Linking floc structure and settling properties to activated sludge population dynamics in an SBR

Abstract

Over a period of 227 days properties of activated sludge grown in an sequencing batch reactor (SBR) operated under stable conditions were analyzed. Settling properties (sludge volume index (SVI)) of the activated sludge were compared with on-line measurements of floc size and size distribution obtained by using a laser light scattering technique (Malvern Mastersizer/S, Malvern, UK), and with measurements of microbial community dynamics analyzed by denaturing gradient gel electrophoresis (DGGE) patterns of 16S rRNA genes. In addition, microscopical observations were used to confirm the results. Three distinct stages in the SBR evolution were observed. In the first stage the structural floc properties showed predominant presence of floc-forming bacteria in the activated sludge. A good correlation between floc size, properties and microbial community evolution was observed. The second stage showed a good balance between floc-forming and filamentous bacteria, with good settling properties and a highly dynamic community in the SBR. In the third stage, an increase in the filamentous bacteria, which became predominant in the system was observed. Again, a good correlation between settling properties and floc size distribution was obtained and a new dominant species was observed in the DGGE patterns, which can be assumed to be a filamentous organism.

PBM and activated sludge flocculation: From experimental data to calibrated model

“…The sludge was then allowed to reflocculate under certain specific conditions of mixing intensity and calcium addition and was circulated through a Mastersizer E (Malvern Instruments, Malvern, U.K.) to obtain on‐line quantitative information about floc structure, floc size distribution (FSD), and their derived equivalent diameters. The measurement technique is based on forward laser‐light diffraction and has been used by other researchers 9, 11–13, 15, 36. The sludge flocs are brought in a laser beam, where they cause forward scattering of the incoming light.…”

A methodological approach for direct quantification of the activated sludge floc size distribution by using different techniques

“…The SBR performance was monitored according to a methodology described by Govoreanu et al (2003). The sludge samples (S1) were characterised by filamentous bulking with a sludge volume index (SVI) of 469 ml/g.…”

Detection of Filamentous Bulking Problems: Developing an Image Analysis System for Sludge Composition Monitoring

“…On the one hand, floc size can be expressed, as the appropriate algorithms for area, perimeter, length, and breadth estimation have been implemented. On the other hand, justification of the implemented set of floc shape measurements is found in literature references and amounts to seven dimensionless descriptors~Grijspeerdt & Verstraete, 1996, 1997da Motta et al, 2001;Heine et al, 2002;Govoreanu et al, 2003!. The aspect ratio~AR!, the roundness~R!, and the reduced radius of gyration~RG! are expected to exhibit a sensitivity to elongation, whereas the form factor~FF!…”