Lesson 5: Waste Processing and Separation

Goals:

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

• 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)
• Curbside (most successful)
• approximately 3500 operations nation wide
• 40% mandatory
• Drop-off centers - ‘igloos’
• Cans, glass, plastics, newsprint
• Low participations
• Non-recyclables often discarded to avoid diposal costs
• Buy back centers (bottle bills, ADF)
• 90% of containers recycled in bottle bill states
• 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)

Compacting

• Density increases as a result of:
• crushing
• deforming
• relocating individual items

Size reduction

• Reduce size, blend constituents, more uniform for processing, compaction more efficient
• Chippers used to process wood, brush, trees - selection based on max diameter of material to be processed
• Hammermills used to process logs, brush, stumps, plastic, tires, glass, C&D materials, asphalt, shingles
• vertical grinders (tub grinder)- fed vertically which can result in material fly away and safety problems

Tub Grinders

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

Horizontal Grinder

• Pulping
• Roll Crushing
• Granulating

Material Separation

• Binary - two output streams
• Polynary - more than two output streams

• Picking (Hand Sorting)
• Screens
• 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
• Opening size based on desired separation
• Removes under/over sized material, light/heavy components
• Trommel
• Cascading
• Cataracting

Rotary Trommel Screens

• Reciprocating and disc screens (rotating discs move solid waste across a screen)
• horizontal shaking screen (cleaner feeds)

Air classfication (Float/Sink separator)

Major MSW unit process (2nd to magnetic)

current of air used to effect material separation based on density, viscous drag.

Separates less dense, mostly organic materials from more dense, mostly inorganic fraction.

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