Flocculation And Removal Of Algae In Eutrophication Water Body By Modified Clays

The application of composite flocculants was focused on. Using chitosan or polymeric aluminum ferric chloride (PAFC) composite to twelve clays treated high algae content lake water. The turbidity as well as the chlorophyll-a before and after the treatment are compared and analyzed to investigate the composite flocculants performance, and obtained the optimum parameters of composite flocculants by experiment.The results show that the algal removal efficiency was greatly improved after the modification of the clays. Among the clays studied, high viscosity attapulgite was most efficient toward algae removal. The optimum total loading of chitosan-modified high viscosity attapulgite was 29.4mg·L-1 and the corresponding chlorophyll-a removal rate and turbidity removal rate were 96.2%, 95.61% respectively to I#. The optimum total loading of chitosan-modified high viscosity attapulgite was 66mg·L-1 and the corresponding chlorophyll-a removal rate were 95.45% to II#. The best ratio between Chitosan and clay is various to different types of water bodies. Compared with chitosan, the chitosan-modified clays increased flocs density, reduced flocs volume, and improved flocs distribution. The chitosan-modified clays with particle size ranging from 18μm to 150μm, difference between the removal rate of turbidity and chlorophyll were 0.4% and 2.7%, indicating particle size of clays had little influence on the removal of algae. The algal removal efficiency was higher in acidic conditions, while declined rapidly with the increase of pH in alkaline conditions.Using polymeric aluminum ferric chloride (PAFC) composite to twelve clays treated high algae content lake water had been first studied. The results show that the optimum total loading of PAFC-modified clay was 9.18mg·L-1 (total dosage was 69.18mg·L-1) to I#, less than the dosage of PAFC adding only (12.24mg·L-1). The corresponding chlorophyll-αremoval rate and turbidity removal rate were 93.75%, 90.09% (white clay) and 90.63%, 93.18% (diatomite) respectively. The optimum total loading of PAFC-modified clay was 40.8mg·L-1 to II#, (total dosage was 120.8mg·L-1), less than the dosage of PAFC adding only (61.2mg·L-1). The corresponding chlorophyll-a removal rate and turbidity removal rate were 98.80%, 91.32% (white clay) and 96.39%, 90.08% (diatomite) respectively. Compare with PAFC alone, the PAFC-modified clays increased density of flocs, reduced volume flocs, and improved even size distribution of flocs. The algal removal efficiency was higher when the pH value was 3-8. The appropriate rapid stirring speed was 300rpm and stirring time was 2min. And the appropriate slow stirring speed was 30rpm and stirring time was 15min. The proper feeding order is clay added firstly and then addition of PAFC.