Effect of Delaying the Addition of Polymeric Coagulant-Aid on Settled Water Turbidity

The effect of polymeric coagulant aids and the time of their addition relative to the addition of the primary metal coagulants was investigated in a series of jar tests. Solutions of humic acid were coagulated using iron and aluminum coagulants in conjunction with various commercial polymers. Turbidity, particle size distributions, pH and absorbance of UV light at 254 nm were measured in these experiments. The morphology of flocs was characterized by their fractal dimensions as determined by light scattering as a function of angle. Settled water turbidity appears to be more sensitive to the time of polymer addition when ferric coagulants are used as the primary coagulant in comparison with alum.