detoxification pathways from the change of the GSH’s content and extracellular substances. As highly toxic substances, hexavalent chromium has been converted into low or non-toxic trivalent chromium and divalent chromium in this process. Finally, causes and mechanism of the conversion of hexavalent chromium were analyzed. Chlorella can reduct of hexavalent chromium by synthesis of the secondary alcohol group, as well as the chloroplast by electron transferring.