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Modified slow sand filtration is being successfully applied throughout North America to treat rawwater that would not normally be considered suitable for slow sand filtration. This technologyinvolves the combination of one or more unit processes with slow sand filtration. These unitprocesses may include pre-treatment ozonation, pre-treatment advanced oxidation, roughingfiltration, post-treatment limestone contact or post-treatment biologically-active carbon filtration.The advantages of modified slow sand, including the relatively low operations and maintenancerequirements, are of benefit to many small systems applications.The ability of modified slow sand filtration, and biological filtration in general, to deal with highlevels of natural organic matter (NOM) and emerging contaminants has been a topic of recent research. This paperpresents the results of analyses of several emerging contaminants from finished water producedby operating conventional and modified slow sand filtration plants, along with pilot scaleresearch studies conducted in the US northeast and in Ontario, Canada. A summary of availableinformation on the removal of emerging contaminants and pathogens using biological processestypical of slow sand filtration is also presented. The ability of biological filtration to effectivelytreat a wide range of parameters, particularly the more exotic compounds, while retaining apractical and sustainable operation for small systems is reviewed, with an emphasis on theeffective application of this technology. The pathogens examined include Aeromonas sp.,Cryptosporidium parvum and Giardia lamblia. Indicator microorganisms such as Bacillus sporesand MS2 bacteriophage were also studied. Emerging contaminants included in these studiesconsist of endocrine disrupting compounds such as bisphenol-A (BPA), pharmaceuticals and thecyanobacterial toxin microcystin-LR. A brief discussion of the capacity of biological filtration toreduce geosmin and 2-MIB with and without ozone application is also included. Includes 29 references, figure.

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Edition: Vol. - No. Published: 06/01/2007 Number of Pages: 42File Size: 1 file , 580 KB