Impacts of Anaerobic Digestion and Solid Liquid Separation on Pathogen Destruction


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A study was conducted to evaluate the pathogen inactivation on 9 dairy facilities in Wisconsin with a combination of anaerobic digestion and solid/liquid separation technologies. Samples were collected every 2 weeks over the course of eight months to assess dairy pathogen inactivation in full-scale operational digesters and solid/liquid separators. Samples were then analyzed by qPCR for pathogens including protozoa, bacteria. bovine viruses, and indicators.

Preliminary results indicate full-scale anaerobic digesters reduce pathogen levels by 99% to 99.9%. And after digestion and separation of the digestate, the liquid fraction contains the majority of pathogens. Although the solids fraction contained fewer pathogens, the concentration could still be above the infectious dose, particularly for calves. Results have implications for a variety of digestate end uses including bedding and land spreading.

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Impacts of Anaerobic Digestion and Solid Liquid Separation on Pathogen Destruction

  1. 1. INACTIVATION OF DAIRY MANURE-BORNE PATHOGENSBYANAEROBIC DIGESTIONBecky Larson, Asli OzkaynakApril, 3, 2013Mark Borchardt, Susan Spencer, and Spencer BorchardtUSDA –Agricultural Research ServiceUSGS Wisconsin Water Science Center
  2. 2. Pathogens in Cattle ManureBacteria(e.g., Campylobacter, Salmonella, E. coli O157:H7)Viruses(e.g., adenovirus, enterovirus, rotavirus)Protozoa, (e.g., Cryptosporidium, Giardia,Eimeria)
  3. 3. Cryptosporidium parvum• Scours in calves• Responsible (with C. hominis) for largest waterbornedisease outbreak in US history• Severe diarrhea 21 days median duration• 7-22% of patients hospitalized• Deadly infection in AIDS patients andimmunocompromised• Infected children have reduced growth
  4. 4. Toxin producing E. coli• E. coli O157:H7• No disease in cattle• Severe diarrhea; 4% of cases developkidney failure• 73,000 cases, 60 deaths/year in US• Walkerton, Ontario outbreak
  5. 5. Salmonella enterica• In cattle, diarrhea, milk drop, abortion, rapid death incalves• In people, diarrhea, cramps, fever• Can move from the intestine to bloodstream, bone, andurinary tract• 1.4 million cases, 600 deaths/year in US• Growing antibiotic resistance• Drinking raw milk presents high risk of infection
  6. 6. Campylobacter jejuni and C. coli• Most common cause of bacterial gastrointestinal illness inthe US• Debatable among veterinarians whether a cattle pathogen• Severe diarrhea, potential complications withliver, heart, other organs• Causes Guillain-Barré syndrome, acute paralysis
  7. 7. Other zoonotic pathogens in cattle manure- Infrequent human health effectsMicrosporidia Leptospira speciesBrucella species Listeria monocytogenesBacillus anthracis Mycobacterium bovisClostridium perfringens Apthovirus (foot andmouth disease)Coxiella burnetiSourcesDungan, RS. 2010. J. Anim. Sci. 88:3693-3706Atwill, ER. Et al. 2012 . NRCS Technical Note No. 9
  8. 8. Pathogens in manure from a single farm byyear and seasonAutumn, 2007Autumn, 2008Spring, 2009
  9. 9. Pathogens in manure from a single farm byyear and seasonAutumn, 2009Spring, 2010Autumn, 2010Spring, 2011
  10. 10. Anaerobic Digesters …• Produce methane for generating electricity and heat• And…• Might, as an added side-benefit, inactivate/destroypathogens in manure that can potentially pose a risk tothe health of humans and livestockOperational principle of sanitation since Louis Pasteur•Reducing the number of pathogens reduces the level of exposure whichreduces the risk of infection•Principle works at small scale (hand sanitizers) to large scale wastewaterand drinking water treatment plants
  11. 11. Current Knowledge• Mesophilic anaerobic digestion can reduce by 99% to99.9% the levels of several microbes: E. coli, fecalcoliform bacteria, fecal streptococci, Listeriamonocytogenes, Salmonella senttenberg.• Thermophilic anaerobic digestion is more effective thanmesophillic digestion in removing pathogens• Pathogen removal depends on temperature, pH, andretention period
  12. 12. Key Knowledge Gaps• Pathogen inactivation in full-scale operational digesters.• Pathogen-specific inactivation rates for the complete arrayof pathogens potentially present in dairy manure.• Operational parameters of full-scale digesters mostimportant for pathogen removal• Pathogen levels in final solids component used for cowbedding
  13. 13. Study Objectives• Measure pathogen inactivation by farm-scale anaerobicdigestion of dairy manure• Evaluate several factors for their effect on pathogeninactivation (pathogen type, farm, time of year)• Determine proportion of surviving pathogens in digestateliquid and solid fractions after separation• Determine effect of bedding recovery units (no digestion)on fractionation of pathogens into liquids and solids
