Mechanism Of Cadmium Accumulation In Chlamydomonas Reinhardtii And Its Application In Wastewater Treatment

A rare metal element cadmium with toughness,ductility and corrosion resistance is released into the environment in large quantities by industrial production,which led to a serious cadmium pollution.Traditional wastewater treatment methods include chemical precipitation,electrochemical methods,membrane filtration,ion-exchange.These methods have high cost.Compared with these methods,biosorption has attracted extensive attention because of its advantages of economy,effectiveness and no secondary pollution.There are many kinds of organisms with the ability to absorb heavy metals,such as plants,fungi,bacteria and microalgae,among which microalgae have many species,wide distribution,strong adaptability,cheap and easy to obtain,and high adsorption capacity for heavy metals..However,there are two problems in the treatment of wastewater containing cadmium.First,microalgae in nature have poor tolerance to heavy metals,and heavy metals tend to inhibit the growth of algae.Second,the current technology of collecting algae is centrifugal collection,which consumes a lot of energy.In this study,the model organism Chlamydomonas reinhardtii was used as the research object to study the mechanism of cadmium enrichment,the preparation of cadmium resistant mutants through electric transformation and the application of cadmium resistant mutants to the treatment of cadmium containing wastewater.The main research contents and results are as follows:（1）The physiological effects of different concentrations of cadmium on C.reinhardtii and the submicrostructure of C.reinhardtii under cadmium stress were studied.Cadmium can reduce the growth rate of C.reinhardtii,affect photosynthesis,change the morphology of cells,and make cells accumulate organelles such as acidocalcisomes,plastoglobules,and starch granules.（2）FSD::Aph Ⅶ::RSD was randomly inserted into the genome of C.reinhardtii by means of forward genetics.After screening and identification with 500μM and 200μM cadmium chloride,we discovered one cadmium resistant mutant.（3）C.reinhardtii was immobilized in the embedding material of sodium alginate beads with additive of biochar and diatomite,this biochar-diatomite-alginate-jointly immobilized C.reinhardtii was used to remove cadmium from water.In the treatment of250μM of cadmium containing wastewater.The optimum conditions for preparation of the beads were as follows:sodium alginate mass fraction of 2%,diatomite mass fraction of 1%,biochar mass fraction of 0.1%and CaCl₂ concentration of 0.1 mol/L,and cadmium removal rate of beads could reach 63.41%.In summary,the physiological changes of chlamydomonas and the preparation of cadmium resistant mutants through electric transformation under cadmium stress provide a theoretical basis for the improvement of cadmium enrichment ability by genetic modification.Our research on the application of immobilization is helpful to improve the current situation of cadmium pollution in China by using microalgae.