The Characteristics And Mechanism Of Organically Modified Alum Sludge On Microcystis Aeruginosa Removal

The excessive growth of algae in freshwater has brought a serious hazard to the aquatic ecosystem and the health of nearby residents.There are many methods to remove algae,and the clay flocculation is the most promising method.On the other hand,The alum sludge as a inevitable by-product of the water supply plant,has been approved with good adsorption and sedimentation performance,and can be used as a good sinking carrier instead of clay.Therefore,in this study,Hexadecyl trimethyl ammonium bromide(CTAB)and chitosan,two organic surfactants,was used to modify alum sludge for the first time,and was used to flocculate and remove Microcystis aeruginosa from common algal blooms.The main conclusions are as follows:The experimental study on coagulation and algal removal of CTAB modified alum sludge showed that,the alum sludge with a particle size of 200-300 mesh and calcination at600℃could reach the adsorption equilibrium of CTAB in about 10 min,and the maximum adsorption capacity was 9.2 mg/g.The adsorption process is affected by the specific surface area and porosity of alum sludge,and heat treatment of alum sludge can greatly improve the adsorption performance of CTAB.For algal water with an algal density of 4.88×10~6cells/m L,the optimal dosage of CTAB modified alum sludge was 3.0 g/L,and the algal density and turbidity removal rates were 92.36%and 87.94%respectively after 24 hours.The method of adding alum sludge and CTAB after adsorption balance could achieve the best algae removal effect,and the p H value can be applied in a wide range,but the disadvantage is that the algae removal takes a long time and the dosage is large.The experimental study on coagulation and algal removal of chitosan modified alum sludge showed that,the composite of chitosan and alum sludge with particle size of 200-300mesh and calcined at 300℃at a mass ratio of 1:50 showed good algal removal ability.For algal water with an algal density of 4.88×10~6cells/m L,the optimal dosage of chitosan modified alum sludge was 0.25g/L,and the algal density and turbidity removal rates were100%and 98.92%respectively after 30 mins.The floc was completely compact and the fractal dimension was 1.719.After the response surface method was used to optimize the flocculation conditions,the algae density removal rate was 100%,turbidity removal rate was99.96%,and the fractal dimension value was 1.722.The flocculation and algal removal process of chitosan-modified alum sludge mainly depends on the effect of"electrical neutralization"and"adsorption bridging"of chitosan.The algal removal effect is ideal,fast and efficient,and the amount of addition is small,but the disadvantage is that it requires high environmental p H.After modified by CTAB and chitosan on alum sludge,it will not affect the good phosphorus absorption performance of alum sludge,but also has a certain promotion effect,which can make alum sludge reach the adsorption balance of phosphorus faster.In summary,the modified alum sludge has a good effect of algae removal,can replace clay for algal bloom management,but also provides a new idea for the resource utilization of alum sludge,which has practical application value.