Microsphere addition for the study of biomass properties and density effects on settleability in biological wastewater treatment systems

Recent research has demonstrated that biomass density can vary in activated sludge systems, and that this can affect biomass settleability. Other factors related to floc structure are well known to affect settleability, and these can also vary considerably across samples. A new method to isolate density effects on sedimentation was developed and applied based on the addition of commercially available, high and low density microspheres. Density was a linear function of microsphere dose in five full-scale samples, and it was negatively correlated with sludge volume index (SVI) values. Density effects on SVI were similar to previous reports where density varied with biomass polyphosphate content. A new method to calculate water content and floc volume was developed and applied, and water content was inversely correlated with density, polyphosphate, and nonvolatile suspended solids. These results suggest microsphere addition may be useful in future studies of biomass sedimentation and other properties. (C) 2007 Elsevier Ltd. All rights reserved.