Sustainable Sanitation for the 21st Century

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3.3 Pathogen reduction
How persistent are pathogens in the
environment? How can we prevent exposure and
disease transmission in sanitation systems?

• Learning objective to become familiar with
• the behaviour of pathogens in the environment
• the effects of treatment
• strategies for minimizing the transmission of
  disease, especially in relation to agricultural
  use of excreta

Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
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Transmission of infectious disease during reuse

• Mexico untreated wastewater gives 33 higher
  risk of diarrhoeal diseases (Cifuentes et al.
  1998)
• Israel (kibbutz) partially treated stabilization
  pond effluent gives two-fold excess risk of
  enteric disease in 0-4 year-old age group
  (Fattal et al. 1986)
• No recorded incidents associated with
  appropriately treated wastewater (Cooper
  Olivieri 1998)
• National Research Council (NRC, USA, 2000)
  evaluated 23 studies no proof for elevated or
  decreased risk when reusing sewage sludge
• Risk assessment a valuable tool

Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
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Times given in days if not otherwise stated
Estimated survival times for microorganisms in
faeces, sludge, soil and on crop
(Faechema 1983 and Kowanb 1985, in EPA 1999)
4
 
Inactivation of microorganisms in faeces
Possible growth not taken into consideration
(Arnbjerg-Nielsen et al., 2005)
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Survival of microorganisms in human urine

• Organism group (ex.) Survival time
• Bacteria (Salmonella, E. coli) - Short (T90
  days)
• Protozoa (Cryptosporidium) - Average (T90 1
  month)
• Virus (rotavirus, bacteriophage) - Long (no
  reduction at 4C, T90 1-2 months at
  20C)
• Factors that speed up die-off
• elevated pH (7 9, urea ammonia)
• higher temperature
• lower dilution

Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
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Parameters affecting microbial survival in the
environment
Temperature Low temperature prolongs survival. Inactivation if gt40C, treatment processes 55-65C.
pH Neutral pH (7) suits organisms and their survival. Inactivation requires highly acidic or alkaline conditions.
Moisture Moisture (e.g. in soil) favours the survival.Inactivation if drying condition.
Solar radiation/UV-light Inactivation by natural solar radiation or UV-lamps.
Other microorganisms Pathogens survive longer in sterile water. Inactivation through competition and by predation.
Ammonia Often affects microorganisms negatively. Inactivation by ammonia produced at high pH.
Nutrients Needed for growth of bacteria. Inactivation by lack of nutrients.
Other factors Oxygen availability, chemical compounds.
Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
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Barriers required to prevent the spread of
pathogens
(Esrey et al. 1998)
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How can we kill pathogens?

• We cannot only wait for the pathogens to be
  inactivated (eventual pathogen die-off)
• Measures can be taken to introduce conditions
  that are hostile to pathogen survival, such as
• High temperature,
• Low moisture,
• Competing microflora,
• High or low pH
• Ammonia gas
• etc.

But, difficult to establish T90 for reduction of
each and every pathogen
Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
9
Expected removal (log10) of micro-organisms by
wastewater treatment barrier
Process Bacteria Helminths Viruses Cysts
Primary sedimentation Plain Chemically assisted 0-11-2 0-21-3 0-10-1 0-10-1
Activated sludge 0-2 0-2 0-1 0-1
Bio filtration 0-2 0-2 0-1 0-1
Aerated lagoon 1-2 1-3 1-2 0-1
Oxidation ditch 1-2 0-2 1-2 0-1
Disinfection 2-6 0-1 0-4 0-3
Waste stabilization ponds 1-6 1-3 1-4 1-4
Effluent storage reservoirs 1-6 1-3 1-4 1-4
Large variations depend on organism and difficult
to predict
Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
10
Greywater treatment

• Treatment to remove grease, N, P, chemicals.and
  pathogens (see chapter 4)
• Choice of treatment method is dependent on the
  intended use
• Specific risks of use
• Irrigation, subsurface
• Treatment in ponds limit exposure
• Infiltration, drinking water
• Handling to avoid smell

Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
11
Barriers to pathogens in sludge handling
Source-separation
Wastewater treatment
Sludge treatment
Restrictions on usage
Faeces Urine Greywater Stormwater Industry
Sludge (Treated wastewater)
Treated sludge
Sludge application
Wastewater
Control/Regulations
Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
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Urine diversion in dry sanitation systems

• Will result in (compared to mixing of faeces and
  urine)
• Less smell
• Less volume (slower filling up, less to handle)
• Prevention of dispersal of pathogen-containing
  material (spilling, leaching)
• Safer and easier handling and use of excreta
  (volume, treatment) Less risk for disease
  transmission
• Urine diversion is therefore recommended

Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
13
Treatment of faeces as barrier

• Primary treatment in dry toilet
• Adding drying material reduces pathogen load
• Storage
• Ambient conditions
• Biological methods
• Composting (heat, microbial competition,
  pH-changes)
• Anaerobic digestion (competition, pH-changes)
• Chemical treatment
• Alkaline treatment
• Ash, lime (pH-elevation and desiccation)
• Urea (ammonia)
• Incineration

Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
14
Storage of urine as a barrier

• The most appropriate treatment method
• Other methods tried out in order to reduce the
  volume
• Easier handling for agricultural use
• Storage with low air exchange (tight containers)
  best method to keep the nutrients in urine
• Only necessary in large-scale systems
• Existing guidelines in module 3.4

Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
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Survival study double-vault latrines in Vietnam

• Design of study
• Ascaris and bacterio-phage (mimicks virus) added
  to the vault material
• Study the effect of changes in pH, temperature
  and moisture content
• 12 double-vault latrines were studied(of
  different design)
• (Carlander Westrell
  1999)

Results A total inactivation within 6 months of
Ascaris and the model virus (bacteriophage) pH
played a significant role for the inactivation of
the bacterio-phages in the faecal material The
inactivation of bacterio-phages and Ascaris was
achieved through a combination of high pH
(8.5-10.3), high temperature (31-37C) and low
moisture level (24-55)
Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
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Reduction of Salmonella typhimurium phage 28B in
12 latrines over time for different measures
                                              
                                                  
                                                  
                                                  
      
Carlander Westrell, 1999
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Reduction of Ascaris suum eggs
                                               
                                                  
                                                  
                                                  
     
(Carlander Westrell 1999)
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Inactivation on crops
Inactivation of Giardia and Ascaris on coriander
leaves
Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
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Closing the nutrient loop in a safe way
Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
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Treatment as a barrier
Treatment as a barrier A combination of barriers
to decrease exposure of humans to excreta should
be applied in order to reduce risks for disease
transmission in ecological sanitation systems.
Treatment of the excreta is considered as a
necessary step for the subsequent use as
fertiliser on (agricultural) land.
(EcoSanRes, 2004)

• The goal is to significantly reduce risks zero
  risk is not possible
• Minimise risks (considering viable/practical/rea
  listic measures)
• Insignificant amounts of pathogens
• No additional individuals inflicted by disease

Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
21
Wastewater treatment

• Treatment steps - barriers
• Microorganisms reduced by 70-99,99 in STP
  (Sweden)
• Treatment plants not optimised for pathogen
  removal
• Generally, no regulations on outgoing (treated)
  wastewater
• Disinfection is an efficient method, but causes
  other problems
• Sewage sludge has high concentration of pathogens

Incoming wastewater Wastewater effluent
Sludge
Faeces
Dilution
Reduction, die-off
Concentration
Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden
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Treatment of faeces

• Storage
• Ambient conditions
• Biological methods
• Composting (heat, microbial competition,
  pH-changes)
• Anaerobic digestion (heat, microbial competition,
  pH-changes)
• Chemical treatment
• Alkaline treatment
• Ash, lime (pH-elevation and desiccation)
• Urea (ammonia)
• Incineration

Caroline Schönning, Swedish Institute for
Communicable Disease Control, Solna, Sweden