Selection of Dewatering Treatment to Reduce Sludge Volume in Water Potabilization Plants

Abstract

The objective of this study is to determine the effects of a previous treatment by using polymer in sludge dewatering. In this case, three processes were employed: gravity thickening, conditioning with three different polymers (anionic, cationic and no ionic) and acidification. Polymer conditioning followed by acidification was the best to reduce sludge volume (97.6%). However, its dewatering capacity was inferior because the specific resistance to filtration was greater than conditioned sludge. This result was corroborated with zeta potential since particles charges were reduced from -19 to -5 mV which resulted in greater particle agglomeration and water loss in sludge. The cationic polymer was the best to reduce particle charge (-5.7 mV) and when this was acidified, zeta potential dropped to -4.8 mV. Thus a greater particle agglomeration and elimination of free water was possible. In conclusion, to obtain the greatest reduction of sludge it is necessary to use high molecular weight cationic polymer followed by acidification. Acidification modified sludge morphology due to breakings of solid-aluminum hydroxide links which derived in reduced free space between particles causing in turn free waterloss and, in consequence, less sludge volume.