Source separation of plastic wastes yields and qualities from a pilot study in Norway

Waste Management & Research (1983) 1, 249-254

SOURCE SEPARATION OF PLASTIC WASTES YIELDS AND QUALITIES FROM A PILOT STUDY IN NORWAY Sigrun Bekkevold* (Received 11 July 1983) Source separation experiments in some selected commercial and industrial establishments showed that the individual establishment participating in the sortering, had a yearly generation of polyethylene (PEL) foil waste of 0 .4-2 .8 t, corresponding to 7-168 kg/employee each year . There were no problems of separating PEL foil from other waste components . Difficulties consisted in removing attached contaminants (labels and tape) and there was a general positive attitude by employees concerning participation in a permanent source separation process and even in improving the sorting procedure . The regenerated plastics showed satisfactory properties for applications in refuse sack production, but the degree of contamination of the input material was generally higher than acceptable for an extrusion process . Extensive plastic recycling based on source separation of consumer waste would require mechanical wet refining/sorting before regeneration to prevent frequent clogging of extruder filters . However, refining might be omitted for wastes from a few careful selected establishments . Based on the present price situation for PEL, mechanical baling of plastic wastes before transportation is necessary . Key Words-Source separation, plastic waste, plastic recovery, Norway .

1 . Introduction Owing to a considerable increase in the use of plastic packagings, causing high amounts of plastic wastes to be disposed of, a considerable interest in recycling of these materials has appeared . The objectives are both to minimize environmental problems and to save resources . The Norwegian Ministry of Environment therefore initiated a project at The Foundation of Scientific and Industrial Research at the Norwegian Institute of Technology (SINTEF) to carry out some practical source separation experiments based on plastic packaging wastes in trade and industry . Private households were not included because of inhomogenity of the household waste . Plastic waste from trade and industry are more homogeneous and also cleaner, consisting mostly of transportation packagings . The experiments were carried out in Trondheim in 1982 followed by test runs of the sorted plastics in a regeneration plant for plastic wastes . The reason for the plastic recycling was to replace virgin plastic materials with recycled plastic waste . The experiments were reported in a SINTEF-report (Bekkevold 1983) and are summarized below .

2 . Types and amounts of recycleable plastic wastes in Norway Polyethylene-low density (PEL) is the most common polymer used as plastic packaging

*A/S Miljeplan, N-1300 Sandvika, Norway .

0734-242X/83/030249 + 06 $03 .00/0

© 1983 ISWA



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S. Bekkevold

TABLE 1 Consumption and waste generation of PEL foil (1000 t/year) Waste Plastics

Consumption Household Trade/indusry

PEL foil Shopping bags Shrink foil Sacks/bags Other packaging

44

Total

15

22

37

7 1

1 9

7

12

8 10 8 11

and thus contributes to the largest portion in consumer plastic wastes . Polyethylene is mainly used as foil, i .e . shopping bags, shrink foil, refuse sacks, etc . The plastic wastes will also contain certain amounts of polyvinyl chloride (PVC) foil and crates or containers of polyethylene-high density (PEH) in addition to bottles, cups and cans of either PVC, PEH, PEL or polystyrene (PS) . Regarding recycling, PEL foil is currently of most interest in Norway and other European countries . Table 1 gives an estimate of the amounts of PEL foil in consumer waste and the total consumption of PEL foil in Norway . These values are based on statistics and previous research . (Bekkevold 1976 ; Hämäläinen 1981 ; Lukkedal 1979; Nunn & StremErichsen 1976) . In addition waste is generated in the form of used agricultural foil and leftover foil from building activities . 3. Source separation experiments 3 .1 . General problems Source separation of plastic wastes implies separate storage of plastics from other types of waste at the sources before collection and transportation to a recycling plant . A plastic recycling plant contains agglomorators, extruders and granulators . The main problem is to get a sufficiently clean and homogeneous plastic material, and this depends on the quality of the source separation, i .e . removing impurities like PVC foil and labels, tape, etc . attached to the foil . In some cases it may be difficult to distinguish PEL from PVC foil . Contamination of the plastic fraction by PVC results in a low quality product . Private households throw away considerable amounts of PEL foil as shopping bags, which is the most interesting plastic component for recycling . However, investigations at SINTEF, including analysis of household waste by manual sorting, showed that more than 80% of these bags were used as refuse wrappings and were thus unavailable for recycling in a source separation system . 3 .2 . Selected establishments Ten establishments were selected as test plastic waste sorters . The selection was based on interviews of more than 120 establishments in Trondheim and Kristiansand . Table 2 gives an outline of the selected establishments . 3 .3 . Equipment/procedure The equipment used for storage of sorted plastic wastes was 1 .2 m 3 palleted containers .



