Experimental Study Of Cadmium Removal By Chlorella Pyrenoidosa Biofilm

Cadmium pollution has become a serious environmental problem in our country.In this paper,Chlorella pyrenoidosa was selected,make its adherent growth in three-dimensional elastic carrier surface,until the algae biofilm formation.In this paper,the effects of heavy metal cadmium on the physiological activity of algal biofilm were investigated,then explored the initial concentration of cadmium,algal inoculation liquid ratio,light cycle,the initial pH for the removal of cadmium by microalgae biofilm.Determined the best combination level with the orthogonal experiments,then chosen the first three factors to conduct response surface experiments and established the response surface model for predicting the best condition and the best date of cadmium removal by microalgae biofilm.Under the condition of cadmium removal,studied the adsorption dynamics model and finally analyzed the microalgae biofilm functional group change by FTIR.The main conclusions of this paper as follows:(1)The physiological activity of algal biofilm will be affected by cadmium,which is.mainly reflected in the following five aspects:? In terms of the growth of biomass of algal biofilms,the low concentration of cadmium(? 2.5 mg/L)inhibited the growth of algal membrane biomass early,and then the biomass of algal biofilms began to recover;When cadmium concentration was high(? 5 mg/L),the inhibitory effect of cadmium on biomass growth of algal biofilms was significantly enhanced.? In the protein activity,the role of cadmium on microalgae biofilm can be divided into two phases:phase one,different concentrations of cadmium may stimulate the activity of protein and the protein content increased by cadmium stimulation;phase two,different concentrations of cadmium made the protein content decreased and the higher the cadmium concentration was the greater the decrease.? In the secretion of extracellular polysaccharide(EPS):when the cadmium concentration ?2.5 mg/L,the microalgae biofilm need about 4 days to adapt to the influence of cadmium and the content of EPS decreased in the,after the adaptation period the EPS production picks up and more than the normal state;When the cadmium concentration ? 5 mg/L,cadmium seriously inhibit the secretion of EPS and the contents has barely risen.?In the content of nitrate reductase(NR):In the low cadmium concentration group,the content of NR was increased,when cadmium concentration is 0.5 mg/L,1.0 mg/L,1.5 mg/L,the content of NR was increased more;In the high concentration group,the content of NR increased for the first five days,then the Cadmium began to inhibit the growth of NR.?From the perspective of the removal of cadmium,although microalgae biofilm affected by cadmium,but still retain the ability of removing cadmium.The removal rate is higher with the low concentration group of cadmium and the rate of removal can reach more than 90%;In the high concentration group,although the rate of removal not as good as low concentration group,but the remove quantity is more,when the cadmium concentrations is 15 mg/L,the highest removal rate is 89.93%.(2)The cadmium efficiency of algal biofilm was affected by the initial concentration of cadmium,inoculation of algal fluid ratio,light cycle,initial pH.? the highest cadmium removal rate is 89.93%,when the cadmium concentrations is 15 mg/L;? The highest removal rate of cadmium when the inoculation of algal fluid ratio is 1:2,and the highest removal rate is 92.4%.? The highest removal rate of cadmium when light cycle 10:14,and the highest removal rate is 91.6%.? The highest removal rate of cadmium when the initial pH is 8.0,and the highest removal rate is 91.9%.(3)The orthogonal experimental results shows that,the appropriate initial cadmium concentration,inoculation of algal liquid ratio,light cycle and the initial pH were beneficial to the growth of algal biofilm biomass and the removal of cadmium.The ability of cadmium removal as the main factor,the influence of various factors on the microalgae biofilm is B(initial cadmium concentration)>A(initial pH)>C(light cycle)>D(algal liquid ratio),and the highest removal rate of cadmium combination level is A2B2C1D1,namely the initial concentration of cadmium is 12 mg/L,the initial pH is 8.0,light cycle is 10:14,algal inoculation fluid is 1:4.(4)Response surface experiment results demonstrated that the initial pH and initial concentration of cadmium affected significant and predicted that the best condition of cadmium removal by Chlorella pyrenoidosa biofilm:initial pH is 8.00,light cycle is 11:10,the initial concentration of cadmium was 11.68 mg/L and finally the best removal rate prediction is 92.89%.(5)The dynamic experiment found that the cadmium removal is given priority to with adsorption and the removal of cadmium can be roughly divided into four stages,the first stage microalgae biofilm rapid absorption of cadmium ion by physical adsorption;In the second stage,the active adsorption capacity of algal biofilm is effective;In the third stage,the adsorption capacity of algal biofilm was saturated;In the fourth stage,a small amount of the cadmium ions which are not close to the physical adsorption released back into the environment.The adsorption kinetics model is more consistent with pseudo second order kinetics model.(6)Form the FTIR analysis of microalgae biofilm functional groups shows that the polysaccharide,protein,amino acid,hydrocarbon,lipid and fatty acid compounds in the biofilm are changed in the adsorption process change.