The Science of Composting: Benefits, Process, and Conditions

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 + 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. Experimental test - effect of C:N ratio on nitrogen retention in compost

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 (10-40 0 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 (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

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 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)

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. 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 < 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 • C:N ratio 25:1 – 40:1 (NRCS code 317 composting facility)

34. 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 www.vanierselcompost.com/. ../productie.htm

44. 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

45. 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

46. Processing - forced aeration

47. Hot ammonia kills!!!

48. Contain, treat leachate

49. Compost blankets – beware moving from fresh to curing www.vanierselcompost.com/. ../productie.htm

50. Cure compost with 40-50% moisture to promote competitive microorganisms and avoid salmonella regrowth