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Transport of Viruses, Bacteria, and Protozoa in Groundwater. Joe Ryan Civil, Environmental, and Architectural Engineering Department University of Colorado, Boulder Environmental Engineering Seminar October 11, 2000. Acknowledgments. Students
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Transport of Viruses, Bacteria, and Protozoa in Groundwater Joe Ryan Civil, Environmental, and Architectural Engineering Department University of Colorado, Boulder Environmental Engineering Seminar October 11, 2000
Acknowledgments • Students • University of Colorado: Jon Loveland, Jeff Aronheim, Annie Pieper, Becky Ard, Robin Magelky, Jon Larson, Theresa Navigato, Yvonne Bogatsu • UCLA/Yale University: Jun Long, Ning Sun, Chun-han Ko • Collaborators • Ron Harvey, U.S. Geological Survey • Menachem Elimelech, Yale University • Funding • National Water Research Institute • U.S. Environmental Protection Agency • Laboratory Assistance • Chuck Gerba, University of Arizona • Joan Rose, University of South Florida • Field Assistance • Denis LeBlanc & Kathy Hess, U.S. Geological Survey
Public Health Problem • Waterborne Disease Outbreaks • estimates for the United States • 1 to 6 million illnesses per year • 1000 to 10,000 deaths per year • only 630 documented outbreaks 1971-1994 • Milwaukee, Wisconsin, 1993 • Cryptosporidium, the “hidden germ” • about 400,000 illnesses, greater than 100 deaths • DNA evidence: human, not bovine, origin
Public Health Problem • Waterborne Disease Outbreaks • acute gastrointestinal illness • short duration, “self-resolving” for most people • chronic, severe, fatal for some • infants and elderly • pregnant women • immuno-compromised • more serious illnesses • heart disease, meningitis, diabetes (coxsackie virus) • liver damage, death (hepatitus virus)
Public Health Problem • Microbial Perpetrators • viruses • bacteria • protozoa • Where are they coming from? • groundwater (58%), surface water • point source, non-point source
Viruses • Enteric • replicate only in gut • Size • 20 – 200 nm • Structure • protein capsid • RNA or DNA
Viruses • Life Cycle • ingestion • drinking water • within the gut • adsorption • penetration • transcription • replication • assembly • host cell lysis • excretion from gut
Bacteria • Enteric • grow in gut (only?) • Size • 0.5 to 2 m • Structure • cell walls • proteins • phospholipids, fatty acids • motililty • flagellae • cilia
Bacteria • Life Cycle • ingestion • meat, vegetables, drinking water • within the gut • adsorption • penetration • growth • release of toxins • excretion from gut Vibrio Cholera adhering to rabbit villus E. coli adhering to calf villus
Protozoa • Enteric • grow in gut only • Size • 3 to 12 m • Cyst Structure • rugged protective membrane • carries trophozoites
Protozoa • Life Cycle • ingestion • drinking water • within the gut • excystation • parasitic growth • cyst formation • excretion from gut
Occurrence in Groundwater • Viruses • 38% positive by PCR • 7% positive by cell culture • Bacteria • 40% positive for coliform bacteria • 50-70% positive for enterococci • Protozoa • 12% Giardia and/or Cryptosporidium(5% in vertical wells)
Monitoring in Groundwater • Maximum Contaminant Level • coliform bacteria – 40 per liter • viruses – 2 per 107 L (proposed, GWDR) • Ground Water Disinfection Rule • will require disinfection unless “proof” of adequate “natural disinfection” • viruses nominated as target microbe • Virus Transport Models • predictions of travel time • attachment and inactivation
Microbe Transport • Transport equation dispersion advection equilibrium attachment/ release kinetic attachment/ release growth or inactivation/ “die-off”
Microbe Attachment • Attachment • kinetic • colloid filtration • collision frequency • collision efficiency • release • first-order (kdet) • much slower than attachment • equilibrium • distribution coefficient • linear, reversible tracer concentration microbe time tracer concentration microbe time
Microbe Attachment • Surface Chemistry • capsids, cell walls • carboxyl – RCOO- • amine – RNH3+ • net surface charge • usually negative • pHpzc ~3-4 • for viruses, pHpzc can be estimated from protein content of capsid
Microbe Attachment • Porous Media Surface Chemistry • negative • quartz, feldspars, etc. • clay faces • positive • iron, aluminum oxides • clay edges • electrostatic interactions • favorable deposition sites • unfavorable deposition sites
Microbe Attachment • Microbe Size • small • collisions caused by Brownian motion • large • collisions caused by settling • Microbe Density • Range 1.01 to 1.05 g cm-3 • collisions caused by settling
Microbe Attachment • Optimal Size for Transport • about 1-2 m • bacteria • viruses collide by diffusion • protozoa collide by settling • protozoa also removed by straining
Microbe Attachment • Target Organism • collision efficiency • about the same for all microbes • variation in comes from porous media • collision frequency • favors bacteria • BACTERIA, but… • adhesion favored for growth • biofilms
Virus Attachment • Bacteriophage PRD1 • Cape Cod field experiments • sewage-contaminated zone • uncontaminated zone • 100 L injections • multi-level samplers
Virus Attachment • Transport favored in contaminated zone • PRD1 attachment sites blocked by sewage organic matter • collision efficiency fraction of favorable deposition sites
Microbe Growth/Inactivation • Growth • viruses – no replication outside gut • bacteria – growth possible, but unlikely • protozoa – no growth outside gut
Microbe Growth/Inactivation • Inactivation • viruses – mainly temperature-dependent • bacteria – lysis? predation? • protozoa – generally resistant to disinfection, so inactivation is slow?
Virus Inactivation • Viruses • inactivation in solution • first-order decay • inactivation on surfaces? • effect of strong attachment forces
Virus Inactivation • Bacteriophage MS2 • Cape Cod sediment • 32P DNA • 35S protein capsid • rapid loss of infectivity • release of radiolabels
Summary • Predicting microbe transport • less difficult for viruses, protozoa cysts • no growth, inactivation simpler • more difficult for bacteria • motility • adhesion behavior motivated by growth, nutrients • growth, die-off more complicated • Bacteria should be target organism (?) • least frequent collisions, motility • may be complicated by longer-term adhesion strategies