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, 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 nm No lipid membrane 0.5 – 1 μm “Respond” to environment 2 – 20 μm Thick shell μm Very 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 v s ~ 1 m/h (others are lower)  Design equation: Ayres et al. (1992)

Removal by Sedimentation Cryptosporidium and Giardia cysts  V s ~ 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 Nelson et al. (2004)

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

First-order inactivation rate constants in WSP sludge 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 O2O2 ROS O2O2 Indirect damage by endogenous sensitizers Indirect damage by exogenous sensitizers Based on work by Tom Curtis, Rob Davies-Colley

UVB UVA Visible Solar Spectrum

Pond water absorbs sunlight

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

Sunlight inactivation mechanisms in WSP Direct damage by UVB O2O2 ROS O2O2 Indirect damage by endogenous sensitizers Indirect damage by exogenous sensitizers

Sunlight Mechanisms MechanismVirusesBacteria Wave- lengths Water Quality Factors Direct UVBYes UVBClear water! Endogenous sensitizers NoYes UVB, 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 MechanismVirusesBacteria Proto- zoan cysts Helminth eggs Direct UVB Adenovirus, Poliovirus Crypto Endogenous sensitizers NA Campylobacter, Salmonella Exogenous sensitizers Ponds Norovirus, Poliovirus, Enterovirus Salmonella, Shigella, V. cholera, Campylobacter Crypto Remove by sedimentati on! 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 MechanismVirusesBacteria Proto- zoan cysts Helminth eggs Direct UVB Adenovirus, Poliovirus Crypto Endogenous sensitizers NA Campylobacter, Salmonella Exogenous sensitizers Ponds Norovirus, Poliovirus, Enterovirus Salmonella, Shigella, V. cholera, Campylobacter Crypto Remove by sedimentati on! 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!