Composts

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Composts

• What is compost and why use it?
• What organisms are involved in the composting
  process?
• What chemical changes occur during composting?
• What are the optimal conditions for composting
• Temperature
• Moisture
• Oxygen
• Does composting kill harmful pathogens (plant and
  human), nematodes and weed seeds?
• Safety regulations
• Compost production systems
• Small scale
• Commercial

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What is compost why use it?
Composting is the decomposition of plant remains
and other once-living materials to make an
earthy, dark, crumbly substance that is excellent
for adding to houseplants or enriching garden
soil.

• compost improves soil structure, texture,
  aeration - increases the soil's water-holding
  capacity.
• Compost loosens clay soils and helps sandy soils
  retain water.
• improves soil fertility and stimulates healthy
  root development
• Organic matter provides food for microorganisms -
  nitrogen, potassium, and phosphorus mineralized

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The Science of Composting

• Composting is the natural process in which living
  organisms decompose organic matter into inorganic
  matter in the soil.
• The organisms feed on the organic material and
  through respiration generate the energy that they
  use for movement, growth, reproduction or stored
  energy.
• The organism excrete inorganic material that
  enriches the soil.
• When the organisms die, their bodies add to the
  organic matter in the compost pile.

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Fresh Organic Materials
Oxygen

Microbes, Moisture, and Time
Compost
Energy
Carbon Dioxide


Slide credit Tom Richard, Penn State University
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Organisms use carbon as a source of energy and
nitrogen to grow and reproduce.

• Too little N
• there will be few microorganisms, and
  decomposition will be slow.
• Too much N
• some will turn to ammonia that will volatilize,
  creating an odor.

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Experimental test - effect of CN ratio on
nitrogen retention in compost

Initial CN ratio Final nitrogen Nitrogen conservation

1 20 1.44 61.2
2 20.5 1.04 51.9
3 22 1.63 85.2
4 30 1.21 99.5
5 35 1.32 99.9
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Factors affecting the compost process
CN ratio
Size and texture
Aeration
NB. Moisture level also critical
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Moisture level is also critical

• Optimum moisture content 40-60
• Feels moist to touch, but when squeezed only
  produces few drops

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Ideal conditions for composting
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The Science of Composting

• Composting goes through three distinct phases
  that can be characterized by temperatures.
• Mesophilic Phase (moderate temperature)
• Thermophilc Phase (high temerpature)
• Mesophilic Phase (moderate temperature again)

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The Science of Composting

• Mesophilic Phase 1 (10-40 0 C)
• Lasts only a few days
• Explosive growth of bacteria and fungi
• Rapid breakdown of soluble sugar and starches
• Thermophilic Phase (gt40 0 C)
• Can last from several days to several months
  depending on size of system
• Mixed population of heat loving organisms
• High heat helps breakdown of proteins, fats,
  tough plant material like cellulose
• High temperature (gt55 0C) kill weeds and pathogen
  harmful to humans
• Higher temperature (gt600C) kill organism needed
  for decomposition
• Mesophilic Phase 2 (10-40 0 C) Curing Phase
• Can last several months
• Bacteria, fungi, actinomycetes( mix between
  bacteria and fungus, give earthy smell)
  predominate. Invertebrates active.
• Supply of organic material has decreased.
  Remaining organic material is slowly broken down.
  
• Additional chemical reactions take place to make
  remaining organic material more stable

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The Science of CompostingChemistry

• Important factors in compost chemistry
• Carbon-Nitrogen Mix (C/N Ratio)
• Carbon provides energy source and building
  material for 50 of composting organisms cells
• Nitrogen important in formation of proteins,
  nucleic acids, amino acids, enzymes etc. for
  organisms
• 301 Carbon to Nitrogen optimum mix (decreases in
  curing phase)
• Brown and woody? carbon
• Green and moist? nitrogen

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The Science of CompostingChemistry

• Important factors in compost chemistry
• Oxygen
• Needed to oxidize carbon for energy
• Without oxygen will produce rotten egg smell
• pH Level
• Acids form as organisms digest organic material
  and lowers pH
• Lower pH encourages fungi and the break down of
  tough matter
• If pH too low (lt4.5) limits microorganisms
  activity

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Changes in Ammonium-N distillation method fresh
sample
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Changes in Carbon to Nitrogen Ratio
Dan Sullivan and Linda Brewer
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Changes in cation exchange capacity(ash-free pH
7)
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Temperature
Fatty acids
NH3 emitted
pH
days
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Compost chemistry - pH
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The Science of CompostingPhysics

• Important factors for compost physics
• Temperature
• 3 Phases
• Want to maintain temperature between 55-600C
• Temperature impacted
• Heat generated by organism
• Heat lost to environment through conduction,
  convection and radiation ? shape and size of pile
• Moisture content (specific heat and heat capacity
  of water)

