Lesson 8: Waste Processing and Separation

Goals:

• Describe the most common waste processing techniques.
• Develop process flow charts for material separation.

Read:

• Text, Chapter 5 excluding the appendix (pp. 173-210)
• Text, Chapter 6 (pp. 224-275)
  • Carefully Review:
    • Materials Separation Systems (pp. 269- 272)
    • Pay particular attention to the figures (6-34, 6-35, and 6-36)

Assignments:

• Quiz for Waste Processing and Separation Lesson

• Processing is used to alter the physical characteristics of the waste stream or to remove particular components from the stream
• Landfill mining, a technique used to reclaim landfill air-space, uses separation processes to remove recyclable and decomposable components of the previously disposed waste.
• Processed materials may be used
  • Directly
  • As raw materials for remanufacturing or reprocessing
  • As a feed stock for compost productor other chemical or biological conversion
  • As a fuel source, refuse derived fuel (RDF)
  • For land reclamation (composted waste)

Separation at source (manual)

1. Curbside (most successful)
   1. @3500 opoerations nation wide
   2. 40% mandatory
2. Drop-off centers - ‘igloos’
   1. Cans, glass, plastics, newsprint
   2. Low participations
   3. Non-recyclables often discarded to avoid diposal costs
3. Buy back centers (bottle bills, ADF)
   1. 90% of containers recycled in bottle bill states
   2. Bottle bill effect on curbside?

Separation at a materials recovery facility (MRF)

Clean MRF - Processing of separated materials (baling, crushing, etc.)
Dirty MRF  - Separation of commingled MSW
    *Both improve the quality of the recovered material (cleaning, separation of glass/plastics, contam removal, densification)

Size reduction

• Review Text Chapter 5, Shredding (pp. 183-207); Granulating (pp. 210)
  • Reduce size, blend constituents - more uniform for processing
  • Chippers used to process wood, brush, trees - selection based on max diameter of material to be processed
  • Grinder and Hammermills used to process logs, brush, stumps, plastic, tires, glass, C&D materials, asphalt, shingles
  • Tub grinders - fed vertically which can result in material fly away and safety problems

Tub Grinders

VIDEO: Tub Grinder - Model 2009 - DuraTech

• Horizontal grinders - utilizes a fully contained grinding chamber fed horizontally via a conveyor belt which eliminates fly away and reduces safety concerns 

  Horizontal  Grinders

  VIDEO: Vermeer HG8000TX Horizontal Grinder

• Glass crushers
• Compaction
• Roll crushing - WATCH VIDEO

Size Separation

• Review Text, Chapter 6
  • Used to:
    • Remove fines from material prior to processing
    • Grade ground or crushed materials particulary concrete
    • Separate glass, Al cans, cardboard
    • Post-process compost to ensure complete degradation
  • Screening techniques used include- vibrating screen, rotary scree, disc screen
    • Opening size based on desired separation
    • Removes under/over sized material, light/heavy components

    • Rotary Trommel Screens
      VIDEO: Doppstadt 720 Trommel Screen

  • Air Classification
  • Major MSW unit process (2nd to magnetic) - current of air used to effect material separation based on density, viscous drag
  • Separation of light organics (combustable) fraction from heavy inorganics
  • Use declining due to lack of shredding
  • VIDEO: De-Stoner® Air Classifier / Density Separator for cleaning rocks from wood

Mechanical Separation Techniques for Specific Materials

Ferrous metal - magnetism (most successful and efficient unit process)

Glass - froth flotation, optical separation tried in ‘70s but not efficient

Non-ferrous metals - flotation, electromagnetic eddy current, electrostatic separation tried, concentration and efficiency low

Plastics - no mechanical separation device in US source separation or hand picking, proprietary means used in Europe

Video: Can Sorter and Eddy Current Can Separator