On Site Sewage Facility Pathogen Removal

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On Site Sewage FacilityPathogen Removal
Disinfection Alternatives

• Stephanie L Sturman, R. S., D. R., S. E.
• Senior Inspector,
• Watershed Protection Group,
• Harris County Public Infrastructure Department

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What is the purpose of disinfecting wastewater?

• To destroy, de-activate or reduce to an
  acceptable level, remaining pathogenic organisms
  in wastewater to prevent the transmission of
  infection, illness or disease.

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What is a pathogenic organism?

• An infectious agent or organism that causes or is
  capable of causing a disease.

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Pathogen Survival

• Even after proper treatment processes have
  occurred, pathogens can survive for days in the
  external environment, and most notably, on plant
  life, (your fruit vegetable gardens)!

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Pathogen Survival (cont.)

• Transmission of the pathogen, whether directly
  or not, is most commonly through ingestion.
• The following pathogens are known to be
  transmitted by the fecal to oral route.

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Common Pathogenic Bacteria in Wastewater

• Salmonella
• Typhoid Fever (general pain, fever, intestinal
  bleeding) Foodborne Illness
• Shigella
• Shigellosis (Fever, Diarrhea usually bloody
• Stomach Cramps.)
• E. Coli (also, an indicator bacterium)
• Only a few strains cause infection
• Diarrhea, fever, abdominal cramps

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Most Recent Bacterial Outbreak?

• 1. Listeria on Cantalopes
• 2. Salmonella on Spinach

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Common Pathogenic Viruses in Wastewater

• Rotovirus (stable in the environment)
• Fever, Vomiting, Diarrhea, Dehydration
• Hepatitus A (highly contagious)
• Fatigue, Nausea, Loss of appetite, Jaundice
• Norwalk Virus
• Vomiting, Diarrhea, Low-grade fever
• (photo courtesy of the EPA)

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Common Pathogenic Protozoa in Wastewater

• Giardia Lambia
• Nausea, Bloating, Diarrhea, Anorexia
• Entamoeba histolytica
• Colitis, Dysentery, Diarrhea, Liver abscess
• Cryptosporidium parvum
• Mild to Chronic Diarrhea

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So now we know what some of the bugs in our
wastewater are, how do we eliminate pathogens in
wastewater?
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Pathogen removal/ disinfection

• First Primary Treatment (settling and
  entrapment)
• - Is septic tank large enough to handle the
  organic load and to trap most pathogens in the
  sludge or scum layer?
• -Is it sized to prevent too much carryover?
• - Better effluent Better Disinfection

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Pathogen removal/ disinfection (cont.)

• Second Secondary Treatment
• (Aerobic Treatment Systems, Filter Media Systems)
• Secondary treatment can remove up to 90 of
  organics and solids
• Is the Treatment Unit sized properly?
• Is it functioning properly?

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Pathogen removal/ disinfection (cont.)

• Third Disposal or Disinfection disposal
• In subsoil disposal, disinfection occurs in the
  soil itself
• In surface disposal, we need to disinfect the
  waste water further.

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Assuming the system is sized and functioning
well, what types of disinfection are available to
the On Site Septic System owner?

• Chlorination
• Ultraviolet Light
• Ozone

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Chlorination

• Tablet Liquid Chlorination
• The appropriate chlorine for disinfecting
  wastewater is either Calcium Hypochlorite or
  Sodium Hypochlorite. When diluted with the
  wastewater, Hypochlorous Acid is formed, which
  actually attacks the pathogens.
• Chlorine disinfects by attacking the pathogens
  cell wall interior structures, causing
  oxidation and death.
• Very common disinfectant/ (disinfectant of
  choice).
• Easy to use and monitor/measure
• More effective on bacteria than on viruses or
  protozoa
• May leave a chemical residue in the environment.

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Examples of chlorinators
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Ultraviolet Light

• Ultraviolet Light kill pathogens by sending
  electromagnetic energy from the lamp to the
  cells genetic material, which kills or prevents
  cell reproduction.
• More effective at pathogenic virus and protozoa
  removal than chlorination.
• No chemical residue in the environment.
• The intensity of the light is important for
  proper disinfection (250 nm-270 nm is considered
  the optimal range)

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Ultraviolet Light (cont.)

1. Very important to have a fairly clear effluent so
   the UV light can penetrate all pathogens passing
   through.
2. Requires knowledge in installation, regular
   maintenance, and cleaning.
3. Bulbs need to be changes about once a year.

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Examples of UV Devices
Not really for Septic systems, but the effect is
similar- ZAP!
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Ozone

• Utilizes pure oxygen or pure air and a high
  voltage electrical discharge to produce Ozone.
• The Ozone is fed into a contact chamber with the
  wastewater.
• Ozone disinfects basically by oxidizing the cell
  wall, damage to interior cell components,
  rendering them harmless.

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Ozone

• Increases dissolved oxygen in effluent and any
  receiving streams.
• More effective than UV Chlorine against virus,
  bacteria and protozoa.
• Any off-gases have to either recycled or
  destroyed.
• Ozonation is not as readily available as other
  technologies, as it fairly complex, expensive and
  can be dangerous for improperly trained persons
  working on these systems.

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Conclusion

• It seems that the disinfection methods that work
  best are also the most complicated.
• There is not a single method of disinfection that
  is 100 perfect for all systems.
• The designer, installer, maintenance provider and
  property owner need to work together to determine
  the most economic and effective method of
  disinfection for the On- Site Sewage Facility.