Study On The Preparation Of Bioflocculant And Its Flocculation Effect On Cyanobacteria In Chaohu Lake

Due to the rapid development of the surrounding economy,the eutrophication degree of Chaohu Lake water body is also increasing,which directly leads to the continuous outbreak of cyanobacteria bloom of Chaohu Lake from June to October every year,which destroys the original ecological balance of the water body,seriously endangers the health of the water ecosystem,and then affects the water body safety,and has a serious threat to human health.At present,flocculation sedimentation is the most common and large-scale algae removal method,and it is particularly urgent to develop and use a kind of flocculant with certain flocculation effect and no secondary pollution.In this paper,four kinds of bioflocculants were prepared by using different biomass materials.They are protein(sjzm and sjym),skeleton(sjzg)and plant fiber(JMF)bioflocculants.The four bioflocculants were characterized by FTIR,XRD and SEM.Finally,the flocculation process of the cyanobacteria in Chaohu Lake was explored.The effects of the four kinds of biomass flocculants,the pH of the algae water,the algae density of the cyanobacteria hydration and the particle size of the flocculants on the algae removal were investigated.The flocculation conditions,such as the absorbance removal rate of the supernatant,the algae cell removal rate,the turbidity removal rate of the algae water,the water content of the algae mud after flocculation and the zeta potential,were analyzed.The flocculation effect and mechanism are explored,and the feasibility of practical application is analyzed.The following conclusions are drawn:(1)Four kinds of bioflocculant were added separately for flocculation experiment.The best dosage of the flocculant was about 20% of the absolute dry weight of cyanobacteria.Among them,JMF bioflocculant had the highest absorbance removal rate for supernatant and the best dehydration effect after flocculation,with the removal rate of 44.41% and the lowest water content of 85.09%.Sjzm has the bestflocculation efficiency and turbidity removal rate for algae cells,with flocculation efficiency of 43.77% and turbidity removal rate of 47.98%.(2)The flocculation effect of several biomass flocculants under different pH conditions has a great influence.The optimal pH of sjzm is 4,sjym is 3.5,sjzg is 3.5,JMF is 3.5.There is a threshold value in the pH of the four biomass flocculants,that is,when the pH is less than 6.5,the flocculation rate of cyanobacteria cells increases rapidly.The highest flocculation rate of JMF to algal cells was 90.76%.(3)Change the density of algae to explore the adaptability of four kinds of bioflocculant to the flocculation effect of cyanobacteria bloom with different degrees of eruption.Among them,JMF bioflocculant has the most stable flocculation effect under different density of algae.Compared with other bioflocculant,it is more suitable for the treatment of cyanobacteria bloom with higher degree of eruption.Its removal rate for absorbance is between 80.02%-81.60%,flocculation rate for algal cells is between 76.05%-80.36%,and removal rate for turbidity is stable between80.17%-82.36%.When the algae density is 0.045,the lowest water content of the sludge is 80.36%.(4)When the mesh number of JMF bioflocculant is increased,the flocculation and dehydration effect of cyanobacteria is significantly improved.When the particle size of JMF is increased from 100 mesh to 200 mesh,the removal rate of JMF for the supernatant of cyanobacteria is increased from 55.63% to 80.79%;the removal rate of flocculation for algae cells is increased from 53.32% to 80.43%;the removal rate of turbidity of cyanobacteria is increased from 57.54% to 82.43%;the removal rate of flocculation for the supernatant of cyanobacteria is increased from 55.63% to 80.79%After dehydration,the water content of cyanobacteria sludge also decreased from82.3% to 80.29%.It can be seen that the smaller the particle size is,the better the flocculation and dehydration effect of JMF on cyanobacteria is.(5)The decrease of pH value can increase the number of positive charges in the water,reduce the concentration of negative charges carried by the original algal cell colloidal particles,compress the thickness of the double electric layer,reduce the zeta potential,and the algal cell colloidal particles will combine with the positive andnegative charges of the active groups on the biomass flocculant to form a floc that is easy to separate.The main mechanism of bioflocculant flocculation is neutralization by electricity,bridging by adhesion and sweeping by net.Biomass materials are cheap,easy to get and free of secondary pollution.They can be salvaged together with cyanobacteria flocs to improve their dehydration performance and carry out plate and frame pressure filtration,which has good ecological value.After studying the technological conditions of cyanobacteria flocculation,using the high dry dehydrator and setting parameters,the moisture content of the cake can reach 57.645%.