Study On The Mechanism Of Multi-flocculation

Flocculation plays a very important role in the supply water treatment process, which will influence the following treatments like sedimentation and filtration, and thus has an effect on the quality of the final effluent. A lot of studies have been conducted on the flocculation processes and the flocculants, but fewer were done on the multi-flocculation and the addition of flocculants.In this paper, we proposed the concept of multi-flocculation and a way to multipoint add flocculants on the basis of a systematic introduction to the mechanism of flocculation, flocculation morphology and flocculation kinetics, aiming at figuring out its feasibility and practical significance through exploring this new approach of flocculation.The experiments were divided into two parts:the first part was a static experiment, in which the turbidity removal efficiency and fractal dimension variation in multipoint dosing method and the traditional way were studied comparatively in different dosing and mixing conditions, using ordinary clay suspension different turbidities (15NTU,20NTU,100NTU,250NTU) as the raw water, and PAC as the flocculants. After confirming the optimal PAC dose, a set of L9 orthogonal tests were conducted to study the impact of multiple factors. Finally, mathematical models of turbidity removal rate in multiple-dosing method and the traditional way were set concerning its relationship with flocculants dosage and mixing conditions as the turbidities of raw water vary. The results showed that:the turbidity removal rate of multiple-dosing method is higher than that of the traditional way in high-turbidity raw water, but lower in low-turbidity raw water.The second part was dynamic tests of coagulation, in which a comparative study of the turbidity removal rate variation in multiple-coagulation dosing column and the traditional dosage column was made,with clay suspension of 50±10NTU used as the raw water, and PAC in different dosages (20,25,30,35,40mg/L) as the flocculants. After that, mathematical models of turbidity removal rate in multiple-dosing method and the traditional way were set concerning its relationship with the dosages of flocculants.The results showed that the turbidity removal rate was the highest in traditional dosing method when the dosage was 25 mg/L; and the turbidity removal rate was the highest in the multi-dosing method when the dosages was 30 mg/L. The results of comparative tests showed that multiple-dosing method was efficient, with water turbidity below 10NTU, and it could completely meet the requirements of filter in water quality.