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. Top 10 Reasons to Compost
10.Be environmentally responsible.
9. Reduce need for chemical fertilizers, mulch.
8. Create a healthy landscape.
7. Improve the quality of your soil.
6. Reduce amount of yard waste going to landfill.
5. Protect the Chesapeake Bay and watershed.
4. Decrease water use in your landscape.
3. Protect privacy. Use shredded personal papers!
2. It's easy. Good exercise.
1. Free bin for Howard County residents!
#3 – some kids like to shred their homework – after they get it back from the teacher! Shred old credit card receipts.

4. 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.

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

6. 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.

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: 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

11. 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)

12. 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

13. 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

14. 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

15. Starting your Compost Pile
- Ideal size is 3 ft. x 3 ft. x 3 ft. (27 cubic ft.) Easier to turn, aerobic action
No larger than 5 x 5 x 5
Can become anaerobic
Here are more ideas for creating a workable bin in your yard. Cinder block works well – open side for easier turning. Wooden pallets make a great compost bin too – and allow for air circulation.

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

17. Passive composting

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

19. Vermicomposting
Vermicomposting is the process of using worms and micro-organisms to turn kitchen waste into a black, earthy-smelling, nutrient-rich humus.
The worms used in vermicomposting are called redworms (Eisenia foetida), also know as red wigglers, manure worms, red hybrid or tiger worms.

20. Feedstock conditioning - grinding

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

22. Processing – turned windrows

23. Compost blankets to moderate moisture
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24. 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

25. 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

26. Processing - forced aeration

27. Contain, treat leachate

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