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251

TABLE 2 Description of selected establishments in terms of branches, no . of employees and duration of sorting No. of employees time/part time)

Duration of sortings (weeks)

2 3 4

Retail trade Supermarket A Supermarket B Building materials Carpets

1/6 25/15 16/8 6/1

9 4 2 4

5 6 7 8

Wholesale Grocery A Grocery B Grocery C Fruits and vegetables

50/6 25 80/10 30/2

4 4 4 7,5

300 60

8 4

Establishment no . 1

9 10

Branches

Industry Brewery Feed producer

(full

The total height of the containers was 1 .3 m . Sorted plastic waste was collected every week by replacing full containers with empty ones . Some of the establishments were equipped with baling compactors, normally used for compacting waste paper . In the plastic sorting period these were used for baling of sorted plastics . The Paper Recycling Central in Trondheim handled the physical collection and transportation . Pallet wrappings are normally shrink foil, but also stretch film may be used for this purpose . Shrink foil is always made of PEL while either PEL or PVC can be the basis for stretch film . To ensure collection of only PEL plastics the establishments were asked to exclude all stretch film from the sortings and also, when possible, to remove labels . 3 .4 . Analysis of collected plastics wastes

The collected waste was weighted and the quality analysed with regard to contaminants . The results from the analysis are given in Tables 3 and 4 . Analysis of the plastics was done by sorting and registration of undesirable components like stretch films and individual non-plastic components (paper, metals etc .) . Limitations of the experiments, regarding both duration and number of participating establishments, produce constraints on the drawing of conclusions . However, the results give some indications on both yields and qualities which showed considerable variation . More than 50% of the establishments generating stretch film waste, did keep this away from the collection as requested . Generally the content of non-PEL components in the collected plastics was low, but removal of labels, tape, etc . was in most cases not perfect . Having completed the experiments the establishments were interviewed about their attitude towards a prospective regular sorting . With one exception, they were all positive and it was a predominant opinion that a better sorting, with respect to removal of impurities, is possible . The importance of information and motivation was strongly emphasized .



25 2

S . Bekkevold

Amounts

TABLE 3 collected plastics during the experiment period and calculated yearly plastic waste generation

of

Establishment no .

Collected plastics (kg)

Average yearly amounts (kg)

Spec . generation (kg/employee and year)

1

108 26 42 79 126 142 217 322 307 134

624 388 1092 1027 1638 1846 2821 2230 1995 1742

168 lI 55 158 32 74 33 72 7 29

2 3 4 5 6 7 8 9 10

TABLE 4 Results from the analysis of collected waste plastics (weight %) Establishment/ sample no . 1 2 3 4 5 6 7 8 9

10

PEL fraction

Stretch film

Others

98 .0 100 95 .5 99 .7 100 96 .5 92 .5

0 0 3 0 0 3 .5 7 .5

2 .0* 0 1 .5t 0 .3$ 0 0 0

100

0

0

100

0

0

Not sorted

*Paper, metal wire and strings . t Mainly paper . :Mainly metal wire . H = high and L = low degree of labels, tape, etc. attached to the plastics ; to the plastics .

