Study On The Removal Of Algae With Coagulation By Polymeric Aluminum Chloride Compounded With Different Size Of Clay

The harm of algae blooming to the treatment and quality of drinking water has already aroused people's attention. The filter jam caused by algae is all along a hard problem to resolve for water treatment plant. At present the mainly method for purifying water in water treatment plants is coagulation with inorganic polymer flocculants polyaluminum chloride (PAC) .Polyaluminium chloride(PAC) has excellent agglomerate performance and can make floccules grow bigger enough to settle. However, the floccules formed by PAC are too incompact to subside effectively that the aim to separate algae from water availably can not be achieved. Aderson.D.M pointed out on an article published in Nature that coagulation with clay was one of the most promising methods to solve the problem of algae pollution. Studies indicated that clays could do adhere to algae, whereas the floccules were small and difficult to go down when the dosage of clays was less than 60mg/L. In this article, the coagulation processed by compounding PAC, which has well flocculating and subsiding performance, with different size of food additives clay was introduced. The progress had greatly intensified the compactness of flocs and increased its perceptibility. Therefore, it effectively prevented the flocs from floating again and avoided the flocs entering the filter and leading to filter jam. Thus, not only the algae could be removed from water effectively but also the content of Al left and TOC in treated water could be reduced. The content of aluminum species has changed. The contents of suspended aluminum is increased, and the contents of soluble aluminum is decreased.Control the absorbency of the diluted algae solution as 0.030 at 680nm and put 1000ml of the solution into ZR4-6 coagulation experimental blender. The results showed that the removal of algae with different size of clay compounded with PAC has good rules. When the size of clay is 160 and the dosage of PAC and clay are 12mg/L and 24mg/L, the effect of oscillatoria removal is best. The removal rate of turbidity and chlorophyll-a are 98.2% and 100%. The removal of mixed algae needs PAC 14mg/L and clay 24mg/L. The removal rate of turbidity and chlorophyll-a are 96.7% and 98.3%.Considering mechanism, the main function of clays(kaolin) should be to increase the concentration of suspending particles, to promote the colliding opportunity among the particles and to act as the coagulate core of algae and other suspending particles in the process of fast-stirring, which can make the first-level group particle get smaller and thicker according to the model of flocs growth.