Pathogens in WSP
Kara L. Nelson
Civil and Environmental EngineeringUniversity of California, Berkeley, USA
8th IWA Specialist Group Conference on Waste Stabilization PondsBelo Horizonte, Brazil, 26-30 April 2009
Pathogens in water (The bad guys)
Viruses: Hepatitis A, Rotavirus, Norovirus, Poliovirus
Bacteria: Vibrio cholera, Salmonella, Shigella, Campylobacter
Protozoa: Cryptosporidium, Giardia, Entamoeba
Helminths: Ascaris, Taenia, Trichuris, Hymenolepis
Pathogens in water (The bad guys)
Viruses: Hepatitis A, Rotavirus, Norovirus, Poliovirus
Bacteria: Vibrio cholera, Salmonella, Shigella, Campylobacter
Protozoa: Cryptosporidium, Giardia, Entamoeba
Helminths: Ascaris, Taenia, Trichuris, Hymenolepis
20-100 nmNo lipid membrane 0.5 – 1 μm
“Respond” to environment
2 – 20 μmThick shell
20 - 100 μmVery thick shell
Pathogen challenges in WSP
Many removal mechanisms Wide range in behavior among pathogens
No single indicator organism adequately models all pathogens
Actual pathogens are difficult (or impossible) to measure
Pathogen challenges in WSP cont.
Risk is based on actual pathogens
Under-design may lead to unacceptable health risks
Over-design results in extra expense, land area
Poor design produces unsafe effluent and wastes resources
Benefits of improved understanding
Practical design recommendations
Predictive models More appreciation for how great WSP are at removing pathogens
More and Better WSP (healthy people, protected environment….)
Main Removal Mechanisms
Sedimentation ( Sludge) Helminth eggs Protozoan cysts Particle-associated bacteria and viruses
Sunlight-mediated inactivation Viruses Bacteria Protozoan cysts
Removal by Sedimentation
Helminth eggs
Ascaris eggs vs ~ 1 m/h (others are lower)
Design equation: 24.9 0.0085
100 1 0.41R e Ayres et al. (1992)
Removal by Sedimentation
Cryptosporidium and Giardia cysts
Vs ~ 2.5 cm/h (Robertson et al. 1999)
Particle association may be important
Design equation (Grimason et al. 1993)
Removal by Sedimentation
Viruses and Bacteria Only if attached to particles High concentrations in sludge
Hydraulic considerations
Avoid uneven sludge distribution Avoid short-circuiting Recommendations:
Use momentum in inlet jet to “propel” influent
Stub baffles to deflect inlet and protect outlet
--OR-- Deep pit (aka Oswald)
Long vs stub baffles
Shilton and Harrison (2003) “Guidelines for the hydraulic design of waste stabilization ponds”
Sludge Management
Pathogens are concentrated in the sludge!
Sludge accumulation can decrease treatment performance Decreased HRT Change hydraulics
Apparent inactivation of helminth eggs in sludge cores
1
10
100
1000
0 2 4 6 8 10 12 14
Estimated sludge age, yrs
Via
ble
eg
gs/
g T
S
Mexicaltzingo
Texcoco
Xalostoc
Expon.(Xalostoc)Expon.(Texcoco)Expon.(Mexicaltzingo)
Nelson et al. (2004)
Inactivation of indicator organisms
0
1
2
3
4
0 2 4 6 8 10 12 14
Estimated sludge age, yrs
Log
rem
oval
Somatic coliphageF+ coliphageFecal coliformFecal enterococci
0
1
2
3
4
0 1 2 3 4 5 6 7 8
Time, months
Log
rem
oval
Sludge cores
Batch test
Nelson et al. (2004)
First-order inactivation rate constants in WSP sludge
k, d-1
Organism Sludge cores
Batch test
Dialysis chambers
Ascaris eggs
Mexicaltzingo 0.0009
Texcoco 0.0007 0.0021
Xalostoc 0.0010
Indicator organisms (Xalostoc)
Somatic coliphage 0.0016 0.0074
F+ coliphage 0.016 0.037
