recycling of plastics_a materials balance optimisation model.pdf

8/18/2019 Recycling of Plastics_A Materials Balance Optimisation Model.pdf

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Recycling of Plastics A Materials Balance

Optimisation M ode l

P. F O L K E R T S T A R R E V E L D * a nd E K K O C . V A N I E R L A N D * *

Bd t3 Consultants, Researcher, Rot ter dam ; Wageningen Agr icul tura l University,

Environmental Economist , Department o f General Economics, P.O. Box 8130,

6700 E W Wageningen, the Netherland s

Abstract At present the volume of solid waste produced in mode rn consumer societies is

increasing, requiring policy measures to reduce the volume of waste to be dumped or

incinerated. In th is article a materials balance optimisation model fo r the recycling of plastics

is developed to analyse the impact o f policy measures that stimulate recycling. The study

presents the structure of the optimisation model and it gives the results of a charge imposed

on the dum ping and incineration o f plastics. The calculations sho w that considerable effort

should be made to reach the recycling targets for plastic that have been set by the public

authorities for the year 2000.

Key words

Recycling, plastics, waste management, environmental econom ics, optimisation,

materials balance.

I n t r o d u c t i o n

T h e i n c r e a s i n g v o l u m e o f s o l i d w a s t e p r o d u c e d i n m o d e r n c o n s u m e r s o c i e t y

r e q u i r e s p o l i c y m e a s u r e s t h a t r e d u c e t h e q u a n t i ti e s o f w a s t e t o b e d u m p e d o r

i n c i n e ra t e d . T h e o p t i m a l m e t h o d o f tr e a t in g p l a s ti c w a s t e c a n b e c a l c u l a te d

b y m e a n s o f a n o p t i m i s a t i o n m o d e l g i v e n v a r i o u s c o n s tr a i n ts . S u c h a m o d e l

m a k e s i t p o s s i b l e t o e s t a b l is h t h e i m p a c t o f v a r io u s e n v i r o n m e n t a l p o l i c y

i n s t rum en t s on t he r a t e o f r ecyc l i ng o f p l a s t ic p rod uc t s and p l a s t i c m a t e r i a l s .

L a r g e q u a n ti t ie s o f p l a st i c w a s t e s a r e p r o d u c e d a n n ua l ly . D e s p i t e c o n -

s i de rab l e e f fo r t s to i m p l em en t m o re r ecyc l ing , the t o t a l quan ti t ie s o f was t e

a re s t i l l g rowi ng . P rope r was t e t r ea t m en t f ac i l i t i e s a r e no t gene ra l l y ava i l ab l e

t o t r ea t th i s was t e a nd l a rge quan t i t ie s o f was t e a r e d um pe d o r i nc i ne ra t ed .

Th e i nc i ne r a t i on o f p l a s t ic s l eads t o cons i de r ab l e em i s s i ons o f d iox i n wh i ch

a r e d e t r im e n t a l t o h u m a n h e a l t h e v e n i n t h e s m a l le s t q u a nt it ie s . A b o u t 1 o f

t h e t o ta l v o l u m e o f w a s t e p r o d u c e d i n t h e N e t h e r l a n d s c o n s is t s o f p l as ti c s

and t he u se o f p la s t ic s i s i nc reas i ng annua l l y , m a i n l y bec ause t he l i gh t we i gh t

and du rab i l i t y o f p l a s ti c s l end i t a di s t inc t ad van t a ge ov e r som e o t he r

m a t e r i a l s .

P u b l i c a u t h o r i t i e s i n t h e E u r o p e a n C o m m u n i t y h a v e t r i e d t o s t i m u l a t e

was t e p rev en t i o n and r ecyc l i ng , bu t w i t h l it tl e succes s. 1 In t he Ne t he r l ands ,

a n e f f o r t is b e i n g m a d e t o r e c y c l e a b o u t 4 2 o f p l as t ic s b y t h e y e a r 2 0 0 0

( M i n i st r y o f P h y s ic a l P l a n ni n g, H o u s i n g a n d E n v i r o n m e n t , 1 9 8 9 ). A t p r e s e n t ,

on l y abo u t 10 i s ac t ua l l y be i ng r ecyc l ed . In abso l u t e quan ti t ie s , the am ou n t

Environmental and Resource Economics 4:251--264, 1994.

