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….)

We already know a lot!

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

12

Sludge distribution in Xalostoc

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

Back to Big Picture

Complicated science ≠ Complicated solutions

Some treatment is better than no treatment

Current design approaches work

Attention to hydraulics!

Sludge management!