Pathogens in WSP

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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….)

7. We already know a lot!

8. Main Removal Mechanisms • Sedimentation ( Sludge) • Helminth eggs • Protozoan cysts • Particle-associated bacteria and viruses • Sunlight-mediated inactivation • Viruses • Bacteria • Protozoan cysts

9. Removal by Sedimentation Helminth eggs • Ascaris eggs vs ~ 1 m/h (others are lower) • Design equation: Ayres et al. (1992)

10. 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)

11. Removal by Sedimentation • Viruses and Bacteria • Only if attached to particles • High concentrations in sludge

12. Sludge distribution in Xalostoc

13. 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)

14. Long vs stub baffles Shilton and Harrison (2003) “Guidelines for the hydraulic design of waste stabilization ponds”

15. Sludge Management • Pathogens are concentrated in the sludge! • Sludge accumulation can decrease treatment performance • Decreased HRT • Change hydraulics

16. Apparent inactivation of helminth eggs in sludge cores Nelson et al. (2004)

17. Inactivation of indicator organisms Sludge cores Batch test Nelson et al. (2004)

18. First-order inactivation rate constants in WSP sludge Nelson et al. (2004)

19. Implications • Survival times in sludge • Ascaris – years • Viruses – months to years • Bacteria – weeks to months • Sludge (most likely) requires treatment upon removal

20. 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

21. Solar Spectrum UVB 280-320 UVA 320-400 Visible 400-700

23. Pond water absorbs sunlight

24. Sunlight penetration in WSP 290 nm 550 nm Depth (cm)

25. ROS O2 Sunlight inactivation mechanisms in WSP Direct damage by UVB O2 ROS Indirect damage by endogenous sensitizers Indirect damage by exogenous sensitizers

26. Sunlight Mechanisms *MS2 not sensitive to high pH

27. 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)

28. 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)

29. 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

30. 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

31. 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

32. “Dark” inactivation mechanisms • Predation • Ammonia (high pH) • Algal toxins • Stress: temperature, pH, other wastewater constituents

33. 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

34. Back to Big Picture • Complicated science ≠ Complicated solutions • Some treatment is better than no treatment • Current design approaches work • Attention to hydraulics! • Sludge management!