© 1994 Kl uw er Ac ad em ic Publishers. Printed in the Netherlands.


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2 5 2

P F o l k e r t S t a r r e v e ld a n d E k k o C V a n [ e r l a n d

o f r e c y c l e d p la s ti c s i n t h e y e a r 2 0 0 0 h a s t o b e 5 t im e s a s h i g h a s a t p r e s e n t .

F i g u r e 1 g iv e s a n e s t i m a t e o f q u a n t it i es o f p la s ti c w a s t e i n t h e N e t h e r l a n d s

f o r 1 9 8 6 , 1 9 9 4 a n d 2 0 0 0 .

u a n t i t i e s o f p l a s t i c w a s t e

in t h e e t h e r l a n d s

1 0

8 5 0 . 0 0 0 6

to

2 6

9 0 6 8

9 5 0 . 0 0 0

t o R

1 9 8 6 1 9 9 4 2 0 0 0

Y e a r

[ ]

Dum ping inc inerat ion ~ Recycl ing [~ W aste prevent ion

Fig. 1. Quan tities of plastic waste in the Netherlands 19 86 (dum ping, recycling and waste

prevention) and targets for 1994 and 2 000.

A l s o , th e p o l i c y ta r g e ts a r e i n d i c a te d . D a t a f o r T h e N e t h e r l a n d s h a s b e e n

u s e d a s a c a se s t u d y f o r t h e e m p i r i c a l v a l i d a t i o n o f t h e o p t i m i s a t io n m o d e l .

I n th i s a r ti c le t h e s t r u c t u r e o f t h e m a t e r ia l s b a l a n c e o p t i m i s a t i o n m o d e l

a n d t h e m o d e l r e s u lt s a r e d i s c u ss e d .

1 T h e A i m o f t h e O p t i m i s a ti o n M o d e l

D e s p i t e m a n y o p t i o n s f o r t h e u s e o f p l a st ic w a s t e m a t e r i a l, t h e r e - u s e a n d

r e c y c l in g o f p l a st ic s is l im i t e d to a b o u t 1 0 o f t h e a n n u a l v o l u m e o f w a s t e .

I n c o m p a r i s o n t o o t h e r m a t e r i a l s l i k e p a p e r a n d g l a s s , t h i s p e r c e n t a g e i s v e r y

l ow . If th e c o n d i t io n s n o w p r e v e n t i n g t h e m o r e f r e q u e n t r e c y cl in g a n d r e - u s e

o f p la s ti c s w e r e m o d i f i e d , b e t t e r r e s u l ts c o u l d b e a c h i e v e d . T h e l i m i t e d s iz e

o f t h e m a r k e t f o r r e c y c l e d p l a s ti c a n d t h e l o w p r o f i t a b i l it y o f p l a st ic r e c y c l i n g

a r e t h e m a i n , o b s t r u c t i n g c o n d i t i o n s . I f p u b l i c a u t h o r i t i e s a r e t o r e a c h t h e


3/14

R e c y c l i n g o f P la st ic s 2 5 3

sp ec i f i ed p o l i cy t a rg e t s , t h en th e se b a r r i e r s sh o u ld b e r em o v ed in c lo se co -

o p e ra t io n wi th p l a s t i c p ro d u ce r s an d co n su m er s . Pu b l i c au th o r i t i e s h av e a

n u m b er o f p o l i cy in s t ru m en t s av a i lab le , su ch a s ch a rg es an d su b s id ie s o r

d i r ec t r eg u la t io n s fo r d ep o s i t sy s t em s (Bau m o l an d Oa te s , 1 9 8 7 ) . Th e ch o ice

o f p o l i cy in s t ru m en t s i s m a in ly d e te rm in ed b y th e e f f ec t iv en ess an d e f f i c ien cy

o f th e in s t ru m en t s . To se l ec t t h e o p t im a l p o l i cy in s t ru m en t s , a m a te r ia l s

b a l a n c e o p t i m i s a ti o n m o d e l m a y b e h e l pf u l. T h e m o d e l i s d e s ig n e d i n s u c h a

way th a t we can sh o w th e im p ac t o f a f u e l t ax an d an in c r ease in was te

d u m p in g t a r i f f s o n th e r a t e o f r ecy c l in g an d was te d u m p in g . Recy c l in g o f

was te s i s n o t o n ly b en e f i c i a l i n r ed u c in g th e v o lu m e o f was te , b u t i t m ay

a l so c o n t r i b u t e t o e n e r g y c o n s e r v a t i o n a n d t h e r e d u c t i o n o f C O 2 e m i s s io n s

( O k k e n

e t a l .

