Effect of floc structure and strength on membrane permeability in the hybrid coagulation-microfiltration process

The relative importance of floc property on microfiltration and fouling mechanism remains a field of arguments. The effects of floc structure and strength on fouling rate of coagulation-microfiltration were investigated in dead-end microfiltration. Flocs varying in size, fractal structure and strength were prepared by AlCl3 and PACl (Polyaluminum Chloride) coagulation at various dosages followed by different slow mixing rates and filtration without any sedimentation step. The rates of flux decline for flocs formed under same coagulant dosage but different shear conditions showed only limited size and compactness dependence. However, the floc strength effect on membrane filtration performance was observed clearly with the floc strength constant exhibiting a strong positive linear correlation with the resulted cake compressibility index.