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The Science of CompostingPhysics

• Important factors for compost physics
• Particle size
• Microorganism activity occurs on surface of
  organic material
• The more surface area for organisms to attack,
  the quicker the decomposition ? want smaller
  particles
• Flip-side The smaller the particles, the more
  dense and compact the material resulting in poor
  oxygen circulation

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The main players

1. Bacteriamajor decomposers, breakdown simpler
   forms of organic material
2. Actinomycetesdegrade complex organics such as
   cellulose, lignin, chitin, and proteins earthy
   smell, long spider webs filaments
3. FungiBreak down tough debris, too dry, too
   acidic or too low in nitrogen for bacteria to eat

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What do microbes in compost do?

• Consume organic matter to grow
• Stabilize organic matter
• Aerobic oxidation produces CO2
• Anaerobic produces reduced compounds organic
  acids, alcohols
• Mineralize nutrients
• Organic to inorganic forms (protein to NH4)
• Transform nutrients
• Nitrification pH and temperature sensitive
• NOTE invertebrates not important in high
  temperature composting, only in cold

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Compost Quality

• Compost Maturity and Nitrogen Release
  Characteristics in Central Coast Vegetable
  Production
• July 2002
• CA Integrated Waste Management Board
• Marc Buchanan, PhD

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Compost Maturity
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Compost Maturity
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Compost Quality Measures
CN below 25
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COMPOST QUALITY INDEX for Commercial
Products Based on 13 monthly samples for green
waste, 11 for blend, and 1 poultry manure compost.
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Inorganic N release Spring and summer 2000
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Growing Issue

• How effective is composting at killing pathogens?
• Weeds, plant disease organisms
• Human pathogens!!!!

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U.S.A. Composting Regulations

• Biosolids, Class A compost (U.S. EPA 40 CFR Part
  503)
• Time-temperature relationship (PFRP)
• Static aerated pile, 3 days gt 55 C
• Turned windrow, 15 days gt 55 C, turned at least
  5 times
• Vector Attraction Reduction
• 14 days, 40 C minimum, 45 C average temperature
• Pathogen testing criteria
• Fecal Coliforms lt 1000 MPN/g TS
• or Salmonella lt 3 MPN/4g TS
• USDA National Organic Program 205.203 (c)
• Time temperature 55 C 70 C (CFR Part 503)
• Turned windrow 15 days with at least 5 turns
• In-vessel or static aerated system 55 C 70 C
  for 3 days
• CN ratio 251 401 (NRCS code 317 composting
  facility)

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• Why turn windrows at least 5 times in 15 days?
• Prevent regrowth of Salmonella
• Non-uniform heating
• Turn cooler material into insulated center

gt 55 C
Done properly it works, but can less intensive
regimes work too?
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NOSB Compost Task Force

• Composting regulations too prescriptive
• Manage compost to reach 55 C for 3 days
• Vermicompost
• Aerobicity maintained by adding thin layers every
  1-3 days
• 70-90 moisture
• 12 months for outdoor windrows, 4 months for
  wedge systems or indoor containers, 2 months for
  vertical flow reactors
• Processed manure
• Heat to 65 C for 1 hour
• Dry to lt 12 moisture
• Negative for Salmonella and fecal coliforms

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Animal pathogen destruction

• Meet current time-temperature standards
• Will not eliminate all weed seeds or all plant
  pathogens
• Attain sanitation target for particular end-use,
  quality assurance testing
• Use technology that is financially attainable
• Composting process
• Contain and treat leachate
• Exclude vectors
• Avoid pathogen regrowth conditions
• Avoid recontamination of product

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Compost production systems

• Small scale

Compost piles need to be at least one cubic to
hold the heat from decomposition
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Passive composting
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Commercial composting

• Large scale
• Passive aeration with turning or actively aerated
  systems

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Feedstock conditioning - grinding
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Moisture management - most important factor to
stabilize biological and chemical properties
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Processing turned windrows
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Compost blankets to moderate moisture
www.vanierselcompost.com/. ../productie.htm
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Composting - windrow
Turning helps aeration and to move material from
edge into hot center region
CO2
Hot
O2
Cool
Graphic credit Tom Richard, Penn State
University
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Composting Static forced air
CO2

• Air forces heat outwards
• Some systems can switch direction to keep base
  core at high enough temperature
• Also helps control odor

Hot
O2
Cool
Graphic credit Tom Richard, Penn State
University
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Processing - forced aeration
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Hot ammonia kills!!!

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Contain, treat leachate
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Compost blankets beware moving from fresh to
curing
www.vanierselcompost.com/. ../productie.htm
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Cure compost with 40-50 moisture to promote
competitive microorganisms and avoid salmonella
regrowth
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CASFS Farm compost piles 2008