Experimental Study On The Degradation Of Dimethoate By Microorganisms And The Retention Of Cadmium Ions

Organophosphorus pollution and heavy metal pollution are two urgent environment issues in China,which have aroused public attention.In this article,organophosphorus pesticide dinethoate and Cd2+ were used to culture Chlorella vulgaris and Pseudomonas putida,in order to explore the microbial-degradation of organophosphorus pesticides,biomineralization and mineral holding function for Cd2+.In this study,C.vulgaris was cultured in modified M11 medium.Dimethoate and calcium chloride were used as the carbon source and calcium source respectively.After 12 days,the concentration of Ca2+ and dimethoate in culture as well as the mineral and chemical composition of sediment was detected by scanning electronic microscopy(SEM),X-ray diffractometer(XRD),performance liquid chromatography(HPLC),anatomic absorption spectrophotometer(AAS)and enzymatic determination.Results showed that,the biomass of C.vulgaris and the pH value of the nutrient solution had experienced rapid growth,while the concentration of Ca2+ in the culture solution decreased significantly.Large amounts of biogenic sedimentary CaCO3 and little calcium carbonate with magnesium were detected by SEM in the precipitates at the bottom of the bottle.Results indicated that,chlorella can degrade dimethoate and induce biological mineralization.Further study was carried out to study the mineral immobilizing function of the Ca3(PO4)2 and CaCO3 generated by C.vulgaris.Different concentration of Cd2+solutions were added in mediums separately at different time.AAS and enzymatic determination were used to measure the concentration of Cd2+.Besides,SEM was used to observe mineral and chemical composition of the sediments.Results showed that C.vulgaris could not grow in the mixed culture solution of 250 mg/L dimethoate and 1 mg/L Cd2+.However,if we culture C.vulgaris in the dimethoate medium and add Cd2+in the logarithmic phase,the biomass of C.vulgaris will increase.The removal rate can reached to 33.97%with the total removing amount of 0.890 mg/L.Besides calcium carbonate,Cd also was detected by SEM and EDS.C.vulgaris can not inoculated directly in the synthetic wastewater with dimethoate and Cd2+,which limits its application.Therefore,P.putida was selected as experiment strains to degrade organic phosphorous dimethoate and remove the heavy metals Cd2+.Results showed that,P.putida could grow well in this culture system.In two contrast tests,with 6mg/L and 15mg/L Cd2+,the removal rate both reached 100%.Furthermore,large amounts of biogenic sedimentary CaCO3 and little Ca3(PO4)2 were detected by SEM and EDS in the precipitates at the bottom of the bottle.This study provided a new way to treat wastewater polluted by organophosphorus pesticide and heavy metals.