(eds) , 1989) .

H erea f t e r , w e d i scu ss th e m a in s t r u c tu r e o f t h e m o d e l an d th e t ech n ica l

p o ss ib i l i t i e s f o r r ecy c l in g p la s t i c s . We a l so an a ly se wh ich eco n o m ic f ac to r s

p lay a r o l e in th e d ec i s io n -m ak in g p ro cess o n th e r e -u se an d r ecy c l in g o f

plast ics.

2 Techn ical Asp ects

In g en e ra l, t h e fo l lo win g p o ss ib i l it i e s f o r t h e r ed u c t io n o f th e v o lu m e o f w as te

p las t ics a re d is t ingu ished : :

w a s t e p r e v e n t i o n . W a s t e p r e v e n t i o n c a n b e e f f e c t e d b o t h o n t h e p r o d u c -

t io n a n d t h e c o n s u m p t i o n s i d e o f th e e c o n o m y . T h e p l as ti cs i n d u s tr y

co u ld ex p lo r e p ro cesse s th a t r ed u ce th e was t in g o f p l a s t i c s in th e p ro d u c -

t i o n p r o c e s s . C o n s u m e r s c o u l d r e d u c e t h e q u a n t i t y o f p l a s t i c w a s t e b y

u s in g wrap p in g m a te r i a l s an d b ag s th a t c an b e u sed sev e ra l t im es , i n s t ead

o f t h r o w - a w a y p a c k i n g m a t e r i a l s )

p r o d u c t r e c y c l i n g . P r o d u c t r e c y c l i n g m a k e s i t p o s s i b l e t o u s e t h e s a m e

p ro d u c t sev e ra l t im es . Th e ad v an tag es o f p ro d u c t r ecy c l in g can b e

r ea l i sed in th e co n se rv a t io n o f en e rg y an d m a te r i a l s i n p ack ag in g an d

d i s t r ib u t io n in d u s t r i e s , f o r ex am p le , wh e re b o t t l e s an d c r a t e s a r e r e -u sed .

m a t e r i a l r e c y c l i n g . Mate r i a l r ecy c l in g o f p l a s t i c s h a s two ap p l i ca t io n s : t h e

m a te r i a l m ay r ep lace s im i l a r m a te r i a l s o r i t m ay b e u sed to r ep lace o th e r

m a te r i a ls , l i k e p ap e r o r a lu m in iu m . A d i sad v an tag e o f m a te r i a l r ecy c l in g

i s th a t i t i s o f t en im p o ss ib l e to u se th e m a te r i a l f o r t h e o r ig in a l p u rp o se .

P l a s t i c s b e c o m e p o l l u t e d w h e n t h r o w n a w a y w i t h o t h e r w a s t e m a t e r i a l .

A l so th e q u a l i ty o f r ecy c le d p la s t ic i s m u ch lo w er th an th a t o f v i rg in

m a te r i a l . I n s t ead o f a f u l l r ecy c l in g p ro cess , a seq u en ce o f d eg rad a t io n o f

m a te r i a l q u a l i ty is tak in g p lace . Wa s te g en e ra t ed f ro m h igh q u a l i ty p la s t ic

i s u l t im a te ly t r an s fo rm ed in to lo w q u a l i ty (m a te r i a l r ep lac in g ) ap p l i ca -

t io n s . 4 Th e s t ag es o f d eg rad a t io n can b e sh o w n b y m ean s o f a so - ca l l ed

cascad e d iag ram (F ig . 2) . Th e r a t e o f d eg rad a t io n can b e r ed u ce d b y th e

av o id an ce o f p o l lu t io n , an d th e m ix in g o f d i f f e r en t p l a s ti c s , im p lem en t in g


