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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
3.3 Pathogen reduction
How persistent are pathogens
in the environment?
How can we prevent
exposure and disease
transmission in sanitation
systems?
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
collection
Agricultural use
treatment
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
Transmission of infectious disease during reuse
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
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)
Organism to be modelled 4°C/low temp range 20°C/high temp range
E.coli* T90 = 70-100 days T90 = 15-35 days
Enterococci* T90 = 100-200 days Same as 4°C
Bacteriophages T90 = 20-200 days T90 = 10-100 days
Salmonella* T90 = 10-50 days
EHEC* T90 = 10-30 days Same as 4°C
Rotavirus conservative model – no reductionT90 = 100-300 days
T90 = 20-100 days
Giardia T90 = 15-100 days T90 = 5-50 days
Cryptosporidium T90 = 30-200 days T90 = 20-120 days
Ascaris T90 = 100-400 days T90 = 50-200 days
*Possible growth not taken into consideration
Inactivation of microorganisms in faeces
(Arnbjerg-Nielsen et al., 2005)
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 (7 9, urea ammonia)
• higher temperature
• lower dilution
Survival of microorganisms in human urine
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
1E+5
1E+6
1E+7
1E+8
1E+9
0 50 100 150 200Tid [dagar]
4C20C
Time (days)
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.
Parameters affecting microbial survival in the environment
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
(Esrey et al. 1998)
Barriers required to prevent the spread of 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
How can we kill pathogens?
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
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, difficult to predict
Expected removal (log10) of micro-organisms by wastewater treatment barrier
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
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
Faeces
Urine
Greywater
Stormwater
Industry
WastewaterSludge
(Treated wastewater)
Treated sludge
Source-separation
Wastewater treatment
Sludge treatment
Restrictions on usage
Control/Regulations
Sludge application
Barriers to pathogens in sludge handling
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
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
Urine diversion in dry sanitation systems
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
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
Treatment of faeces as barrier
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
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
Storage of urine
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
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)
Survival study – double-vault latrines in Vietnam
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Results:
A total inactivation of Ascaris and the model virus
(bacteriophage) was achieved within 6 months
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 (31-37°C) and low moisture level (24-55%)
Reduction of Salmonella typhimurium phage 28Bin 12 latrines over time for different measures
Carlander & Westrell, 1999
Reduction of Ascaris suum eggs
(Carlander & Westrell 1999)
Inactivation of Giardia and Ascaris on coriander leaves
Inactivation on crops
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
collection
agricultural use
treatment
Closing the nutrient loop in a safe way
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
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.
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 diseased
Treatment as a barrier
(EcoSanRes, 2004)
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Incoming wastewater
Wastewater effluent Sludge
Reduction, die-off
Concentration
Dilution
Wastewater treatment as a barrier
Faeces
Treatment steps = barriers
Microorganisms reduced by 70-99,99% in STP (in Sweden)
Treatment not optimised for pathogen removal
Generally no regulations on outgoing (treated) wastewater
Disinfection efficient method, but causes other problems
Limiting exposure from outlet is important
Sewage sludge – concentration of pathogens
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Primary treatment In the toilet (on-site) Some reduction of pathogens Reduce risks in subsequent handling
Secondary treatment After finished collection
• Off-site or on-site (scale dependent)
Significant reduction of pathogens Rendering the material ”safe” to use as fertiliser/soil
improver Possibilities will be dependent on primary treatment
Treatment of faeces
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
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
Treatment of faeces (continued)
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
A total inactivation of Ascaris and the model virus (bacteriophage) was achieved within 6 months
pH played a significant role in the inactivation of the bacteriophage in the faecal material
The inactivation of the bacteriophage and Ascaris was achieved through a combination of high pH (8.5-10.3), high temperature (31-37°C) and low moisture (24-55%)
Conclusions from the Vietnam study
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
To prevent or decrease disease transmission Reduce number of pathogens Hinder actual exposure to the pathogen-containing
material
In analogy with different steps in e.g. drinking water treatment
Health protection measures (WHO terminology) Technical, behavioural, medical, etc.
Barriers of transmission
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Eventual pathogen die-off outside the body Persistence varies depending on type Bacteria may grow in the environment Helminth eggs have a latency period before they become
infectious Natural conditions will affect rate of inactivation
temperature, moisture, competing microflora, etc. Alter the conditions to increase the die-off rate
temperature, pH, moisture, etc.
But, difficult to state exact time-parameter limits for elimination of each and every pathogen
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
How can we kill pathogens?