Study On Floc Breakage And Re-growth

Coagulation has been paid much attention as the core part in the research of water treatment, however, the mechanism research of which is still not completed well. This paper has a further research to the coagulation mechanism. The main parts are the initial size of nanoparticles research in water and their bonding ways and corresponding capacity analysis in re-flocculation process after the floc fragmentation, as well as the influencing factors of final growth floc size and morphology, regenerate ability after crushing. In this paper a laser diffraction instrument (Malvern Mastersizer2000, Malvern, U.K.) was used to measure dynamic floc size as the floc flocculation and flocculation process proceeded.The test results can reflect the flocs formation breakage and re-growth ability. This paper has made concrete analysis of research on the floc fragmentation and re-flocculation ability under the different conditions of iron/aluminum ratio, mixing process, addition of PAM and anion type.The results showed that:(1)The area of floc formation is affected by pH value, and iron/aluminum ratio. Coagulation mechanisms of iron, iron/aluminum. aluminum are different at different pH values. The plateau d50value decreased as the Fe/Al ratio decreased, and the ratio of2:3was the inflection point. If Fe/Al ratio was lower than2:3. plateau d50decreased little or even increased. The breakage factor of flocs was higher at low pH when the flocs formed with high Fe/Al ratio, and was lower at low pH when the flocs formed with low Fe/Al ratio.(2) There is no significant effect on flocculation and Re-flocculation after breakage of flocs and the sweep coagulation dominated when the PAM and alum dosing at the same time. Flocculation ability and re-flocculation ability after crushing increase as flocculation time or PAM dosage increase.(3) The plateau d50value of alum or PACl25flocs by806050rpm was lower than the one formed by50rpm. For both of them, there was significant irreversibility of broken flocs. On the contrary, there is no difference between these two mixng condition for the plateau d50value of FeCl3flocs, except the increasing speed is higher by806050rpm. For FeCl3, the duration of breakage time significantly vary the re-growth ability of broken time. The floc fragmentation and different mixing conditions have no obvious effect on the residual coagulant concentration.(4) Different concentration and species of anions caused different size of primary particles, zeta potential of flocs and flocs size. As the concentration of SO42-and PO43-increase, the size of the primary particles become larger, but zeta potential value decreased; while there is no change by Cl-. Different species of anions caused different maximum size of flocs. The fractal dimension of flocs decreased as the concentration of flocs increased at pH6～7with SO42-and PO43-, while it changed little by Cl". Residual Al is just determined by the pH, and independent on the concentration and species of anions.