title: Characterization of activated sludge flocs by confocal laser scanning microscopy and image analysis.
abstract: In this study we present a new approach to determine volumes, heterogeneity factors, and compositions of the bacterial population of activated sludge flocs by 3D confocal imaging. After staining the fresh flocs with fluorescein-isothiocyanate, 75 stacks of images (containing approx. 3000 flocs) were acquired with a confocal laser scanning microscope. The self-developed macro 3D volume and surface determination for the KS 400 software package combined the images of one stack to a 3D image and calculated the real floc volume and surface. We determined heterogeneity factors like the ratio of real floc surface to the surface of a sphere with the respective volume and the fractal dimension (D(f)). According to their significant influence on floc integrity and quality, we also investigated the chemical composition of flocs and quantified their bacterial population structure by using group-specific rRNA-targeted probes for fluorescence in situ hybridization. By a settling experiment we enriched flocs with poor settling properties and determined the above-mentioned parameters. This approach revealed shifts in floc volume, heterogeneity, and bacterial and chemical composition according to the settling quality of the flocs.
authors.affiliation: Lehrstuhl für Mikrobiologie, Technische Universität München, Am Hochanger 4, D-85350 Freising, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Schmid
authors.forename: Antoine
authors.initials: A
authors.lastname: Thill
authors.forename: Ulrike
authors.initials: U
authors.lastname: Purkhold
authors.forename: Marion
authors.initials: M
authors.lastname: Walcher
authors.forename: Jean Yves
authors.initials: JY
authors.lastname: Bottero
authors.forename: Philippe
authors.initials: P
authors.lastname: Ginestet
authors.forename: Per Halkjaer
authors.initials: PH
authors.lastname: Nielsen
authors.forename: Stefan
authors.initials: S
authors.lastname: Wuertz
authors.forename: Michael
authors.initials: M
authors.lastname: Wagner
mesh_terms: D001419:Bacteria; D004269:DNA, Bacterial; D004784:Environmental Monitoring / Q000379:methods*; D005427:Flocculation; D017404:In Situ Hybridization, Fluorescence; D018613:Microscopy, Confocal; D011157:Population Dynamics; D012722:Sewage / Q000737:chemistry*
chemical_list: D004269:DNA, Bacterial; D012722:Sewage