Browsing by Subject "Geosmin"
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Item Effect of lime solids and natural organic matter on geosmin removal via powdered activated carbon.(2012-09) Rescorla, AndrewMinneapolis Water Works, a 60 million gallon per day water treatment facility, experiences seasonal taste and odor episodes that result in customer complaints. Geosmin, which imparts an earthy or musty odor, is one taste and odor causing compound that has been detected at levels exceeding its odor threshold concentration. Powdered activated carbon (PAC) is added in the lime softening plant to remove geosmin via sorption. It is important to understand how lime solids, contact time, and natural organic matter (NOM) affect PAC performance so that the correct PAC dose and application point are used in order to maximize geosmin removal and minimize PAC cost. Results from jar test experiments suggest that lime and alum do not inhibit the sorption of geosmin when added simultaneously with PAC but that contact time is the most important parameter. Therefore, PAC should generally be added to the water at the point which maximizes contact time. Conversely, PAC contained in settled lime solids exhibited a reduced sorption capacity compared to fresh PAC, indicating that PAC contained in recycled lime solids has minimal impact on geosmin removal at the full-scale treatment plant. Additionally, the impact of NOM on PAC performance was investigated. Using Suwanee River (SR) NOM, an increase in 1 mg/L dissolved organic carbon resulted in a decrease in geosmin removal efficiency of 2.7% (at a PAC dose of 7.5 mg/L). Suwanee River humic acid, SR fulvic acid, and Pony Lake fulvic acid also inhibited geosmin sorption, but the effect was significantly lower. For the three SR NOM types, the inhibitive effective increased as average molecular weight of the NOM decreased. Data from the full-scale plant were in reasonable agreement with laboratory jar test data for PAC added immediately before or after lime. For PAC added at the recarbonation tanks, geosmin removal efficiencies were much higher at the full-scale plant than in the jar test experiments. This could be due to the small sample size (n=4) of the full-scale data set or differences in DOC levels between jar tests and the full-scale plant.Item Investigation of biologically active granular activated carbon filters.(2012-09) Hope Wilkinson, Katheryn RachelGeosmin 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.