Lesson 10:Composting
Objective: To describe general
topics associated with the composting operations.
- Describe the most commonly used composting processes.
- Explain basic concepts associated with aerobic and anaerobic degradation.
- Explain the environmental factors affecting degradation processes.
- Explain the operational techniques used to control composting processes.
Assignments:
- Quiz for Composting Lesson
Review:
Introduction
Definition:
Biological decomposition of organic constituents of wastes under controlled
conditions (approximately 70% of MSW is decomposable).
General Information
- In 1995 - at least 15 MSW composting operation in US
- Ten others have closed
- Dade Co., FL (closed) processed 800 tons/day using windrows
- Baltimore, MD facility processes 700 tons/day using a tunnel digester
- Yard Waste composting is the largest use of the composting process
- In 1995 - over 3,300 yard waste composting operation in US
Classified based on O2 use
- Aerobic
- High temperature
- Absence of odors
- Rapid decomposition
- Anaerobic
- Low temperature
- Odorous intermediate products
- Slow decomposition
- Minimum attention required
Environmental conditions and microbial process
- Only degradable and non-hazardous materials
- Mixing or mechanical aeration required in aerobic operations
- Temp - rises to >60° C
- If too high, >65° C destroys organisms
- Must be >50° C to destroy pathogens
- 50-60° C ideal
- Controlled through mixing and aeration
- Nutrients - often Nitrogen is limiting
- Moisture Content
- A moisture content of 50 to 70% is ideal
- Too low inhibits
- Too high - anaerobic condtions develop
- Particle size >1”
- Small to increase surface area
- Large to avoid anaerobic conditions
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Shreding Equiptment for Pre-Processing Compost Materials
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Composting Techniques
- Windrows
- 2-6 months for decomposition
- Triangular piles; 7’ high and 14-16’ wide
- Aeration
- Turning by front end loader
- Specific turning equipment
| Compost
Windrows Turned Using a Scarab |
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- Aerated Static Pile
- 6-12 weeks for decomposition
- Mechanically aerated piles
- Diffuser underneath pile, air
either blown or sucked through pile
- 10-12’ high
| Aerated
Static Pile |
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- In-Vessel
- <1 week composting time
- Plug flow
- MSW placed in a chamber or vessel
- Mixing mechanism
- Aeration
- Sequenced reactions (aerobic/anaerobic)
- Controlled moisture content
- Proprietary processes - expensive
Pre- and Post-Processing
- Pre-processing
- Size reduction, screening, magnetic separation
- Post-processing
- Screening to ensure degradation
- Curing to allow for continued microbial action at a slower rate
Page last updated March 23, 2017
by Dr. McCreanor
