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Abstract
The influent ratio of Mono- over Polyvalent cations (M/P ratio) influences activated sludge bioflocculation. A more thorough insight through means of conventional macroscopic parameters, Sludge Volume Index (SVI), and Effluent Suspended Solids (ESS), and microscopic image analysis was pursued in this work. Therefore, a long term experiment was conducted during which activated sludge was exposed twice to a transition in influent M/P ratio from 1.5 to 15. Two distinct observations were made. The first transition indicates the existence of a loosely attached layer evidenced by the temporary release of small sludge particles as observed by image analysis. This release was followed by a decrease in the amount of small sludge particles and increase in floc size indicating good bioflocculated sludge. The second transition results in a massive release of small particles leading to complete sludge deflocculation. (De)flocculation was monitored by both SVI and microscopic image analysis, whereas during the first transition the change in bioflocculation condition could only cleary be monitored by means of microscopic image analysis. Based on this study, microscopic image analysis proves to be a powerful monitoring tool to assess the bioflocculation condition of the activated sludge, whereas SVI is unable to accurately monitor its bioflocculation condition.
ACKNOWLEDGEMENTS
Jan Van Dierdonck is a doctoral student whose research has been financed by the Institute for the Promotion of Innovation by Science and Technology in Flanders (IWT Flanders) IWT-SB/81355. Rob Van den Broeck is supported by the postdoctoral grant PDMK/11/108 from the KU Leuven Research Fund. The work is further supported by Projects IDO/06/008, OT/10/035, SCORES4CHEM KP/09/005 and the Belgian Program on Interuniversity Poles of Attraction, initiated by the Belgian Federal Science Policy Office. J. Van Impe holds the chair Safety Engineering sponsored by the Belgian chemistry and life sciences federation essenscia. The scientific responsibility is assumed by its authors.