title: Investigation of E. coli and Virus Reductions Using Replicate, Bench-Scale Biosand Filter Columns and Two Filter Media.
abstract: The biosand filter (BSF) is an intermittently operated, household-scale slow sand filter for which little data are available on the effect of sand composition on treatment performance. Therefore, bench-scale columns were prepared according to the then-current (2006-2007) guidance on BSF design and run in parallel to conduct two microbial challenge experiments of eight-week duration. Triplicate columns were loaded with Accusand silica or crushed granite to compare virus and E. coli reduction performance. Bench-scale experiments provided confirmation that increased schmutzdecke growth, as indicated by decline in filtration rate, is the primary factor causing increased E. coli reductions of up to 5-log10. However, reductions of challenge viruses improved only modestly with increased schmutzdecke growth. Filter media type (Accusand silica vs. crushed granite) did not influence reduction of E. coli bacteria. The granite media without backwashing yielded superior virus reductions when compared to Accusand. However, for columns in which the granite media was first backwashed (to yield a more consistent distribution of grains and remove the finest size fraction), virus reductions were not significantly greater than in columns with Accusand media. It was postulated that a decline in surface area with backwashing decreased the sites and surface area available for virus sorption and/or biofilm growth and thus decreased the extent of virus reduction. Additionally, backwashing caused preferential flow paths and deviation from plug flow; backwashing is not part of standard BSF field preparation and is not recommended for BSF column studies. Overall, virus reductions were modest and did not meet the 5- or 3-log10 World Health Organization performance targets.
authors: Department of Civil, Construction and Environmental Engineering, University of Alabama, Tuscaloosa, AL 35487, USA. cstauber@gsu.edu.
authors: Mark
authors: M
authors: Elliott
authors: School of Public Health, Georgia State University, Atlanta, GA 30302, USA. cstauber@gsu.edu.
authors: Christine E
authors: CE
authors: Stauber
authors: Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC 27599, USA. fran_digiano@unc.edu.
authors: Francis A
authors: FA
authors: DiGiano
authors: Hubert Department of Global Health, Rollins School of Public Health, Emory University, Atlanta, GA 30322, USA. anna.aceituno@emory.edu.
authors: Anna Fabiszewski
authors: AF
authors: de Aceituno
authors: Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC 27599, USA. mark_sobsey@unc.edu.
authors: Mark D
authors: MD
authors: Sobsey
mesh_terms: D025622:Bacteriophage PRD1 / Q000302:isolation & purification; D029822:Enterovirus B, Human / Q000302:isolation & purification*; D004926:Escherichia coli / Q000302:isolation & purification*; D005374:Filtration / Q000295:instrumentation* / Q000379:methods; D017909:Levivirus / Q000302:isolation & purification; D012822:Silicon Dioxide; D014871:Water Microbiology; D018508:Water Purification / Q000295:instrumentation* / Q000379:methods
chemical_list: C007886:granite; D012822:Silicon Dioxide
keywords: household water treatment and safe storage (HWTS); intermittent; point-of-use (POU); slow sand filter