Fecal coliform 0.13 0.16
Fecal enterococci 0.26 0.20
Nelson et al. (2004)
Implications
Survival times in sludge Ascaris – years Viruses – months to years Bacteria – weeks to months
Sludge (most likely) requires treatment upon removal
Sunlight inactivation mechanisms in WSP
Direct damage by UVB
O2 ROS
O2
ROS
Indirect damage by endogenous sensitizers
Indirect damage by exogenous sensitizers
Based on work by Tom Curtis, Rob Davies-Colley
Wavelength (nm)
270 370 470 570 670 770
Mea
sure
d Ir
radi
ance
(W
/m2 )
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
UVB280-320
UVA320-400
Visible400-700
Solar Spectrum
Pond water absorbs sunlight
Wavelength (nm)
270 370 470 570 670 770
Mea
sure
d Ir
radi
ance
(W
/m2 )
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Ab
sorb
ance
0.0
0.2
0.4
0.6
0.8
1.0
Irradiance (W/m2)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Dep
th (cm)
0
2
4
6
8
10
550 nm
290 nm
De
pth
(cm
)
Sunlight penetration in WSP
Sunlight inactivation mechanisms in WSP
Direct damage by UVB
O2 ROS
O2
ROS
Indirect damage by endogenous sensitizers
Indirect damage by exogenous sensitizers
Sunlight Mechanisms
Mechanism Viruses BacteriaWave-lengths
Water Quality Factors
Direct UVB Yes Yes UVB Clear water!
Endogenous sensitizers
No YesUVB, UVA
High DO
Exogenous sensitizers
Some (not F+ DNA phage)
Some (E. coli, fecal coliforms only at high pH)
UVB, UVA, PAR
Lots of algae or
humic acids, High pH*
*MS2 not sensitive to high pH
Sunlight Mechanisms
Mechanism Viruses BacteriaProto-zoan cysts
Helminth eggs
Direct UVBAdenovirus,Polioviru
sCrypto
Endogenous sensitizers
NACampylobacter, Salmonella
Exogenous sensitizers
Ponds
Norovirus, Poliovirus
, Enteroviru
s
Salmonella, Shigella, V. cholera,
Campylobacter
Crypto
Remove by sedimentation!
Sources: da Silva et al. (2008); Araki et al. (2001); Love and Nelson (In prep); Sinton et al. (2007); review by Davies-Colley in Shilton, Ed (2005)
Sunlight Mechanisms
Mechanism Viruses BacteriaProto-zoan cysts
Helminth eggs
Direct UVBAdenovirus,Polioviru
sCrypto
Endogenous sensitizers
NACampylobacter, Salmonella
Exogenous sensitizers
Ponds
Norovirus, Poliovirus
, Enteroviru
s
Salmonella, Shigella, V. cholera,
Campylobacter
Crypto
Remove by sedimentation!
Sources: da Silva et al. (2008); Araki et al. (2001); Love and Nelson (In prep); Sinton et al. (2007); review by Davies-Colley in Shilton, Ed (2005)
Need to fill these boxes!
Need more studies on pathogens!
Technology for measuring pathogens is in industrialized countries
Pathogens are in developing countries qPCR detection being developed here at UFMG
Challenges with sunlight research
Must separate hydraulics from kinetics
Field studies Sunlight varies Can’t separate variables
Laboratory Sunlight must mimic solar spectrum Lab bacteria do not represent field bacteria
VBNC
Design Recommendations for Maturation Ponds
Need lots of algae! (high pH, DO) ?? High-rate algal ponds
Hydraulics (VERY important!) Create PFR-like flow with baffles Several ponds in series Shallow (0.5 m?) Vertical mixing Outlet in photic zone
“Dark” inactivation mechanisms
Predation Ammonia (high pH) Algal toxins Stress: temperature, pH, other wastewater constituents
WSP and Wastewater Reuse
Don’t need nutrient removal for reuse in agriculture
Many farmers currently use untreated or partially treated wastewater
WSP can meet WHO guidelines