COMPOSTING

 

www.geocities.com/shalasya/composting.html

San4:Solid Waste Disposal                                    Shalasai Huangprasert

I.   Definition

  1. Biological decomposition of organic constituents of wastes under controlled conditions
  2. 70% of MSW is decomposable . How about the composition of BKK solid wastes?

II.   General Information

  1. In 1995 - at least 15 MSW composting operation in US
    1. Ten others have closed
    2. Dade Co., FL (closed) processed 800 tons/day using windrows
    3. Baltimore, MD facility processes 700 tons/day using a tunnel digester
  2. Yard Waste composting is the largest use of the composting process
    1. In 1995 - over 3,300 yard waste composting operation in US
  3. In Thailand, Organic Composting had been campaigning for Sustainble Agriculture, and H.M. New Theory of Agriculture.
  4. Various kinds of liquid org fertilizers as Bio-augmentator,Bio-seeds, Bio-accererators and E.M. were introduced.

III.   Classification based on O2 use

  1. Aerobic
    1. High temperature
    2. Absence of odors
    3. Rapid decomposition
  2. Anaerobic
    1. Low temperature
    2. Odorous intermediate products
    3. Slow decomposition
    4. Minimum attention required

IV.   Environmental conditions- microbial process

  1. Non-hazardous material
  2. Aerobic - mixing or mechanical aeration required
  3. Temp - rises to >60° C
    1. If too high, >65° C destroys organisms
    2. Must be >50° C to destroy pathogens
    3. 50-60° C ideal
    4. Controlled through mixing and aeration
  4. Nutrients - often Nitrogen is limiting
    1. 50-70% moisture content ideal
    2. Too low inhibits
    3. Too high - anaerobic condtions develop
  5. Particle size >1”
    1. Small to increase surface area
    2. Large to avoid anaerobic conditions

V.   Technology

  1. Windrows
    1. Triangular piles; 7’ high and 14-16’ wide
    2. Aeration
      1. Turning by front end loader

Compost turned with a front
end loader

Compost windrow. Note:
processing equipment in background

      1. Specific turning equipment

Compost Windrows Turned Using
a Scarab

    1. 2-6 months for decomposition
  1. Aerated Static Pile

Aerated Static Pile

    1. Mechanically aerated piles
      1. Diffuser underneath pile, air either blown or sucked through pile
    2. 10-12’ high
    3. 6-12 weeks for decomposition
  1. In-Vessel - (plug flow)
    1. MSW placed in a chamber or vessel
      1. Mixing
      2. Aeration
      3. Controlled moisture content
    2. Proprietary processes - expensive
    3. <1 week composting time


VI.   Pre and Post Processing

  1. Pre
    1. Size reduction, screening, magnetic separation
  2. Post
    1. Screening
    2. Curing continued microbial action at a slower rate

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