Geosmin is naturally produced by numerous cyanobacteria and actinomycetes in surface
waters. Although it is non-toxic, it causes an unpleasant taste and odor even at very low
concentrations. Water utilities, therefore, often must expend great effort and funds to remove
geosmin to avoid customer complaints when the compound is present in the source water. Saint
Paul Regional Water Services in St. Paul, MN successfully uses granular activated carbon (GAC)
filters to remove geosmin from its drinking water, but, curiously, the useful life of their full-scale
GAC filters has exceeded estimates based on batch sorption isotherms and AdDesignS modeling.
It has been hypothesized that geosmin-degrading microorganisms on the GAC filters degrade
geosmin, thereby extending the GAC filter bed life.
In this study, the microbial communities growing in full-scale, biologically active GAC
filters at Saint Paul Regional Water Services were characterized using automated ribosomal
spacer analysis (ARISA) and high throughput DNA sequencing (Illumina sequencing) of 16S
rRNA gene fragments. This study showed that Saint Paul Regional Water Services has highly
diverse bacterial filter communities that are functionally stable throughout year. Illumina
sequencing revealed that a dominatnt bacterial phylum on the GAC filters was Nitrospira and that
pathogen levels (e.g., Enterobacteria) were negligible. Additionally, the effects of mediatype and inoculation on the development of a geosmindegrading
bacterial community on GAC filters was investigated using a pilot-scale column
system that was fed geosmin. A geosmin-degrading biofilm developed after 40 days of being
enriched with 100 ng/L of geosmin. Additionally, the geosmin-degrading organisms proved to be
robust in that they were able to resume geosmin degradation after 6 weeks when geosmin was
absent. The effects of GAC type and inoculation did not impact the biomass levels or geosmin removal.
University of Minnesota M.S. thesis. September 2012. Major: Civil Engineering. Advisors: Dr. Raymond Hozalski and Dr. Timothy LaPara. 1 computer file (PDF); vii, 98 pages, appendices A-G.
Hope Wilkinson, Katheryn Rachel.
Investigation of biologically active granular activated carbon filters..
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