N =

Comments on PEL fraction Dirty H Clean L Dirty H Clean H Clean L Clean L-H Clean L Dirty H Clean N Very dirty N

no labels, tape, etc. attached

4. Regeneration The sorted and compacted PEL fractions were sent to a regeneration plant for quality assessment and regeneration . The regeneration process consists of agglomoration, extrusion and granulation . The extruder was equipped with a 60 mesh filter for detaining possible impurities . Based on visual evaluation the plastics from establishment nos 3 and 10 were excluded from further processing due to high degree of contamination . Also no . 6 was excluded, because of high similarity with no . 5 . Attached contaminants were totally removed from sample no . 7 and partly removed from no . 4. Samples 1 and 2 were combined . The other samples were processed without any further refining .



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253

Filter shifts

Sample no .

7

I 10

9 1 20

I 5 30

2

81

40

50

4

I 60

-

Time (min) Fig . 1 . Extrusion process .

A total of 650 kg was regenerated of which 150-200 kg was processed in a way that made identification of the different samples possible . During extrusion the filter was changed automatically when the pressure exceeded a certain value due to clogging by contaminants . The frequence of filter shifts and the melting index of the extruded plastics were recorded as quality indicators of the plastics . Figure 1 illustrates the extrusion procedure, i .e . duration of extrusion for the individual samples and the time of filter shifts . During extrusion of the remaining 450-500 kg plastic waste, a total number of 14 filter shifts were recorded, i .e . an average of 35 kg/filter shift. Assuming that the extruder was run with a capacity of 250 kg/h, the filter was changed on the average every 8-9 min . Although some of the samples were only transparent shrink foil, the extrusion process always resulted in granules of a grey colour . This is mainly due to dust content . Table 5 shows the results from the melting index analysis . All the samples had a melting index within the interval which is normal for foils made of virgin PEL (0 .3-0 .5) . TABLE 5 Melting index of the plastic samples (190 °C/2 .16 kp)

Sample no . Melting index (g/10 min) 1+2 4 5 7 8 9

0 .49 0 .41 0 .35 0 .38 0 .39 0 .26

The main conclusions from the regeneration experiments were : • The quality of the regenerated plastics was satisfactory for production of thick foil, i .e . refuse sacks . • With the exception of sample nos 7 and 9 from wholesale grocery C and a brewery, (respectively), regeneration of the plastic wastes showed an unacceptable high filter shift frequence . This causes reduced capacity of the plant and thus lower revenues .



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• Extensive plastic recycling based on source separation will probably require mechanical wet refining and/or sorting before regeneration to prevent frequent clogging of extruder filters . However, careful selection of establishments may make refining unnecessary but will reduce the volume of the recycled plastic . 5 . Economy The economy of sorting, collection and storage of plastic wastes was investigated . Sorting and collection without mechanical compaction is not economical, even when savings in present waste handling costs are taken into account . Because of the extremely low density of plastic foils mechanical compactors must be used before storage . This is due to the considerable increase of transportation efficiency leading to reduced collection costs per tonnes of waste . A multi chamber baler is applicable for this purpose as this can be used for other waste components such as paper thus causing savings in the total waste handling costs in establishments with large waste generation . Owing to lack of balance between production and demand for PEL plastics in Europe the market situation is not very favourable regarding prices for regenerated plastics . References Bekkevold, S . (1983), Source separation of plastics from trade and industry, SINTEF report no . STF21 A83035, Trondheim . Nunn, D . & Strom-Erichsen, A . (1976), Mass flow analysis of plastic wastes . Energy aspects and recycling, CMI report 75093, Bergen . Hämäläinen (1981), Statistical review of the packaging industries in Scandinavia 1975-1979, European Packaging Statistics Group . Helsinki . Lukkedal, B . (1979), Plastic wastes in Norway-amounts and utilization possibilities, SINTEF report STF21 F79077, Trondheim .