Optimization Of Cadmium Removal Using Response Surface Methodology By Microbial Flocculants And Investigation Of Flocculation Mechanism

A bacterial strain named Paenibacillus polymyxa GA1can produce bioflocculantwith high flocculating activity was screened from soil. Microbial flocculant GA1withirregular structure was composed of polysaccharide and protein, content ratio was68.64%68.64%, while weight percentage of C, N, O, elements was2.74%57.3%and2.74%respectively.In this study, microbial flocculant GA1（MBFGA1） was used to removalcadmium from wastewater. Cadmium removal from wastewater was investigatedusing central composite design （CCD） method, and flocculation mechanism wasanalyzed by fourier transform infrared （FTIR） spectra coupled with environmentalscanning electron micrograph （ESEM）. In CCD method, cadmium removal efficiencywas served as response value and initial concentration of Cd²⁺, MBFGA1dosingquantity, pH and reaction time were also optimized. Results from the analysis ofvariance demonstrated that the model was highly significant, in which the model Fvalue was11.71and P value was less than0.0001, and correlation coefficient was0.9154. Parameters of initial concentration of Cd²⁺, pH and reaction time wereextremely significant factors. According to the model, initial concentration of Cd²⁺and MBFGA1dosing quantity,Initial concentration of Cd²⁺and reaction time, as wellMBFGA1dosing quantity and reaction time were significant interaction term.Theoptimum values of the variables were found to be Cd²⁺initial concentration23.60mg/L, MBFGA1dosing quantity27.74mg/L, pH9.5and reaction time15.97min,respectively. Under the optimum conditions, it can reach99.5%of cadmium removalefficiency. FTIR spectra results indicated that carboxyl, hydroxyl and phosphategroups of the microbial flocculants participated in this flocculating process andmeanwhile the hydrogen bond was generated. In combined with the results of ESEM,MBFGA1molecules overlap each other in the process of flocculation, which makingmore molecules linked together. it can be inferred that MBFGA1has Strong waterpurification ability on removal havey metal icon in wastewater By back scattered electron imagings and energy dispersive spectrometer photos. All in all, it could beconsidered that chemical reaction, adsorption bridges, hydrogen bonding and VanderWaals force were all contributed to flocculation mechanism.