A comprehensive insight into floc characteristics and their impact on compressibility and settleability of activated sludge

This paper presents a comprehensive study of sludge floc characteristics and their impact on compressibility and settleability of activated sludge in full scale wastewater treatment processes. The sludge flocs were characterised by morphological (floc size distribution, fractal dimension, filament index), physical (flocculating ability, viscosity, hydrophobicity and surface charge) and chemical (polymeric constituents and metal content) parameters. Compressibility and settleability were defined in terms of the sludge volume index (SVI) and zone settling velocity (ZSV). The floc morphological and physical properties had important influence on the sludge compressibility and settleability. Sludges containing large flocs and high quantities of filaments, corresponding to lower values of fractal dimension (D-f), demonstrated poor compressibility and settleability. Sludge flocs with high flocculating ability had lower SVI and higher ZSV, whereas high values of hydrophobicity, negative surface charge and viscosity of the sludge flocs correlated to high SVI and low ZSV. The quantity of the polymeric compounds protein. humic substances and carbohydrate in the sludge and the extracted extracellular polymeric substances (EPS) had significant positive correlations with SVI. The ZSV was quantitatively independent of the polymeric constituents. High concentrations of the extracted EPS were related to poor compressibility and settleability. The cationic ions Ca, Mg, Al and Fe in the sludge improved significantly the sludge compressibility and settleability. (C) 2003 Elsevier Science B.V. All rights reserved.

Trends in physical activity participation and the impact of integrated campaigns among Australian adults, 1997-99

Objectives: To determine whether awareness of the moderate physical activity message and prevalence of participation changed among Australian adults between 1997 and 1999, and if changes differed across Australia. Methods: Data were compared on awareness of the moderate physical activity message and on physical activity participation from identical national physical activity surveys in 1997 and 1999. Results: In 1999, following integrated public health efforts, recognition of the Active Australia campaign was substantially higher in NSW/ACT (61.7%) than elsewhere (29.3%). Knowledge about benefits of moderate activity increased between 1997 and 1999, more so in States with public health campaigns. National participation in 'sufficient physical activity' declined between 1997 and 1999, from 63% to 57%, but the decline was smaller in NSW/ACT (4.4%) than in the other States (6.0%). Conclusions and implications: Declining trends in physical activity in Australia require increased public health investments, including strategic planning and public education, such as occurred in NSW (1997/98).