Enhancement of the Escherichia coli floe strength with water soluble polymers

The floe strength of Escherichia coli was enhanced by adding water soluble polymer flocculants (BPA-5020 and BPA-5000) to the particulate flocculant (BPA-1000) as indicated by the increase in the shear index. The shear index of the E. coli flocs increased from 0.39 with the particulate flocculant alone to 0.94 with the particulate flocculant in conjunction with the water soluble polymer flocculant. In addition, the sedimentation rate of flocs was higher and the sedimented volume of flocs was smaller when the particulate flocculant was used with the water soluble polymer flocculant. When E. coli was flocculated first with the water soluble flocculant and the particulate flocculant was added later into the E. coli flocs formed, the sedimentation rate of the flocs was greater than that of any other combination. The shear index of the flocs was, however, independent of the sequence of the flocculant addition.