Effects of mixing conditions on floc breakage and re-growth formed by magnesium hydroxide and polyacrylamide

Polyacrylamide (PAM) compounding with magnesium hydroxide as dual-coagulant for treat- ing reactive orange simulated wastewater was studied in this paper. Effects of mixing conditions on floc properties, breakage and re-growth were evaluated through floc size distribution, zeta potential, scanning electron microscopy and Fourier-transform infrared spectroscopy. The aggregation and breakup of flocs showed that there was an increase of floc size and strength under proper shear. When floc size reached to 62.30 µ m at slow mixing period, then breakage at 300 rpm for 60 s, at next slow period at 60 rpm for 3 min, the floc size increased to 78.75 µ m. Flocs re-grew rapidly after breakage and sedimentation time was reduced to 40 s. All of the flocs under investigation showed a strong capacity to re-growth when they had been previously broken. During dual-coag- ulant system, adsorption of magnesium hydroxide and bringing function of PAM were the mainly coagulation mechanisms for reactive orange K-GN removal.

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