| As the biosorption for heavy metal bioremediation in pollution water, microalgae have the advantages beyond physical and chemical methods, so it is one of the research focuses on heavy metal bioremediation in pollution water. In this paper, effects of Chlorella pyrenoidosa on heavy metal removal with single and combined pollution water were carried out, and we also explored the influence of single and combined heavy metal pollution on the growth characteristics and biochemical composition of algal cells. Finally, effects of common algal powder, wall-breaking algal powder and lipid extraction algal powder on heavy metal removal (copper, cadmium, lead) in single and combined pollution water were conducted in the present study. The main results are listed as following:(1) Copper, cadmium, lead solution with four kinds of high concentration gradient respectively were selected for the research on the effects of Chlorella pyrenoidosa on heavy metal removal within72h in singled pollution water, and the influence with the presence of single heavy metal on growth characteristics and biochemical composition of Chlorella pyrenoidosa were also carried out in the study. Results showed that the removal of copper, cadmium, lead by Chlorella pyrenoidosa within72h was a relatively rapid process, and the process of heavy metal removal can be significantly affected by different initial concentrations. For example, the removal rate reached85.0%at30min under the initial copper concentration of1mg·L-1, and the removal rate increased from41.8%at6h to63.7%at72h under the initial copper concentration of5mg·L-1. Finally, the removal rate declined from63.8%at instantaneous stage to54.5%at72h under the initial copper concentration of20mg·L-1. High initial removal rate was observed in different treatments of cadmium adsorbed by Chlorella pyrenoidosa, and it declined with the passage of time, and then reached equilibrium finally. The removal rate of lead by Chlorella pyrenoidosa reached a maximum at6h, and the removal rate was76.4%,80.7%,86.8%,87.5%respectively based on the initial concentration of50mg·L-1,100mg·L-1,200mg·L-1,300mg·L-1. The removal rate declined steadily after6h. Additionally, the growth of Chlorella pyrenoidosa was inhibited significantly by copper, cadmium, lead solution alone, and strongest inhibition was found by copper solution at the same concentration. Results also showed that chlorophyll synthesis and soluble protein of Chlorella pyrenoidosa could be inhibited significantly in the presence of copper, cadmium, lead, and SOD activities were activated at low concentration treatment of copper, cadmium, lead.(2) Based on the adsorption experiments of single heavy metal pollution, effects of Chlorella pyrenoidosa on heavy metal removal with different concentration in combined pollution water (Cu+Cd, Cu+Pb, Cd+Pb, Cu+Cd+Pb) were also conducted, and we also explored the effects of combined pollution on the growth characteristics and biochemical composition of algal cells. Results showed that good effects of heavy metal absorbed by Chlorella pyrenoidosa were found in combined pollution water at the initial stage, and in all the treatments of combined pollution, the removal rate of Chlorella pyrenoidosa on heavy metals increased significantly in the presence of lead. For example, in the combined treatment of Cu+Cd (2.5mg·L-1+10mg·L-1), the removal rate of copper was39.5%at72h, while it was82.8%in the treatment of Cu+Pb (2.5mg·L-1+50mg·L-1). In the combined treatment of Cu+Cd (2.5mg·L-1+10mg·L-1), the removal rate of cadmium was42.9%at72h, while it was92.0%in the treatment of Cd+Pb (10mg·L-1+50mg·L-1). And also, the removal rate of three heavy metals was more than80.0%in the different concentrations of Cu+Cd+Pb. At the same time, there was a positive correlation between the inhibition of combined pollution of heavy metals on the growth of Chlorella pyrenoidosa and concentrations of heavy metals. In addition, chlorophyll synthesis and soluble protein of Chlorella pyrenoidosa were significantly inhibited in the presence of combined heavy metals, and SOD activities were activated simultaneously.(3) Effects of Chlorella pyrenoidosa powder on heavy metal removal in single and combined pollution water and the selective between different heavy metals were carried out. Results showed that the removal of copper, cadmium, lead by algae powder was also a rapid process, and there was a good removal rate at initial5min, also the equilibrium was established within about3h, and it was tight enough between algal cells and heavy metal ions. The adsorption effect of heavy metals performs a significant competition in mixed-metal system. In the combined treatment of Cu+Cd (50mg-L-1+50mg·L-1), the removal rate of copper was18.6%at180min, while the removal rate of cadmium was13.1%. In the treatment of Cu+Pb (50mg·L-1+50mg·L-1) and Cd+Pb (50mg·L-1+50mg·L-1), the removal rate of copper and cadmium were12.5%and26.5%, while the removal rate of lead were80.5%and75.5%, respectively. Thermodynamic studies showed that the equilibrium date fitted well with the Langmuir isothermal than the Freundlich isothermal, and the maximum biosorption capacities of algae powder for copper, cadmium and lead were33.784,30.395and172.414mg·g-1, respectively, and the adsorption capacity order for algae powder was:lead> copper> cadmium. (4) Effects of wall-breaking algal powder and lipid extraction algal powder on copper, cadmium, lead removal were carried out in the present study. Results showed that the removal of copper, cadmium and lead by wall-breaking algal powder and lipid extraction algal powder was also a rapid process, and the equilibrium was established within about3h. For example, the removal capacity of copper with different concentrations (5,20,50and80mg·L-1) at180min by wall-breaking algal powder were declined with33.5%,45.3%,62.3%,62.8%than common algal powder. It suggested that the adsorption by wall-breaking algal powder on copper cadmium and lead was not as good as common algae powder. Result of lipid extraction on common algae powder showed that the lipid content of Chlorella pyrenoidosa powder was above17.0%. Compared the adsorption effect with lipid extraction algae powder and common algae powder in the presence of copper (5,20,50and80mg·L-1), the removal capacity of copper at180min by lipid extraction algal powder were1.187,1.006,0.831and1.111times respectively as common algae powder. It indicated that the adsorption by lipid extraction algal powder on copper, cadmium and lead was as good as common algae powder. |
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