Composting Practices and Pathogen Reduction

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Composting Practices and Pathogen Reduction

• Joan Jeffrey, Extension Veterinarian
• University of California
• School of Veterinary Medicine
• VMTRC---TULARE, CA

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Composting

• Heat generated by microbial activity
• Application of heat over time kills mesophilic
  bacteria and favors thermophilic bacterial
  population
• Bacteria in mature compost compete against and
  inhibit pathogen regrowth

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Composting methods

• Passive Aerated Static Piles or Windrows
• Stacked Pile
• Aerated Stacked Pile
• Windrow
• Enclosed System
• Containerized Systems (Aerated Static Piles in a
  box)

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Methods applicable to non-green waste

• Non-green waste food, dairy products,
  raw/cooked meat, dead animals (cows, poultry,
  fish)

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Methods applied to poultry carcasses

• Two stage bin composting
• Refers to 2 heating cycles
• Containerized system
• Reference FS 717 U. of Maryland

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Methods suitable for blood/feathers

• Windrow
• Most common method for green waste/manures
• gt3000 facilities in USA
• Rows 8 ft high x 12-16 feet wide
• Approved by EPA for pathogen destruction if
  windrows are turned 5x in 15 d and temperatures
  stay gt 131 F (55 C)
• Aerated Static Pile
• Piles 7 to 9 feet high connected to blowers
• Approved by EPA for pathogen destruction
• Requires 131 F (55 C) for 3 days

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Federal guidelines for pathogen destruction in
compost

• For windrows15 days, turned no less than 5
  times, temperature of 131 F (55 C)
• For aerated static piles3 days at temperature
  gt131 F (55 C)
• Governed by Code of Federal Regulations 40, CFR
  Part 503, 1993

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Killing of pathogens during composting

• Temperature (thermal kill)
• Ammonia (chemical kill)
• Microbial antagonism

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Rate of microbial decomposition

• A function of surface area
• i.e. whole carcasses would compost at a slower
  rate than tissues like blood or feathers

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Temperature-Time relationships for pathogen
reduction

• D-values time required for 1 log reduction in a
  pathogen at a given temperature
• Can compare hardiness of different organisms
• Used to establish pathogen elimination criteria

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Poultry pathogens addressed by specific studies

• Senne, D. A., et al. (1994) Highly Pathogenic
  Avian Influenza virus and EDS-76 Adenovirus
• Compost Bin method used with poultry carcasses
• Two-stage
• Turned after 10 days
• Average temperatures 57-58 C
• 1/20 tissues positive for adenovirus at d 10
• 0/20 tissues positive for virus at d 20

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Poultry pathogens addressed by specific studies

• Conner, D. E. et al. (1991)
• Fungi and coliform, aerobic, anaerobic,
  thermophilic and thermotolerant bacteria were
  represented
• S. enteritidis, S. typhimurium, S. seftenberg,
• L. monocytogenes, E. coli, P. multocida and
  Aspergillus fumigatus
• Used wheat straw, peanut hulls and other
  materials
• Pathogens placed into carcasses
• No bacteria after stage I of composting
• No fungal spores after stage II of composting

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Poultry pathogens addressed by specific studies

• Murphy, D. W. et al. (1990)
• Newcastle disease virus
• Infectious Bursal Disease virus
• Bin compost method for carcasses
• Two stage composting method

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Other pathogens addressed by specific studies

• M. tuberculosis (Morgan McDonald 69)
• Salmonella, Shigella, poliovirus, enterovirus,
  parasite cysts (Gaby 75)
• Coliforms, Salmonella, Ascaris ova (Hay 96)
• Salmonella, bacteriophage (Epstein 76 and
  others)

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Potential problems

• Recontamination by equipment, other vectors
• Regrowth
• Only possible for bacteriaa
• Studies cite salmonella and coliforms as most
  likely to regrow
• These organisms are used as indicators of
  pathogen elimination

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Use of indicator organisms to ensure pathogen
destruction

• Sampling for indicator organisms is conducted to
  validate composting processes (temperature/time)
  (USEPA 40)
• Temperatures are then verified for each compost
  pile or windrow
• Microbial sampling is generally not required for
  every batch assuming consistent feedstock and
  processing

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USEPA standards for Class A biosolids

• Fecal coliform level of lt 1000 MPN per gram of
  dry solids, OR
• Salmonella spp. level of lt 3 MPN per 4 gram of
  dry solids

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Conclusions

• Composting methods for pathogen destruction are
  well documented
• Monitoring of the composting process is a valid
  substitute for microbiologic testing

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Conclusions

• Studies addressing major poultry pathogens have
  been conducted
• Due to greater surface area, blood, feathers and
  processing waste should compost more rapidly and
  uniformly than carcasses