Approaches to Rational Microbial Risk Assessment of Treated Biosolids

Transcription

1 Engineering Conferences International ECI Digital Archives Wastewater and Biosolids Treatment and Reuse: Bridging Modeling and Experimental Studies Proceedings Spring Approaches to Rational Microbial Risk Assessment of Treated Biosolids Charles Haas Drexel University Follow this and additional works at: Part of the Environmental Engineering Commons Recommended Citation Charles Haas, "Approaches to Rational Microbial Risk Assessment of Treated Biosolids" in "Wastewater and Biosolids Treatment and Reuse: Bridging Modeling and Experimental Studies", Dr Domenico Santoro, Trojan Technologies and Western University Eds, ECI Symposium Series, (2014) This Conference Proceeding is brought to you for free and open access by the Proceedings at ECI Digital Archives It has been accepted for inclusion in Wastewater and Biosolids Treatment and Reuse: Bridging Modeling and Experimental Studies by an authorized administrator of ECI Digital Archives For more information, please contact

2 Approaches to Rational Microbial Risk Assessment of Treated Biosolids Charles N Haas LD Betz Professor of Environmental Engineering Drexel University Philadelphia, PA, USA 1 / 21

3 Outline Introduction Risks from Pathogens in Biosolids Routes Pathogens Current US Biosolids Regulatory Outline For Pathogens Risk Assessment Framework Exposure tools & gaps Air Groundwater Land/Food Chain Surface Water Dose-Response Gaps Simplified Risk Approach End Matter 2 / 21

4 Introduction Biosolids Definition: Biosolids are the nutrient-rich organic materials resulting from the treatment of sewage sludge (the name for the solid, semisolid or liquid untreated residue generated during the treatment of domestic sewage in a treatment facility) When treated and processed, sewage sludge becomes biosolids Source: USEPA 3 / 21

5 Introduction Route of Accumulation into Biosolids Pathogens in wastewater may be reduced in several ways 1 Inactivation during treatment 2 Physical removal into solids then separated If the pathogens then survive sludge treatment, they will remain in the biosolids for disposal 4 / 21

6 Risks from Pathogens in Biosolids Routes Physical Application Methods 5 / 21

7 Risks from Pathogens in Biosolids Routes Pathways source: Teng et althe Open Environmental Engineering Journal, / 21

8 Current US Biosolids Regulatory Outline For Pathogens Biosolids Classification Many other (non-pathogen requirements) must also be met Class B Biosolids Require waiting time between application and public access, restriction on types of agriculture, and buffer zones Requires a process for significant reduction of pathogens (PSRP) Class A Biosolids Can be applied to land without restriction requires a process for further reduction of pathogens (PFRP) 7 / 21

9 Current US Biosolids Regulatory Outline For Pathogens Synopsis of Requirements PSRP (B) PFRP (A) fecal coliforms < /gm < 1000/gm Salmonella 1 log reduction < 3/4gm enteric viruses 1 log reduction < 1/4gm viable helminths < 1/4gm Certain processes can be designated specifically as PSRP s or PFRP s if they can be shown to consistently meet these requirements Note that none of this is explicitly risk based 8 / 21

10 Risk Assessment Framework QMRA Process Source: US EPA 9 / 21

11 Risk Assessment Framework Unique Aspects of Microorganisms Adverse effects may result from single or short term exposure Low concentrations lead to stochastic variability (Poisson and extra-poisson) Therefore models must be capable of describing short term fluctuations in space and time Most environmental fate & transport models have at least time averaging Models of treatment processes have not been well developed to describe pathogen removal and its variability 10 / 21

12 Exposure tools & gaps Air Data Needs 1 Emission rates (size distributed) varying climate, weather, application methods Near site air dispersion models with short averaging times Air decay rates of microorganisms f (RH, insolation) 11 / 21

13 Exposure tools & gaps Groundwater Data Needs 2 Complexities of unsaturated flow transport Decay rates in saturated and unsaturated flow Filtration efficiencies, attachment, detachment Because microorganisms (or particle laden microorganisms) are low concentration, need stochastic models 12 / 21

14 Exposure tools & gaps Land/Food Chain Data Needs 3 Survival of pathogens on soil (surface) Effect of different application practices Soil-hand transferrence Eating (pica) 13 / 21

15 Exposure tools & gaps Land/Food Chain Data Needs 4 Decay in soil, migration into subsurface Incorporation of pathogens into edible plant tissue (Multiplication), survival and decay in plant tissue Impact of post- harvest handling (field to table) 14 / 21

16 Exposure tools & gaps Surface Water Data Needs 5 Runoff and subsurface flow Decay and filtration removal processes Treatment of water supply (possible route might be shallow wells) 15 / 21

17 Dose-Response Gaps Dose Response Data Gaps-1 We know that microbial dose response to bolus doses can be well described by: p = 1 exp ( kd) (exponential) or [ p = d(21/α 1) N 50 ] α (beta-poisson) But describing multiple/repeated exposures remains a challenge 16 / 21

18 Dose-Response Gaps Dose Response Data Gaps 2 Missing data for some key pathogens Helminths Inhalation exposure to most agents (bacteria, viral, protozoal) Dermal pathogens Sensitive and susceptible subpopulations impact on infectivity 17 / 21

19 Simplified Risk Approach Simplified Approach Steady state performance and transport Assume infectivity in air, water, dermal identical incorporation uncertainty & variability Calculations in a spreadsheet environment with visual basic macros 18 / 21

20 Simplified Risk Approach Simplified Approach Example Results Cumulative risk from single land application 19 / 21

21 End Matter Research Needs While we have the tools to do a rough screening level risk assessment, to do a more thorough job, there are many areas of research that need to be done (some not unique to biosolids): Dose-response data on pathogens of concern via routes of interest Integration of multiple doses and doses via multiple routes (PBDRMs) Process performance models for pathogen removal incorporating variability in an explicit fashion Need underlying basic data on process parameters impact on pathogens Environmental fate and transport models predicting short term variability in exposure 20 / 21

22 End Matter Acknowedgements Colleagues: Patrick Gurian, Mira Olson (Spreadsheet Biosolids) Longtime Collaborators: Chuck Gerba (University of Arizona) Joan Rose (Michigan State) 21 / 21