1. PROCESSING & RECOVERY

2. Second fundamental function of solid waste management.
Improves the efficiency of solid waste disposal and prepares solid waste for subsequent recovery of materials and energy.
Some material in solid waste can be recovered and recycled for manufacture of the same or new products.

3. RECYCLING
The recovery of solid waste components for possible use as raw materials.
Industries used recycled materials in manufacture as processing of raw materials is more economical than processing recycled materials
Support from the government and enforcing laws for wastes to be recycled
Future for recycling is bright

4. PROCESSING FOR RECOVERY OF MATERIALS FOR RECYCLING
To segregate solid waste components may be done at point of generation or at a central processing facility.
On site processing needs the cooperation of the waste producer.
Different containers for different wastes: paper, cans, bottles.
At central processing facility, segregation into components using screening, air classifying and magnetic separations.
Size reduction using shredders (hammer mill, flail mill and shear shredder), glass crusher and wood grinders.
Magnetic separation involved the use of electromagnet to separate the ferrous materials from the rest of the solid

5. Hammer mill
Mechanical impacts device in which the raw solid waste material is hit with force sufficient to crush or tear individual pieces of waste.
Size reduction between 25mm to 50mm.
A typical hammer mill is a 150 hp unit capable of processing about 12 tons of solid waste per hour.
Disadvantage – high cost and maintenance, noisy and cause dust generation

7. Screening Is a unit operation of separating feed into
Oversized and undersized products
Separation into light combustibles and heavy non-combustibleties
Recovery of paper, plastics and other light materials from glass and metals
Separation of glass grit, sand from combustibles materials
Separation of rocks and other oversized debris from soil excavated at construction site
Removal of oversized materials from combustion ash
Oversized products are those that do not pass the opening of the screen
Undersized products are those that do pass the opening at the screen
Screen can be classified as primary, secondary or tertiary screens depending on where in the flow sheet the unit is located
The screen with the largest size opening is called the primary screen.

8. Trommels or rotary screens
Is a primary screen
Placed ahead of all separations unit in a separation facility
Can be equipped with metal blades, use as bag breakers
Separate materials into several size fractions
Materials to be separated are introduced at front end of the inclined rotating trommel
Small particles will fall through the holes in the screen while oversized material will pass through the screen

10. An operating trommel processing mix waste

11. Vibrating screens Disc screens
Used to remove undersized materials from commingled waste
Process demolition and construction waste
Vibrate from side to side, vertically or lengthwise
To separate MSW are inclined and vertical motion
Vertical motion allows the materials to be separated to contact the screen at different locations each time
Disc screens
Consist of parallel set of horizontal shaft. The undersized material fall between the spaces of in the discs and oversized materials will ride over the top of the discs
Different sized materials can be separated using the same screen by adjusting the spacing between the rotating discs.
Advantages – self cleaning and adjustability with the respect to the spacing between the discs on the driving shaft

12. Density separation (air classification)
To separate light materials such as paper and plastics from heavier materials such as ferrous metal, based on the weight of materials in the air stream
If materials introduced in the air stream moving with sufficient velocity, the light material will be carried away with the air while the heavier material will fall in the countercurrent direction
Magnetic separation
Recover ferrous material from commingled and shredded waste
Ferrous material are recovered either after shredding and before air classification or after shredding and air classification

13. Densification (compaction)
Unit operation that increases the density of waste materials so that they can be stored and transported more efficiently – reduce handling and shipping cost
Several technologies are available – baling, cubing and pelleting
Bales are typically 1.5m3 in size weigh roughly 1 ton
Solid waste can be compacted under high pressures (700 kPa or 100 psi) in either vertical or horizontal process
Volume reduction may be expressed in terms of compaction ratio or in percent
An understanding of the relationship between percent volume reduction and compaction ration is important

14. % volume reduction = initial volume – final volume x 100 initial volume Compaction ratio = initial volume final volume

15. MRFS (MATERIAL RECOVERY FACILITIES)
To separate out commingled MSW.
Commingled MSW enters the MRF at the tipping point.
Then, accumulated wastes push into hoppers or loaded onto conveyor belts using front end loaders.
Conveyors carry the waste to the next stage which is the sorting system.
Manual sorting platform or a multi staged waste processing system designed to automatically remove different recyclables.
Shredders and pulverizers may be used prior to separation to sort material by size.
The extraction products sent through densifier, can flatteners and baling systems before stockpiling.

16. Layout and design should consider:
Waste deliveries
Material delivery rates
Loading rates including storage for peak times
Material flow and handling patterns
Performance criteria for equipment selection
Equipment
Environmental controls
Aesthetics
Issues for MRFs
Siting – remote locations as much buffer as possible
Environmental issues – traffic, noise, dust, odour, vector control, airborne, litter, aesthetics problems
Public health and safety – general public and employees
Economics – sensitive to market prices

17. COMBUSTION
Reduction in the volume (85 – 95% reduction) and weight of wastes that required disposal
Recovery of energy in the form of heat
Major concerns – air pollution and siting
Air pollution is controlled including furans, dioxins, NOx, SO2 and particulates
Clean gases are discharged to the stack
Ash and unburned material are quenched (cool with water)
The water and residue must be properly disposed of.

18. Types of combustors Issues Mass fired.
Use unseparated, commingled MSW. The energy content is extremely variable
RDF (Refuse Derived Fuel) fired.
Produced from the organic fraction and can be made with consistency to meet energy, moisture, ash content specifications
Forms include: shredded, fluff, pellets or cubes.
Air emissions are cleaner because metals and plastics not burned
Issues
Siting – remote location with plenty of buffer zone
Air emission – important consideration in the decision between mass fired and RDF systems
Disposal of residue, bottom ash, fly ash, scrubber product.
Typically disposed in landfill
Liquid emissions – sources: ash removal, wet scrubbers, washings and housekeeping, cooling tower
Economics