PRINCIPLES OF COMPOSTING

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PRINCIPLES OFCOMPOSTING
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Principles of Composting

• What Is Compost?
• The product resulting from the controlled
  biological decomposition of organic materials
• Sanitized through the generation of heat
• Stabilized to the point where it is beneficial to
  plant growth
• Provides humus, nutrients, and trace elements to
  soils

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Organic Materials

• Landfill wastes (food, wood, textiles, sludges,
  etc.)
• Agricultural wastes (plant or animal)
• Industrial manufacturing byproducts
• Yard trimmings
• In short, anything that can be biodegraded

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Unsuitable Materials

• Pet wastes
• Animal remains (meat, fish, bones, grease, whole
  eggs, dairy products)
• Invasive weeds and plants

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Why Compost?

• Agricultural wastes ? potential for nutrient
  pollution
• Compost benefits to soil 25 lbs N, 13 lbs P (as
  P2O5), and 7 lbs K (as K2O) per ton of compost
• Environmental sustainability

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Compost Benefits

• Physical Benefits
• Improved soil structure, reduced density,
  increased permeability (less erosion potential)
• Resists compaction, increased water holding
  capacity
• Chemical Benefits
• Modifies and stabilizes pH
• Increases cation exchange capacity (enables soils
  to retain nutrients longer, reduces nutrient
  leaching)
• Biological Benefits
• Provides soil biota healthier soils
• Suppresses plant diseases

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More Compost Benefits

• Binds heavy metals and other contaminants,
  reducing leachability and bioabsorption
• Degrades petroleum contaminants in soils
• Enhances wetlands restoration by simulating the
  characteristics of wetland soils
• Coarser composts used as mulch provide erosion
  control
• Can provide filtration and contaminant removal of
  stormwater pollutants

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The Composting Process

• Biological decomposition in aerobic environment
• Decomposition mineralization by microbes
• Bacteria, actinomycetes, fungi, protozoans,
  nematodes
• Food source Nitrogen (biodegradable organic
  matter)
• Energy source Carbon (bulking agent)

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The Composting Process

• Outputs
• Heat
• Water Vapor
• Carbon Dioxide
• Nutrients and minerals (compost)
• Process occurs naturally, but can be accelerated
  by controlling essential elements

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Composting Essential Elements

• Nutrients
• Carbon/Nitrogen (C/N) 201 to 351
• Carbon/Phosphorus (C/P) 1001 to 1501
• Moisture Content 50 to 60 (wet basis)
• Particle Size ¼ to ¾ optimum
• Porosity 35 to 50
• pH 6.5 to 8.0
• Oxygen concentration - gt5
• Temperature 130o F. to 150o F.
• Time one to four months

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Nutrient Balance in Composting

• C/N ratio target is 301
• gt 301 not enough food for microbial population
• lt 301 nitrogen lost as ammonia (odors)
• Sources of N P - Organic wastes, manures,
  sludges, etc.
• Sources of C wood wastes, woodchips, sawdust
• Example C/N Ratios
• Food waste 14 16 1
• Refuse/trash 34 80 1
• Sewage sludge 5 16 1
• Corrugated cardboard 563 1
• Telephone books 772 1
• Mixing components needed to optimize C/N ratio

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Moisture Content

• Source of nutrients for microbial protein
  synthesis and growth
• Optimum water content 50 to 60 (wet weight
  basis)
• lt 50 - composting slows due to microbial
  dessication
• gt60 - compaction, development of anaerobic
  conditions, putrefaction/fermentation (odors)
• Water may be needed during mixing, composting
• Yard wastes 40 to 60 gallons per cubic yard
• Typical moisture contents
• Food wastes 70
• Manures and sludges 72 - 84
• Sawdust 19 - 65
• Corrugated cardboard 8
• Newsprint 3 - 8

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Particle Size Distribution

• Critical for balancing
• Surface area for growth of microbes (biofilm)
• Adequate porosity for aeration (35 - 50)
• Larger particles (gt 1)
• Lower surface area to mass ratio
• Particle interior doesnt compost lack of
  oxygen
• Smaller particles (lt 1/8)
• Tend to pack and compact
• Inhibit air flow through pile
• Optimum size very material specific

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pH

• Optimum range 6.5 8.0
• Bacterial activity dominates
• Below pH 6.5
• Fungi dominate over bacteria
• Composting can be inhibited
• Avoid by keeping O2 gt 5
• Above pH 8.0
• Ammonia gas can be generated
• Microbial populations decline

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Porosity and Aeration

• Optimum porosity 35 - 50
• gt 50 - energy lost is greater than heat produced
  ?lower temperatures in compost pile
• lt 35 - anaerobic conditions (odors)
• Aeration controls temperatures, removes
  moisture and CO2 and provides oxygen
• Airflow needs directly proportional to biological
  activity
• O2 concentration lt 5 - anaerobic conditions

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Time and Temperature

• Temperature is key process control factor
  monitor closely
• Optimum temperatures 130o F. 150o F.
• Temperatures above 131o F. (55o C.) will kill
  pathogens, fecal coliform parasites
• Temperatures gt 131o F. for 15 days in windrows
• Optimum temps achieved by regulating airflow
  (turning) and/or pile size

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Windrow Composting

• Materials mixed and formed into windrows
• Windrows 7 8 wide, 5 6 tall, varying
  lengths
• Compost turned and mixed periodically
• Aeration by natural/passive air movement
• Composting time 3 6 months

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Windrow Composting, cont.

• Equipment Needed
• Grinder/Shredder
• Tractor/FEL
• Windrow Turner
• tractor-pulled
• self-propelled
• Screener
• One Acre Can Handle 4,000 - 7,000 CY Compost Mix