The Research Of Enhanced Coagulation To Remove Cyanobacteri By Hydrochloric Acid Modified Fly Ash

In recent years,the problem of water pollution from drinking water sources has gradually intensified in China.Because of the eutrophication of lakes and reservoirs,the algae bloom is frequent,and the safety of people's water supply security is effected.Therefore,it is very urgent to study efficient and economical algae removal techniques.Based on the traditional coagulation process,the effects of enhanced coagulation and algae removal by modification of hydrochloric acid modified fly ash?FA-HCl?was investigated.The effects of dosage,algae density,extracellular secretion?EOM?,sedimentation time and algal growth period on algae removal were investigated,and optimized the conditions of enhanced coagulation to remove algae and analyzed the mechanism of coagulation and algae removal by hydrochloric acid modified fly ash.The following conclusions are obtained:?1?Taking Microcystis flos-aquae suspension as the object,different modification methods are used to modify fly ash and search a better method for removing algae.The results showed that the removal rate of algae by fly ash was between 10%¹5%.Comparison of different modification methods to remove algae for fly ash:hydrochloric acid>sulfuric acid>high temperature>ultrasonic>NaOH,when the concentration of hydrochloric acid is 15.0%and the dosage is 90 mg/L,the algae removal rate could reached the maximum by hydrochloric acid modified fly ash,and the algae density,turbidity,and chlorophyll-a removal rates could reach100%,98.87%,and 100%.?2?The analysis of enhanced coagulation and algae removal efficiency showed that when the dosage of hydrochloric acid modified fly ash is 80 mg/L and the algae density is A₆₈₀?0.1,the removal rate of algae could over 93%.Under this condition,when the sedimentation time is 40minutes,the algae density,turbidity,and removal rates of chlorophyll-a could reach 97.67%,97.89%,100%.When the algal cells grew from late stage to late stage of decline,the DOC content increased from 10.02 mg/L to 85.91 mg/L.When the dosage of hydrochloric acid modified fly ash is constant,comparing the removal rates of algae in different growth periods,it could found that the removal rate of algae in the logarithmic phase could reach the maximum,and the algae density,turbidity,and chlorophyll-a removal rates could reach 97.09%,98.67%,and 100%.The removal rate of algal is decreased to about 40%in the stage of decline,and this indicates that a small amount of EOM has a promoting effect on flocculation,and excessive EOM will strongly interfere with coagulation.?3?The Response Surface Methodology?RSM?showed that the optimum conditions for the coagulation and removal of algae by hydrochloric acid modified fly ash are as follows:dosage,settling time,and EOM are 113 mg/L,50 minutes,and 11 mg/L.The significant influence factors of UV₂₅₄ model are dosage of hydrochloric acid modified fly ash>sedimentation time>EOM.The significant influence factors on the chlorophyll-a model are dosage of hydrochloric acid modified fly ash>EOM>sedimentation time.?4?Analysing the mechanism of algae removal in coagulation by hydrochloric acid modified fly ash,it is found that the surface voids are increased of acid modified fly ash,which increased its specific surface area.The analysis of the morphology showed that algae flocs by hydrochloric acid modified fly ash is larger and denser than fly ash,and there is a phenomenon of binding and agglomeration.The analysis of Zeta potential showed that there is a significant compression double layer phenomenon in the coagulation process of algal cells before the decline stage.After growth to decline,the algae cells secrete a large amount of EOM on the surface,which makes the electronegativity in algal fluids stronger.Under the same modified fly ash dosage,excessive EOM inhibits the flocculation effect and makes the coagulant algae removal effect.