Removal of Mineral Ions from Water by
Microbially Produced Polymers
PATRICK R. DUGAN
HARVEY M. PICKRUM
Department of Microbiology
The Ohio State University
Columbus, Ohio
INTRODUCTION
As an introduction to this report we would like to review some of our past work in an
effort to substantiate the point of view, that it is possible to develop a practical
microbiological process for removal of many mineral ion contaminants of water effluents.
We present this paper partially as a review of our data because we believe that much of the
microbiological literature is titled in such a way as to preclude those individuals interested
in functional removal processes from reading it.
Aerobic biological waste treatment processes currently in use are largely dependent
upon two biological events: (A) Conversion of dissolved or suspended organic substances to
microbial biomass via oxidative metabolic processes; and (B) The aggregation or
flocculation of the biomass formed, which results in settling, thereby providing a means for
mechanically separating cells from supernatant (i.e. separating sludge from liquor).
We have, for the past several years, been examining the functional role and ecological
significance of extracellular microbial polymers and this requires a study of the biological
reactions concerned with the nutrition, metabolism and synthesis of the polymers. These
considerations evolved into a study of the bioflocculation phenomenon and prompted an
examination of the physio-chemical interractions among organisms and the dissolved or
suspended solids in their environments. The bioflocculation process is emphasized because
of its direct involvement with ion adsorption.
Among the conclusions reached by us and other investigators is that bioflocculation is
intimately related to the synthesis and presence of extracellular polymer fibrils (1,2,3,4,5,6).
In relation to aerobic waste treatment, excess carbon substrates (i.e. dissolved organic) are
converted to extracellular polymer and the extent of polymer synthesis can be manipulated
by altering the carbon to nitrogen ratio of the nutrients (7).
All floc-forming microorganisms studied have either structurally or chemically
different polymers. The chemical composition and structural linkage of monomeric units
determines the physical and chemical properties of the extracellular polymers from
individual species (and even strains of the same species) of organisms. These properties then
determine the observed properties and chemical behavior in solution or suspension. That is,
some polymers are more soluble than others, and some bind water to a greater extent than
others. The more soluble extracellular polymers and the polymers which have a greater
propensity to orient water, which slough off cells and remain in colloidal suspension will
result in increased viscosity of the surrounding solution when produced extensively by cells.
By comparison the polymer properties may be such that the polymer remains as a loose
slime layer in the vicinity of the cells, or it may remain as a well defined capsule or a
zoogloeal matrix around the cells which synthesize it. The key feature in bioflocculation
appears to be synthesis of relatively insoluble extracellular polymer strands so that they
remain in the vicinity of cells and do not dissolve away. In this manner, cells and other
particulate materials become entangled into a flocculent conglomerate on a microscopic
level. The photographs shown in Figures 1 through 9 demonstrate the insoluble
polysaccharide strands around floes of bacteria. The polymer strands were photographed
under ultraviolet illumination after floes were stained with the fluorescent dye paper white,
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