Study On Enhanced Coagulation

Enhanced Coagulation (EC) is one of the most economical and effective advanced drinking water treatment technologies. It can effectively remove organic matters and disinfection by-products formation potential (DBPFP) in water without large monetary investment. This paper studied the enhanced coagulation condition and performance of polyferric sulfate (PFS) and aluminum sulfate (AS) by jar tests by using the humic acid and the water from the Huangpu River as the raw water. Also, the coagulation mechamsm of these two coagulants was discussed by the experiments of Zeta potentials measuring, molecular weight distribution and flocs's fractal dimension measuring.Experimental results showed that: For both the humic acid and the Huangpu River water, the adjusting of the dosage of the two coagulants and pH in raw water can improve AS and PFS's performance of removing turbidity and organic matter, but adding the polyacrylamide can not get an obvious improvement. The improvement by adding the PFS was 15%-20% higher than that of AS in terms of removing the organic matter under the same conditions. By studying the relevant Zeta potentials it can be concluded that the coagulation mechanism of PFS was mainly adsorption bridging while the AS charge-neutralization. Through the PFS orthogonal test the primary and secondary order of the influence factors and the best factors' level about the coagulation capability of PFS were confirmed. And the experimental results for the water from the Huangpu River showed that EC can improve the effect of removing the chroma, manganese and iron in the water and control the dosage of the residual coagulant effectively.Data got from molecular weight distribution showed that: (1) PFS is more effective than AS in removing the small molecular weight of organics, but these two coagulants chiefly remove the macromolecule of organics in the mass. (2) Water conditions have effect on the coagulant's removing the different molecular weight distribution of organics. (3) Powder activated carbon (PAC) can remove the smallmolecular weight of organics but almost cannot deal with the macromolecule of organics. (4) PFS and AS removed the small molecular weight of organics much more efficiently when being used with the PAC respectively, sharing almost the same efficiency.At the same time, the flocs's fractal dimension of the two coagulants was tested in different coagulation conditions. The result showed that the flocs's fractal dimension of AS was easily changed when the dosage of AS and pH varied. The biggest flocs's fractal dimension was about 1.7-2.2and the smallest was about 1.2-1.6. On the contrary, varying the dosage of PFS and pH can not change the flocs's fractal dimension of PFS a lot. Furthermore, its fractal dimension is about 1.4-1.6 and is smaller than that of AS. Adding PAC can not change the flocs's fractal dimension of AS effectively but advance sharply the flocs's fractal dimension of PFS to about 2.0. However, adding of PAM can not obviously affect the flocs's fractal dimension of these two kinds of coagulants.