Constructed Wetlands and Pathogens

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Constructed Wetlands and Pathogens

• By Stephanie Boone

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Background

• The cleanest oceans have 1.1x1029 prokaryotic
  cells and 7.5x107 viruses per teaspoon.
• Riverine wetland estimated plantonic viruses
  3.8x105 and surface viruses 1.3x107 per ml.

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Background

• 2001 265 of deaths worldwide were caused by
  infectious disease.
• Water-related diseases are leading cause of
  morbidity and mortality.
• In the US between 1971 and 1994 there were 650
  waterborne outbreaks and 569,754 cases of
  waterborne illness.

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Background

• Pathogens enter the groundwater supply through
• Sewage treatment effluents Excretion of 1011
  viral particles per gram of feces.
• Onsite septic waste treatment discharges traced
  viruses travel 328 ft. through groundwater
• Leachates from sanitary landfills
• Land runoff from urban, agricultural and natural
  areas.
• 58 waterborne outbreaks connected with
  groundwater.
• 33 associated with surface water.

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Background
Microorganisms known for disease transmission by
water include Giardia, Cryptosporidium,
Legionella, E. Coli 0157 H7, rotavirus, hepatitis
E, norovirus, Hepatitis A, poliovirus,
adenovirus, astroviruses.
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Constructed Wetland Removal of Pathogens

• Wetlands remove pathogens through a combination
  of
• Sedimentation
• Precipitation
• Absorption to soil particles
• Assimilation by plant tissue
• Microbial transformation

• Studies indicate that pathogen removal can be
  effected by
• Turbidity
• Temperature
• The presence of vegetation
• Wetland type (subsurface or surface)

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Constructed Wetland Studies

• Turbidity
• Higher turbidity decreases viral removal and
  increases parasite removal.
• Blocks UV light.
• Temperature
• Increase temperature increases viral removal.
• Varies depending on parasite.

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Constructed Wetland Studies

• Vegetation
• Increase in vegetation density leads to increase
  in viral removal.
• Effect on parasite removal ???.
• Dense vegetation facilitates sedimentation,
  sorption straining and other decay process.
• Plants can damage enteric pathogens by excreting
  toxic antimicrobial substances from roots.

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Type of Wetland

• Subsurface flow removed 95 of coliphage and 99
  of Polio virus as compared with 40 removal in a
  duckweed pond.
• Duckweed pond removed 89 - 98 of Giardia and
  Cryptosporidium as compared to 58-73 in a
  surface wetland.

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Conclusions

• Generally factors that decrease heat and UV light
  have a negative effect on pathogenic virus
  removal.
• Parasites are generally removed by sedimentation
  and removal factors vary depending on parasite.
• Combination of filtration or removal sources are
  best to insure maximum pathogen removal.

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References Available upon Request