Transcript Document
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) Viruses: Hepatitis A, Rotavirus, Norovirus, Poliovirus Protozoa: Cryptosporidium, Giardia, Entamoeba Bacteria: Vibrio cholera, Salmonella, Shigella, Campylobacter Helminths: Ascaris, Taenia, Trichuris, Hymenolepis Pathogens in water (The bad guys) 20-100 nm No lipid membrane Viruses: Hepatitis A, Rotavirus, Norovirus, Poliovirus 2 – 20 μm Thick shell Protozoa: Cryptosporidium, Giardia, Entamoeba 0.5 – 1 μm “Respond” to environment Bacteria: Vibrio cholera, Salmonella, Shigella, Campylobacter 20 - 100 μm Very thick shell Helminths: Ascaris, Taenia, Trichuris, Hymenolepis 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 Design equation: 4.9 0.0085 R 100 1 0.41e (others are lower) 2 Ayres et al. (1992) Removal by Sedimentation Cryptosporidium and Giardia cysts Vs ~ 2.5 cm/h Particle association may be important Design equation (Robertson et al. 1999) (Grimason et al. 1993) Removal by Sedimentation Viruses and Bacteria Only if attached to particles High concentrations in sludge Sludge distribution in Xalostoc 12 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 1000 Mexicaltzingo Viable eggs/g TS Texcoco 100 Xalostoc Expon. (Xalostoc) Expon. (Texcoco) Expon. (Mexicaltzingo) 10 1 0 2 4 6 8 10 Estimated sludge age, yrs Nelson et al. (2004) 12 14 Inactivation of indicator organisms 1 Log removal Sludge cores Somatic coliphage F+ coliphage Fecal coliform Fecal enterococci 0 2 3 4 0 2 4 6 8 10 12 14 Estimated sludge age, yrs 0 Batch test Log removal 1 2 3 4 0 1 2 3 4 Time, months Nelson et al. (2004) 5 6 7 8 First-order inactivation rate constants in WSP sludge k, d-1 Organism Ascaris eggs Mexicaltzingo Texcoco Xalostoc Sludge cores 0.0009 0.0007 0.0010 Indicator organisms (Xalostoc) Somatic coliphage 0.0016 F+ coliphage 0.016 Fecal coliform 0.13 Fecal enterococci 0.26 Nelson et al. (2004) Batch test Dialysis chambers 0.0021 0.0074 0.037 0.16 0.20 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 O2 ROS ROS O2 Direct damage by UVB Indirect damage by endogenous sensitizers Indirect damage by exogenous sensitizers Based on work by Tom Curtis, Rob Davies-Colley Solar Spectrum UVB 280-320 UVA 320-400 Visible 400-700 1.8 Measured Irradiance (W/m 2) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 270 370 470 570 Wavelength (nm) 670 770 Pond water absorbs sunlight 1.8 1.0 0.8 1.4 1.2 0.6 1.0 0.8 0.4 0.6 0.4 0.2 0.2 0.0 270 370 470 570 Wavelength (nm) 670 0.0 770 Absorbance Measured Irradiance (W/m2) 1.6 Sunlight penetration in WSP 0 290 nm 550 nm Depth (cm) 2 4 6 Depth (cm) 8 10 0.0 0.2 0.4 0.6 0.8 1.0 Irradiance (W/m 2) 1.2 1.4 Sunlight inactivation mechanisms in WSP O2 ROS ROS O2 Direct damage by UVB Indirect damage by endogenous sensitizers Indirect damage by exogenous sensitizers Sunlight Mechanisms Water Quality Factors Viruses Bacteria Wavelengths Direct UVB Yes Yes UVB Clear water! Endogenous sensitizers No Yes UVB, UVA High DO 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* Mechanism Exogenous sensitizers *MS2 not sensitive to high pH Sunlight Mechanisms Mechanism Direct UVB Endogenous sensitizers Viruses Bacteria Adenovirus, Poliovirus Protozoan cysts Helminth eggs Crypto NA Campylobacter, Salmonella Norovirus, Poliovirus, Enterovirus Salmonella, Shigella, V. cholera, Campylobacter Remove by sedimentati on! Exogenous sensitizers Ponds Crypto 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 Direct UVB Endogenous sensitizers Exogenous sensitizers Ponds Viruses Bacteria Adenovirus, Poliovirus Protozoan cysts Crypto Remove by sedimentati on! Campylobacter, Salmonella NA Helminth eggs Need to fill these boxes! Norovirus, Poliovirus, Enterovirus Salmonella, Shigella, V. cholera, Campylobacter Crypto 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! 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 Laboratory Sunlight varies Can’t separate variables 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!