Lecture XVIII

Physics 367

Recycling and Reuse



The amount of waste material thrown away in the US is staggering:

2 kg/person/d
0.5 Mte/d

The is about the same volume as 500 houses -- and it must be added to landfills each day!

Gross residential and commercial discards by weight
and total gross waste 1960-1990 (megatonnes)

Material

1960

1965

1970

1975

1980

1985

1990

Paper, paperboard

27.2

34.5

40.2

39.1

49.7

55.9

65.3

Ferrous metals

9.0

9.2

11.5

11.2

10.5

9.9

10.5

Aluminum

0.4

0.5

0.7

1.0

1.6

2.1

2.3

Other metals

0.2

0.5

0.6

0.8

1.0

0.9

1.0

Glass

6.1

7.9

11.5

12.3

13.6

12.0

11.4

Plastics

0.4

1.3

2.8

4.1

7.1

10.5

13.1

Yard waste

18.2

19.6

21.1

22.9

25.0

27.3

28.7

Other waste

18.5

20.5

22.4

25.1

27.4

28.3

31.0

Total

80.0

94.0

110.8

116.5

135.9

146.9

163.3

The message: reduce, reuse, recycle before disposal.

Reduction: Packaging constitutes 30% of the waste stream in developed countries. Most paper products, other than newspapers, end up in landfills as original packaging! Industry does NOT pay the costs of disposal.

Should industry pay the cost of disposal? In Germany they do! This has had the following effect:

Reuse: what does this mean? Examples?

Recycling: is the breaking down of material into its components so that it can be reused as raw material again. Examples:

Why recycle?

Consider aluminum. At one time it was a compound (bauxite) in the ground. It had to be

dug up
transported to a smelter
refined
sent to a mill
formed into sheets
sent to a manufacturer.

If aluminum is recycled it has to be

collected
transported to a foundry
melted
sent to a mill
formed into sheets
sent to a manufacturer

So is this worth it? Is it easier to collect or dig up?

Most of our bauxite comes from Jamaica, Canada, and Australia.
In bauxite, the aluminum is about 20% (Al2O3).
Thus each tonne of aluminum produces 4 tonnes of waste.
Refinement of aluminum uses quite a bit of electricity.

The cost of refining aluminum is about 300 MJ/kg while the cost from scrap is about 7 MJ/kg. In addition, there are transportation savings, as well as disposal savings.

Facet of Production Energy Used (MJ/kg finished aluminum)
Ore Extraction (mine, dry, ship)  
   Caribbean bauxite

6
   South American bauxite

9
   Average

7
Production of alumina from ore  
   Caribbean bauxite

42-57

   South American bauxite

40-56

   Average

49
Production of aluminum from alumina  
   Electrode       Prebaked

208-272

                       Soderberg

246-277

   Cost of fluorine compounds and calcining

4-10

   Average

258
Overall energy cost from ore

314

Overall energy cost from scrap  
   Pure

6

   30-40% contaminated

25

Why not just get the cans out of landfills?

The least expensive way is to separate at the point of use ... this means you. About 60% of the aluminum cans in the U.S. (600 kilotonnes) are recycled each year.

Steel is another good example:

Energy Costs in making steel (MJ/kg)

 

Ore

Scrap
Coke (0.4 kg)

11.5

  
Coal (0.02 kg)

0.7

  
Electricity (46 kWh)

5.6

  
Fuel Oil (4 litre)

2.5

  
Tar, pitch (0.3 litre)

0.2

  
Natural gas (0.13 m3)

5.0

  
Coke gas (0.16 m3)

3.0

  
     
Total from Ore

28.5

  
Total from Scrap  

1.26

It is interesting to note that you get about 1 cent per pound of steel and about 25 cents per pound of aluminum ... Wxhy is that?

What about glass?

It takes almost as much energy to melt glass as to melt the silicon-dioxide/soda ash mixture at 1400 °C. Thus recycling is not so cost effective ... but it has other advantages ... . and it is not as good as reuse.

Paper

About half of the weight and volume in landfills is from paper. Recycling paper allows this volume to be used more effectively ... and saves some trees. Each tonne of newsprint saves 2.3 m3 of landfill space. It is interesting to note that in the US there were 9 paper mills that used recycled paper in 1989, there were 26 in 1996 ... also the value of newsprint went from $100per ton to $10per ton ... as recycling was expanded. Moreover some states have now put a tax on NON-recycled newsprint!

Plastic

Plastics are characterized as:
  • PET - polyethylene terphalate - #1 plastic (soda bottles)
  • HDPE - high-density polyethylene - #2 plastic (milk bottles)
  • PVC - polyvinyl chloride - #3 plastic (water bottles)
  • LDPE - low-density polyethylene - #4 plastic (plastic bags)

Only #1 and #2 plastic are recycled. It costs about $1500per ton to collect and process plastic worth $100per ton. Some of the reasons include the large labor costs to handle the plastic and that the various plastics are incompatible i.e., PVC burns where PET melts. The actual recycling of plastic in 1992 was 2.9%.

So should we use paper bags or plastic bags when we shop?

Paper
  • degrades quickly
  • pollutes more on being made
  • takes about 20-30 times the electricity.
Plastic
  • easy and cheaper to produce
  • will not degrade

Curbside recycling has picked up recently. Now 5000 communities serving 85 million people recycle.

This helps the landfill problem -- landfills close because of inadequate pollution control or because they are full (a city of 500,000 generates about 78,000 m3 of glass waste volume each year). In 1979 there were 20,000 landfills in the US; in 1991 there were 5,800. As a result disposal costs have risen by factors of 2-5!

Do landfills degrade what is in them? the answer is not so clear ... see Energy.

The bottom line (in the Northeast US) is that

burning trash costs about $65-110 per tonne
landfills cost $40-140 per tonne
recycling costs $20-30 per tonne

Reusable bottles can also make a difference. The energy cost associated with a throwaway container is 6-9 times the energy of the beverage! The dollar costs associated with the container are 50% of the cost of the beverage. And we make an incredible number of containers:

  • 40 billion glass
  • 10 billion steel
  • 10 billion aluminum

The counterarguments are

  • inconvenience,
  • health,
  • job quality,
  • costs.

What do you think?