  14. 14. Study Overview• Nine farms sampled for ~ 10months• Sample between manureprocessing components• Measure nutrients, solids, andpathogens• 2 digester types (all mesophilic)• Plug Flow (5)• Completely Mixed (2)• 4 separator types• Screw press (6)• Centrifuge (1)• BRU (2)Filtrate(Liquid)ScrewPressFiber(Solid)Plug FlowDigesterFiltrate(Liquid)RotatingDrumFiber(Solid)ScrewPressFiltrate(Liquid)ScrewPressFiber(Solid)CompletelyMixedDigester
  15. 15. Anaerobic Digester – CompletelyMixed and Plug Flow
  16. 16. Separator - Screw Press
  17. 17. Separator - CentrifugeCentrifuge - Dane County Digester; Clear Horizons
  18. 18. Separator - Bedding Recovery Unit
  19. 19. Pathogens and Indicators AnalyzedProtozoa Bovine VirusesCryptosporidium parvum Rotavirus groups A and CGiardia lamblia EnterovirusAdenovirusPolyomavirusBacteria Bovine viral diarrhea virus types 1 and 2Enterohemorrhagic E. coli CoronavirusCampylobacter jejuniSalmonella enterica IndicatorsClostridium perfringens Bovine bacteroidesMycobacterium avium paratuberculosis Bacteroides-like M3Bacteroides-like M2
  20. 20. Pathogens Detected during StudyProtozoa Bovine VirusesCryptosporidium parvum Rotavirus group AGiardia lamblia Rotavirus group CEnterovirusAdenovirusPolyomavirusBovine viral diarrhea virus type 1Bacteria Bovine viral diarrhea virus type 2Enterohemorrhagic E. coli CoronavirusCampylobacter jejuniSalmonella enterica IndicatorsClostridium perfringens Bovine bacteroidesMycobacterium avium paratuberculosis Bacteroides-like M3Bacteroides-like M2
  21. 21. Logarithm (Log) Removal• The logarithm of the pathogen concentration in the manureminus the logarithm of the pathogen concentration in thedigestate• 1 log removal = 90% reduction• 2 log removal = 99% reduction• 3 log removal = 99.9% reduction, etc.For plug flow digesters the digestate concentration used inthe log removal calculation was offset by two samplingperiods from the manure concentration to account forretention time of approximately 21 days.
  22. 22. Digester Removal by Pathogen Type
  23. 23. Digester Removal of Bacteroides by Farm
  24. 24. 11010010001000010000010000001000000010000000MeanPathogenConcentration(gc/gm) Bovine BacteroidesFarm #1Farm #3Farm #4Farm #5Farm #6Farm #7Farm #8
  25. 25. Digester Removal of Polyomavirus by Farm
  26. 26. 110100100010000100000100000010000000100000001E+09MeanPathogenConcentration(gc/gm) Bovine PolyomavirusFarm #1Farm #3Farm #4Farm #5Farm #6Farm #7Farm #8
  27. 27. Digester Removal of Bacteroides over TimeLogRemoval
  28. 28. Digester Removal of Coronavirus over TimeLogRemoval
  29. 29. Digester Reduction in Percentage Detections1 3 4 5 6 7 8
  30. 30. Digester Reduction in Percentage Detections
  31. 31. Liquid/Solid FractionationBovine Bacteroides020406080100120Farm1 Farm3 Farm4 Farm5 Farm6 Farm7 Farm8LiquidSolidPercent
  32. 32. Liquid/Solid FractionationBovine PolyomavirusPercent020406080100120Farm1 Farm3 Farm4 Farm5 Farm6 Farm7 Farm8LiquidSolid
  33. 33. 11010010001000010000010000001000000010000000ManureSeparated LiquidSeparated Solid 1Separated Solid 2MeanPathogenconcentration(gc/gm) Separated Bedding: Bovine BacteroidesFarm #2Farm #9
  34. 34. 110100100010000100000100000010000000ManureSeparated LiquidSeparated Solid 1Separated Solid 2MeanPathogenconcentration(gc/gm)Separated Bedding: Bovine PolyomavirusFarm #2Farm #9
  35. 35. Study Limitations• Sampling frequency was not based on digester retentiontime therefore the manure and digestate samples are nottruly coupled, particularly for the plug-flow digesters.• Measured inactivation of pathogen/indicator genomes;this is not a measure of infectivity or viability.• Pathogen concentrations in many samples were near theassay limit of detection, which reduces accuracy of the logremoval estimate
  36. 36. Preliminary Conclusions• Full-scale anaerobic digesters reduced pathogen levels by 90%to 99.9%• Removal efficiency varied by pathogen type, farm, and time• After digestion and separation of the digestate, the liquidfraction contained the majority of pathogens.• Separation of undigested manure by bedding recovery unitsresulted in the liquid fraction containing the majority ofpathogens.• Although the solids fraction contained fewer pathogens, theconcentration could still be above the infectiousdose, particularly for calves• Heating/drying the solids should result in complete pathogeninactivation but this was not always the case (process control?)
  37. 37. Does Anaerobic Digested Manure haveReduced Health Risks?Findings and perspectives to keep in mind…• Pathogen types and concentrations in manure(i.e., the herd) are highly variable over time• Pathogen inactivation by anaerobic digestionis highly variable• Because pathogen concentrations in manurecan be very high, a 99% reduction (i.e., 2-logremoval) does not mean pathogen levelsbecome low• 99% of the pathogens in the digestate afterseparation partition into the liquid fraction• Digesters are designed to producemethane, not inactivate pathogens.
  38. 38. Current Work: Manure Irrigation