1. 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

2. 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

3. 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.

4. + + + Fresh Organic Materials Oxygen Compost Energy Carbon Dioxide
Microbes,
Moisture,
and Time
Compost
Energy
Carbon
Dioxide + +
Slide credit: Tom Richard, Penn State University

5. 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.

6. Nitrogen conservation %
Experimental test - effect of C:N ratio on nitrogen retention in compost
Initial C:N 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

7. Factors affecting the compost process
C:N ratio
Size and texture
Aeration
NB. Moisture level also critical

8. Moisture level is also critical
Optimum moisture content 40-60%
Feels moist to touch, but when squeezed only produces few drops

9. Ideal conditions for composting

10. 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)

11. The Science of Composting
Mesophilic Phase 1 ( C)
Lasts only a few days
Explosive growth of bacteria and fungi
Rapid breakdown of soluble sugar and starches
Thermophilic Phase (>40 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 (>55 0C) kill weeds and pathogen harmful to humans
Higher temperature (>600C) kill organism needed for decomposition
Mesophilic Phase 2 ( 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

12. The Science of Composting: Chemistry
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
30:1 Carbon to Nitrogen optimum mix (decreases in curing phase)
Brown and woody carbon
Green and moist nitrogen

13. The Science of Composting: Chemistry
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 (<4.5) limits microorganisms’ activity

14. Changes in Ammonium-N distillation method; fresh sample

15. Changes in Carbon to Nitrogen Ratio
Dan Sullivan and Linda Brewer

16. Changes in cation exchange capacity (ash-free; pH 7)

17. Temperature
Fatty acids
NH3
emitted pH
days

18. Compost chemistry - pH

19. The Science of Composting: Physics
Important factors for compost physics:
Temperature
3 Phases
Want to maintain temperature between C
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)

20. The Science of Composting: Physics
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

21. The main players
Bacteria: major decomposers, breakdown simpler forms of organic material
Actinomycetes: degrade complex organics such as cellulose, lignin, chitin, and proteins – earthy” smell, long “spider webs” filaments
Fungi: Break down tough debris, too dry, too acidic or too low in nitrogen for bacteria to eat

22. 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

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

24. Compost Maturity

25. Compost Maturity

26. Compost Quality Measures
C:N below 25

27. COMPOST QUALITY INDEX for Commercial Products
Based on 13 monthly samples for green waste, 11 for blend, and 1 poultry manure compost.

29. Inorganic N release – Spring and summer 2000

32. Growing Issue How effective is composting at killing pathogens?
Weeds, plant disease organisms
Human pathogens!!!!

33. 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 > 55 C
Turned windrow, 15 days > 55 C, turned at least 5 times
Vector Attraction Reduction
14 days, 40 C minimum, 45 C average temperature
Pathogen testing criteria
Fecal Coliforms < 1000 MPN/g TS
or Salmonella < MPN/4g TS
USDA National Organic Program § (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
C:N ratio 25:1 – 40:1 (NRCS code 317 composting facility)

34. > 55 C Done properly it works, but can
Why turn windrows at least 5 times in 15 days?
Prevent regrowth of Salmonella
Non-uniform heating
Turn cooler material into insulated center
> 55 C
Done properly it works, but can
less intensive regimes work too?

35. 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 < 12% moisture
Negative for Salmonella and fecal coliforms

36. 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

37. Compost production systems
Small scale
Compost piles need to be at least one cubic to hold the heat from decomposition

38. Passive composting

39. Commercial composting
Large scale
Passive aeration with turning or actively aerated systems

40. Feedstock conditioning - grinding

41. Moisture management - most important factor to stabilize biological and chemical properties

42. Processing – turned windrows

43. Compost blankets to moderate moisture
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44. Composting - windrow CO2 Hot O2 Cool
Turning helps aeration and to move material from edge into hot center region
CO2
Hot O2
Cool
Graphic credit: Tom Richard, Penn State University

45. Composting – Static forced air
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

46. Processing - forced aeration

47. Hot ammonia kills!!!

48. Contain, treat leachate

49. Compost blankets – beware moving from fresh to curing
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50. Cure compost with 40-50% moisture
to promote competitive microorganisms and
avoid salmonella regrowth

51. CASFS Farm compost piles 2008