| In water and waste water treatment, flocculation is one of the most important units, which has a significant impact on the subsequent operating conditions, the water quality of outflow and the cost of water treatment to a great extent. Flocculation process is used to change particle size distribution of suspension, and units of sedimentation and filtration can only remove particles of a certain grain size range;the regular coagulants and coagulation process can not satisfy the new standard of drinking water for orgnanic micropollutants; the low dose of poly aluminium chloride is difficult to achieve the desired flocculation efficiency in winter water; therefore, using coagulant aid which has the advantage of high efficiency, low cost and no side effect in the flocculation process is very important.Newly formed manganese dioxide was prepared by manganese sulfate and potassium permanganate through redox reaction, it can improve the effect significantly in the process of coagulation of water treatment. The particle size of newly formed manganese dioxide is extremely small, it can contact Fe3+, Al3+(and its hydrolysis products) fully, and can promote the growth of floc by adsorption, it has the advantage of simple preparation method,convenience and no side effect ect, so it is economically and technically feasible in water treatment.In this thesis, poly aluminium chloride was taken as flocculant, the newly formed manganese dioxide was taken as coagulant aid and suspended particles of Kaolin and humic acid were regarded as the removal target, on-line turbidimeter and particle counter were used to monitor the flocculation process and record data. The results showed that, the newly formed manganese dioxide as coagulant aid can improve the removal of particle significantly, organics were mainly removed in the process of micro-flocculation; the removal rate of UV254 and particle in settled water were 64.38% and 12.19% respectively with 0.03mmol·L-1 newly formed manganese dioxide; while UV254 and particle can be removed as high as 66.67% and 70.60% as the newly formed manganese dioxide (0.03mmol·L-1)enhanced the coagulation of poly aluminium chloride(20mg·L-1).Fractal theory was introduced into the characteristics of newly formed manganese dioxide floc size distribution, the results showed that the floc size distribution has fractal nature, and this index could quantify the influence force of particle size distribution on flocculation efficiency under different flocculation conditions,the faster rate of change of its value and the earlier extreme in the newly formed manganese dioxide flocculation process, the corresponding flocculation efficiency is better, the results also displayed that there was a good correlation between fractal dimension of floc size distribution in the stage of micro-flocculation and the end of flocculation and less than 5μm particle population in settled water,residual turbidity, the index can reflect the flocculation efficiency very well. Therefore, according to the change of fractal dimension can adjust the dosage timely to meet the requirements of follow-up processes.Besides, on-line particle counter was used to monitor the quality of filtered water continuously, the results showed that, the filtered water had similar particle size distribution and less than 5μm particle population mainly when flocculation conditions were changed; quality of settled water has a certain impact on quality of filtered water, however, 5μm particle population has a greater impact on the filtered water quality, by controlling floc size distribution in the process of flocuulation can control 5μm particle population in settled water, accordingly can improve filtered water quality and water supply security.
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