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2 5 4

P Folkert Starreveld and Ek ko C Van lerland

Q u a l i t y -

r e q u i r e m e n t s

o f t h e u s e r s

, , V i r g i n - m a t e r i a l

r e q u i r e d

e g r a n u l a t e m a d e o f

w a s t e o ~ h i g h e r o r

e q u a l i z e d

a p p l i c a t i o n s

i o l

R a t e o f p o l l u t i o n

o f t h e

m a t e r i a l

Fig. 2. An exam ple of a cascade diagram for three stages according to V NC I, 1989).

w e l l - d e s i g n e d s y s t e m s o f se p a r a t e g a r b a g e c o l l e c t io n . A n o t h e r w a y to

a c h i e v e h i g h q u a l i t y r e c y c l e d m a t e r i a l s i s t h e s e p a r a t i o n o f m i x e d q u a n -

t it ie s o f p l a st ic s f r o m o t h e r h o u s e h o l d w a s te . H o w e v e r , t h e c o s ts o f t h e s e

t e c h n i q u e s a r e v e r y h ig h a n d f u ll y a u t o m a t i c s e p a r a t io n s e e m s t o b e

i m p o s s i b l e a t p r e s e n t .

T h e r m a l c o n v e r s i o n h y d r o l y s i s , p y r o l y s is , g a s if ic a ti o n ). A p a r t f r o m t h e

a b o v e m e n t i o n e d t e c h n i q u e s , m e t h o d s a r e a v a il a bl e t o d e c o m p o s e p l a st ic s

b y m e a n s o f t h e r m a l c o n v e r s i o n te c h n i q u e s . T h i s is s o m e t i m e s c a l l e d

t e r t i a r y r ec y c l in g . T h e a d v a n t a g e o f th e s e s y s te m s i s t h a t t h e y c a n b e u s e d

f o r q u a n t i t ie s o f m i x e d p l a s ti cs , t o s o m e e x t e n t. T h e r e m a i n i n g f r a c t i o n s

c a n b e u s e d t o f a b r i c a t e n e w p l as ti cs , s

3 . E c o n o m i c A s p e c t s

A n i m p o r t a n t p r e - r e q u i s i t e f o r r e c y c l in g is e c o n o m i c fe a si b il it y . T h e r e c y c l -

i n g i n d u s t r y s h o u l d h a v e a n o p p o r t u n i t y t o r e a li s e su f f ic i e n t v a l u e a d d e d .

V a l u e a d d e d c a n b e c a l c u l a t e d i n c o s t b e n e f i t a n a l y s i s a t t h e g o i n g m a r k e t

p r i c e s. T h e f o l l o w i n g c o s t s a n d e x p e n d i t u r e s a r e r e l e v a n t : 6

- - c o s ts o f r e c u p e r a t i o n ;

- - c o s ts o f s e p a r a t e d g a r b a g e c o l l e c ti o n ;

t r e a t m e n t c o s t s o f r e s id u a l s ;

- - a v o i d e d c o st s o f w a s t e d u m p i n g ;

- - r e v e n u e s f r o m s e c o n d a r y m a t e ri al s.

C o s t s o f r e c u p e r a t i o n a r e c o s ts t h a t a r e m a d e t o u p g r a d e w a s t e m a t e ri a l fo r

f u r t h e r p r o c e s s i n g . I t c o v e r s t r a n s p o r t c o s t s , s t o r a g e c o s t s a n d p r i m a r y

t r e a t m e n t c o s ts . A v o i d e d c o s t s o f w a s t e d u m p i n g a r e th e c o s t s t h a t o t h e r w i s e

w o u l d b e m a d e f o r d i sp o s a l o f t h e w a s te t h r o u g h d u m p i n g o r i n c in e r a ti o n .

V a l u e a d d e d f o r r e c y c l i n g c a n b e c a l c u l a te d i n t h e f o l l o w i n g w a y: 7


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Recycling of lastics 2 5 5

V a l u e a d d e d = r e v e n u e s + a v o i d e d c o s t s o f w a s t e d u m p i n g - / - c o s ts o f

s e p a r a t e g a r b a g e c o l le c t io n - / - r e c u p e r a t i o n c o s ts - / - t r e a tm e n t co s t s o f

res idua ls .

