1. How persistent are pathogens in the environment?
3.3 Pathogen reduction
collection
Agricultural
use
treatment
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

2. 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 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 2

3. Times given in days if not otherwise stated
Estimated survival times for microorganisms in faeces, sludge, soil and on crop
Times given in days if not otherwise stated
(Faechema 1983 and Kowanb 1985, in EPA 1999) 3

4. Inactivation of microorganisms in faeces
Inactivation of microorganisms in faeces
Organism to be modelled
4°C/low temp range
20°C/high temp range
E.coli*
T90 = days
T90 = days
Enterococci*
T90 = days
Same as 4°C
Bacteriophages
T90 = days
T90 = days
Salmonella*
T90 = days
EHEC*
T90 = days
Rotavirus
conservative model – no reduction T90 = days
T90 = days
Giardia
T90 = days
T90 = 5-50 days
Cryptosporidium
T90 = days
T90 = days
Ascaris
T90 = days
T90 = days
*Possible growth not taken into consideration
(Arnbjerg-Nielsen et al., 2005) 4

5. 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 4°C, T90 = ~ 1-2 months at 20°C)
Factors that speed up die-off
elevated pH ( , urea ammonia)
higher temperature
lower dilution
Time (days)
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden

6. Parameters affecting microbial survival in the environment
Temperature
Low temperature prolongs survival. Inactivation if >40°C, treatment processes 55-65°C. 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 6

7. Barriers required to prevent the spread of pathogens
(Esrey et al. 1998) 7

8. 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 8

9. Expected removal (log10) of micro- organisms by wastewater treatment barrier
Process
Bacteria
Helminths
Viruses
Cysts
Primary sedimentation Plain Chemically assisted
Activated sludge
0-2
0-1
Bio filtration
Aerated lagoon
1-2
1-3
Oxidation ditch
Disinfection
2-6
0-4
0-3
Waste stabilization ponds
1-6
1-4
Effluent storage reservoirs
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 11

12. 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

15. 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 ( ), high temperature (31-37°C) and low moisture level (24-55%)
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden

16. Reduction of Salmonella typhimurium phage 28B
in 12 latrines over time for different measures
                                                                                                                                                                                                          
Carlander & Westrell, 1999

17. Reduction of Ascaris suum eggs
                                                                                                                                                                                                          
(Carlander & Westrell 1999)

18. Inactivation of Giardia and Ascaris on coriander leaves
Inactivation on crops
Inactivation of Giardia and Ascaris on coriander leaves
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden

19. Closing the nutrient loop in a safe way
collection
agricultural use
treatment
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden 19

20. 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/realistic measures)
Insignificant amounts of pathogens
No additional individuals inflicted by disease
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden 20

21. Wastewater effluent Sludge
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

22. Treatment of faeces Storage Biological methods Chemical treatment
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