Study On The Enhanced Coagulation Removal Of Microsystis Aeruginosa From Water

Microcystis aeruginosa 905 was selected as experimental material in this study, for it was commonly found in a variety of eutrophication of water bodies, at the last growth stage, it may release microcystins(MCs) into the water. MCs has a strong role in inducing liver tumor, and its chemical property was stable, so it had a threat to people's health. Traditional water treatment was not effect to remove algae. Therefor, further study was required to enhance algae removal efficency and microcystins from raw water.A algae removal efficiency of several common flocculants was compared. It was proved that Polyaluminum Chloride (PAC) was more effective than any other tested flocculants. And through a series of tests, we proved the effectiveness of adding kaolin and determined the reasonable adding order of PAC and Kaolin. The results showed that the coagulation stage, the first adding 20mg/L kaolin, following by adding 20mg/L PAC after 2 min slow stirring, the algal removal efficiency could reach 92% and the residual turbidity was less than 1.0 NTU after 30 min settling. Through L9 (3³) orthogonal test it was showed that the pH value of water bodies has greater influence than the dosage of kaolin and PAC. Algae removal efficency is higher at higher pH. Excessive reproduction of algae lead water body present alkaline, which is favorable for algae removal.At a series of negative factors exist, such as continuous illumination, the temperature is too high or too low, there is surfactant, humus, as well as extracellular compounds, although a slight decrease in removal efficiency, but still maintain a high level, it was prove that combining PAC and kaolin to removal algae has a stability effection, so it has practical value.If PAC was used as a main flocculant with kaolin and FeCl₃ as pre- and post-flocculant aids, it is thus suggested that FeCl₃ could be added in 3 min after flocculation with 1mg/L as an optimum dosage. The results showed that the high charge of molysite gather negative charge small floc remaining in the water, and increase the density of flocs, increase the floc density through coating kaolin into the floc, and promote the rapid settlement of floc. At the same time it could reduce the dosage of aluminum which has potential harm to human beings, and reduce the residual turbidity of the water body. By further tests it was proved that adding powdered activated carbon for the removal of Microcystis aeruginosa has a role.Finally, Photometric Dispersion Analyser(PDA)was used to reveal the movement trend of floc size with coagulation time according to flocculation dynamic characteristics, and the best coagulant dosage and the adding sequence were also determined by PDA. After formation of the best flocs sampling to analyze by scanning electron microscope (SEM) and computing fractal dimension, it was pilot study the mechanism of remove Microcystis aeruginosa with kaolin and FeCl₃ as pre-and past- flocculant aids.As a natural adsorbent, Kaolin can be made from abundance resource, and it is low cost, pollution-free, are the preferred flocculant at home and abroad to treat the natural red tide flocculant. The method of combing PAC, Kaolin and FeCl₃ to remove algae is highly promising for is low cost, high efficiency, easy to operate and more safety of drinking water.