Compartmentalization of Metals within the Diverse Colloidal Matrices Comprising Activated Sludge Microbial Flocs
- Gary G. Leppard *ab,
- Ian G. Droppoa,
- M. Marcia Westbc and
- Steven N. Lissd
- a Aquatic Ecosystem Management Research Branch, National Water Research Institute, Burlington, ON, Canada L7R 4A6
b Department of Biology, McMaster University, Hamilton, ON, Canada L8S 4K1
c Faculty of Health Sciences Electron Microscope Facility, McMaster University, Hamilton, ON, Canada L8N 3Z5
d Department of Chemistry, Biology and Chemical Engineering, Ryerson University, Toronto, ON, Canada M5B 2K3
Activated sludge floc from a wastewater treatment system was characterized, with regard to principal structural, chemical, and microbiological components and properties, in relation to contaminant–colloid associations and settling. Multiscale analytical microscopies, in conjunction with multimethod sample preparations, were used correlatively to characterize diverse colloidal matrices within microbial floc. Transmission electron microscopy, in conjunction with energy dispersive spectroscopy (EDS), revealed specific associations of contaminant heavy metals with individual bacterial cells and with extracellular polymeric substances (EPS). Floc structure was mapped from the level of gross morphology down to the nano-scale, and flocs were described with respect to settling properties, size, shape, density, porosity, bound water content, and EPS chemical composition; gross surface properties were also measured for correlation with principal floc features. Compartmentalization results based on 171 EDS analyses and representative high-resolution images showed that nano-scale agglomerations of (i) silver (100%) and (ii) zinc (91%) were confined almost entirely to EPS matrices while (iii) Pb (100%) was confined to intracellular granules and (iv) aluminum was partitioned between EPS matrices (41%) and intracellular matrices (59%). The results suggest that engineered changes in microbial physiology and/or in macromolecular EPS composition may influence metal removal efficiencies.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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