Removal Effects And Mechanism Of Compound Heavy Metals In Secondary Effluent By Chlorella Vulgaris

The use of biological methods to remove heavy metal ions from wastewater is a hotspot and a difficult point in the field of environmental science and engineering.This topic chooses to use the active Chlorella vulgaris in biological methods to achieve the treatment of heavy metal sewage.This subject first studied the removal effects and optimal removal conditions of the five kinds of heavy metals(Cr?As?Zn?Fe?Mn)in the secondary effluent by Chlorella vulgaris and on this basis studied the removal effects and adsorption characteristics of every kind among the three kinds of heavy metal(Cr?Zn?Fe)by Chlorella vulgaris in the secondary effluent and the accompanying physiological changes and finally the removal effect and adsorption mechanism in the coexistence of Cr and Zn by Chlorella vulgaris were investigated.The characteristic of this subject is that the selected sewage is the actual sewage–the secondary effluent of a municipal sewage treatment plant instead of common simulated wastewater,which is relatively rare in previous studies.Some of the major conclusions obtained in experiments were as follows:(1)The water quality of the secondary effluent from the municipal sewage treatment plant can meet the normal growth of Chlorella vulgaris.The changes of initial p H of the medium,initial algae density and illumination time had certain effects on the growth state of chlorella.When p H=7,illumination time was 12 h,initial algae density was 4×105 cells/m L,the algae density reached the maximum.The removal effect by Chlorella vulgaris on the Fe,Mn,Zn,Cr,As from secondary effluent had a certain relationship with the initial p H value of the culture medium,the initial inoculation algae density and the illumination time.When p H=7,illumination time was24 h,and initial algae density was 4×105 cells/m L,the total adsorption of five heavy metals by Chlorella vulgaris reached the maximum;(2)The presence of Cr,Zn and Fe alone inhibits the growth of Chlorella vulgaris,and the inhibition increases with the increase of heavy metal concentration,by measuring the algae density and photosynthetic pigment content it can be found that the greater the concentration of heavy metals,the slower the rate of propagation of chlorella and the lower the maximum algal density during the growth cycle;Low concentrations of heavy metals can promote SOD activity in algae,but high concentrations of heavy metals inhibit SOD activity;The content of MDA in algae cells has been increasing with the increase of heavy metal concentration;The adsorption of Zn,Fe and low concentration of Cr by Chlorella vulgaris is a rapid adsorption process,and the adsorption effect is good and there is not obvious desorption phenomenon,however,for high concentration Cr(concentration ?0.5mg/L),it is a process of slowly adsorbing and then abruptly increasing the adsorption amount,and the adsorption effect is poor,the removal rate is less than 20%and there is a desorption phenomenon.(3)For the removal of compound Cr and Zn in the secondary effluent by Chlorella vulgaris,the presence of Cr in the water will significantly inhibit the adsorption of Zn by Chlorella vulgaris,while the concentration of Zn has little effect on the adsorption of Cr;The activity of SOD in Chlorella vulgaris cells increased with the increase of heavy metal concentration,but when the heavy metal stress exceeded a certain limit,the activity of SOD began to decrease;the content of MDA in Chlorella vulgaris cells was positively correlated with the concentration of heavy metals.The higher the concentration of heavy metals,the higher the content of MDA in algae.