Studies On The Removal Mechanism Of Hexavalent Chromium And O-nitrophenol By Chlamydomonas Reinhardtii

Heavy metals and synthetic organics pollution are important environmental problems.The simultaneous removal of heavy metals and synthetic organics is a technical problem we are facing.Microalgae have been widely used for the removal of heavy metals or synthetic organics;however,the simultaneous removal of them is rarely studied.In this study,a green algae,Chlamydomonas reinhardtii,was used to simultaneously remove hexavalent chromium（Cr（VI））and o-nitrophenol（ONP）.The effects of Cr（VI）and ONP on the photosynthetic system,antioxidant system,soluble protein contents and cell morphology of C.reinhardtii were studied.In addition,the mechanisms of removing Cr（VI）and ONP were discussed.The main results are as follows:（1）The removal effect and mechanism of C.reinhardtii on Cr（VI）or ONP were studied.The highest removal rates of Cr（VI）and ONP were 39.25%and 38.92%,respectively.It was also found that C.reinhardtii contained Cr（VI）-reductase and ONP-degrading enzyme,and the possible pathway of ONP degradation by C.reinhardtii was speculated.ONP was first degraded to nitrobenzene,phloroglucinol,catechol and phenol.2-Nitropropane was produced by the removal of benzene ring from nitrobenzene,and NO₂ was finally transformed into NH₄⁺.Phloroglucinol,pyrocatechol and phenol split to acetaldehyde,hexanol and 2-butene-1,4-diol.Acetaldehyde was then oxidized to acetic acid,which reacted with ketene and ethanol to form acetic anhydride and ethyl acetate,respectively.Hexanol was oxidized to 2-hexanal,and then split to butenal.2-Butene-1,4-diol was oxidized to maleic acid.（2）The toxic effects of Cr（VI）or ONP on C.reinhardtii were studied.Cr（VI）and ONP both inhibited the photosynthesis of C.reinhardtii,increased the contents of reactive oxygen species（ROS）and malondialdehyde（MDA）,and decreased the activity of superoxide dismutase（SOD）and the contents of soluble protein.They also changed the surface characteristics and shape of C.reinhardtii,however,the lower concentration of ONP promoted the physiological activity of C.reinhardtii.Moreover,the combined toxic effects of Cr（VI）and ONP on C.reinhardtii were antagonistic inhibition.（3）The combined removal effect of C.reinhardtii on Cr（VI）and ONP was studied.Under the combined treatment,the removal rate of Cr（VI）and ONP increased to 54.92%and 45.92%,respectively.ONP promoted the removal of Cr（VI）by increasing the contents of Cr（VI）-reductase in C.reinhardtii and decreasing the p H value of the culture medium.Cr（VI）promoted the degradation of ONP by stimulating C.reinhardtii to produce ROS.