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Pathogens in WSP. Kara L. Nelson Civil and Environmental Engineering University of California, Berkeley, USA. 8th IWA Specialist Group Conference on Waste Stabilization Ponds Belo Horizonte, Brazil, 26-30 April 2009. Pathogens in water (The bad guys).

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pathogens in wsp

Pathogens in WSP

Kara L. Nelson

Civil and Environmental Engineering

University of California, Berkeley, USA

8th IWA Specialist Group Conference on Waste Stabilization Ponds

Belo Horizonte, Brazil, 26-30 April 2009

pathogens in water the bad guys
Pathogens in water (The bad guys)

Bacteria: Vibrio cholera, Salmonella, Shigella, Campylobacter

Viruses: Hepatitis A, Rotavirus, Norovirus, Poliovirus

Protozoa: Cryptosporidium, Giardia, Entamoeba

Helminths: Ascaris, Taenia, Trichuris, Hymenolepis

pathogens in water the bad guys1
Pathogens in water (The bad guys)

20-100 nm

No lipid membrane

0.5 – 1 μm

“Respond” to environment

Bacteria: Vibrio cholera, Salmonella, Shigella, Campylobacter

Viruses: Hepatitis A, Rotavirus, Norovirus, Poliovirus

20 - 100 μm

Very thick shell

2 – 20 μm

Thick shell

Protozoa: Cryptosporidium, Giardia, Entamoeba

Helminths: Ascaris, Taenia, Trichuris, Hymenolepis

pathogen challenges in wsp
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
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
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
Main Removal Mechanisms
  • Sedimentation ( Sludge)
    • Helminth eggs
    • Protozoan cysts
    • Particle-associated bacteria and viruses
  • Sunlight-mediated inactivation
    • Viruses
    • Bacteria
    • Protozoan cysts
removal by sedimentation
Removal by Sedimentation

Helminth eggs

  • Ascaris eggs vs ~ 1 m/h (others are lower)
  • Design equation:

Ayres et al. (1992)

removal by sedimentation1
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 sedimentation2
Removal by Sedimentation
  • Viruses and Bacteria
    • Only if attached to particles
    • High concentrations in sludge
hydraulic considerations
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
Long vs stub baffles

Shilton and Harrison (2003) “Guidelines for the hydraulic design of waste stabilization ponds”

sludge management
Sludge Management
  • Pathogens are concentrated in the sludge!
  • Sludge accumulation can decrease treatment performance
    • Decreased HRT
    • Change hydraulics
inactivation of indicator organisms
Inactivation of indicator organisms

Sludge cores

Batch test

Nelson et al. (2004)

implications
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

ROS

O2

Sunlight inactivation mechanisms in WSP

Direct damage by UVB

O2

ROS

Indirect damage by endogenous sensitizers

Indirect damage by exogenous sensitizers

Based on work by Tom Curtis, Rob Davies-Colley

solar spectrum
Solar Spectrum

UVB

280-320

UVA

320-400

Visible

400-700

sunlight penetration in wsp
Sunlight penetration in WSP

290 nm

550 nm

Depth (cm)

sunlight inactivation mechanisms in wsp1

ROS

O2

Sunlight inactivation mechanisms in WSP

Direct damage by UVB

O2

ROS

Indirect damage by endogenous sensitizers

Indirect damage by exogenous sensitizers

sunlight mechanisms
Sunlight Mechanisms

*MS2 not sensitive to high pH

sunlight mechanisms1
Sunlight Mechanisms

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 mechanisms2
Sunlight Mechanisms

Remove by sedimentation!

Need to fill these boxes!

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 more studies on pathogens
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
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
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
“Dark” inactivation mechanisms
  • Predation
  • Ammonia (high pH)
  • Algal toxins
  • Stress: temperature, pH, other wastewater constituents
wsp and wastewater reuse
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
Back to Big Picture
  • Complicated science ≠ Complicated solutions
  • Some treatment is better than no treatment
  • Current design approaches work
    • Attention to hydraulics!
    • Sludge management!