Use of a superthickener device to concentrate potable water sludge

A superthickening device (solids bed height=5.5–6.0 m) has been examined for potential use in concentrating an alum-based sludge generated during the production of potable water. Initial trials show that, even when flocculated using an appropriate dose of polyelectrolyte, the superthickened sludge settles to a solids content of only 3–4 wt%. This concentration is equivalent to the sludge gel point and indicates that no significant sediment-based compression is taking place. However, when subjected to an in situ low shear rate (1 rpm) stirring treatment, the polyelectrolyte-flocculated sludge consolidates to far higher concentrations, reaching 17 wt% solids after 60 h of thickening. Possible mechanisms underlying this result include the rearrangement and densification of the inter-particle network and suppression of liquid channels in the sediment bed. On a more qualitative level, this study also briefly considers the advantages of superthickeners over conventional mechanical dewatering methods and outlines a number of experimental considerations relevant to future research.