Study On The Removal Of Chlorella Vulgaris By Combined Using PAC And Kaolin

Algal products have great impact on the production of drinking water. Extracellular polymeric substances(EPS),released by algal in waters,could be transfered into toxic byproducts during disinfection. Some of EPS, such as microcystin and anabaenin, are of hepatotoxicity and stimulation of tumour. Excessive amount of algae in the raw water may bring on bad influence: consume more coagulants, clog filter, increase backwashing water, produce stinking odour, and affect the esthetic effect of gas-water interface of purification structure in the open air. Various research and actual operation indicate that using traditional process to get rid of algae is not effective. Therefore, enhanced coagulation is one of a research task for removing algae from raw water.The effect of using several common coagulants to remove chlorella vulgaris selected as represent of algae was compared from multiple aspects in this research. A new idea that using Kaolin as coagulant aid by surface physics and chemistry process to remove C. vulgaris was brought forward in this paper. According to the experiment result, during coagulation the best dosing condition that feeding 20mg/l Kaolin first, dosing 20mg/l PAC after 2 minutes can enhance the structure of flocs, increase the density of flocs, and improve the removal effect.Under variable biological conditions(different growth phase, in dark or nutrient-deficiency) culturing chlorella vulgaris by changing aqueous environmental circumstances (temperature, pH, the cells pretreated with KMnO4 or CuSO4, removing the extracellular compounds with loose substrate surface, the existence of fulvic acid and surfactant sodium dodecyl benzene sulphonate) indicated that this method of using PAC combined with Kaolin to remove algae was reliable, and suitable for variable water circumstance, and its application could be popularizeded in drinking water treatment. Experiment results with raw water also proved that the removal efficiency of C. vulgaris could reach optimistical level by combined using PAC and Kaolin.This paper finally measuredζpotential and proposed that bridging flocculation was the main mechanism of C. vulgaris coagulation with PAC. Photometric Dispersion Analyser (PDA) was also used to reveal the movement trend of floc size with coagulation time according to flocculation dynamic characteristics, and the formation time of best flocs was also determined by PDA. After formation of the best flocs sampling to analyze by scanning electron microscope (SEM) and computing fractal dimension, results microcosmicly demonstrated that the structure of flocs which formed after feeding Kaolin followed PAC was tighten and dense , and was beneficial to coagulation.Clay can be made from abundant resources, and its cost is cheap, moreover, it has no pollution to environment. The method of combining PAC and Kaolin to treat drinking water is simple, low cost and effective, therefore, it is of great benefit to economy and social.