D e p e n d i n g o n t h e s o u r c e , t y p e a n d q u a l i t y o f t h e w a s t e a n d t h e c o s t

s t r u c tu r e , t h i s ca l cu la t io n m ay l ead to p o s i t iv e v a lu e ad d ed o r n eg a t iv e v a lu e

ad d ed . F o r an a ly s in g th e p o ten t i a l v a lu e ad d ed , t h r ee ca t eg o r i e s o f wa s te can

b e d i s t in g ui sh ed : ( a ) was te th a t is p ro d u c ed b y p la s ti c m an u fac tu r e r s , ( b )

wa s te th a t is p ro d u ce d b y m an u fac tu r e r s o f p l a s ti c p ro d u c t s , an d ( c) wa s te

t h a t is p r o d u c e d b y t h e c o n s u m e r s o f p l as t ic p r o d u c t s . F o r t h e f ir st tw o

ca teg o r i e s , i n g en e ra l , p o s i t i v e v a lu e ad d ed can b e r ea l i sed . Was te i s u su a l ly

re leased a t s ing le loca t ions and in la rge quan t i t ies , thus reducing co l lec t ion

an d t r ea tm en t co s t s . Fo r th e th i rd ca t eg o ry , v a lu e ad d ed a t p r e sen t i s

g en e ra l ly n eg a tiv e . Th e wa s te is r e l ea sed in sm a l l q u an ti t ie s a t m an y d i f f e ren t

lo ca t io n s an d m ix ed wi th o th e r g a rb ag e . Co s t s f o r sep a ra t e co l l ec t io n a r e

h ig h . Th e sam e i s t r u e fo r sep a ra t io n a f t e r g a rb ag e co l l ec t io n (U .S . EPA,

1 9 9 0 ) .

4 T h e S t r u c tu r e o f t h e M o d e l

Th e m a te r ia l s b a l an ce o p t im isa t io n m o d e l i s d e s ig n ed o n th e b as i s o f t h e

cascad e d iag ram sh o wn in F ig . 2 . Th e s t r u c tu r e o f t h e m o d e l i s l a rg e ly

d e te rm in ed b y th e way in wh ich th e ca scad e fo r p l a s t i c s i s d e f in ed an d

e lab o ra t ed . Wi th th e q u a l i ty req u i r em en t s o f t h e u se r s an d th e ra t e o f

d eg rad a t io n an d p o l lu t io n o f th e m a te r i a l a s v a r i ab le s , we m ay d i sce rn th e

fo l lowing s tages in the casca de :

1 . v irgin app l ica t ions: app l ica t ion s fo r wh ich m ater ia l i s requ i red tha t has

n o t y e t b e e n u s e d . E x a m p l e s a r e p a c k i n g m a t e r i a l s f o r f o o d a n d d r i n k s

an d h ig h t ech ap p l i ca tio n s . Th e q u a l i ty s t an d a rd s o f t h e u se r s a r e

ref lec te d in the h igh qua l i ty o f the m ater ia l.

2 . H ig h s t an d a rd ap p l ica t io n s: ap p l i ca t io n s fo r wh ich th e u se o f f ir s t o rd e r

r eg ran u la t e i s r eq u i r ed . T h ese p ro d u c t s can a l so b e m a d e o f v i rg in

mater ia l . The regranu la te and the v i rg in mater ia l a re , in these app l ica-

t io n s , f u l l su b s t i tu t e s f o r each o th e r . Ex am p les a r e ap p l i ca t io n s fo r n o n -

foo d pack in g mater ia ls , fo i ls and p las t ic car par ts .

3 . Lo w s t an d a rd ap p l i ca t io n s: ap p l i ca t io n s fo r wh ich th e u se o f l o w q u a l i ty

regranu la te i s su f f ic ien t . The app l ica t ions a re o f ten fo r th icker p las t ics ,

wh ich m e an s th a t sm a l l d e f ec t s an d p o l lu t io n s o f t h e m a te r i a l a r e accep t -

ab le . Ex am p les a r e g a rd en fu rn i tu r e , p o le s f o r f en ces an d o th e r wo o d

rep lac ing app l ica t ions .

Th ese th r ee s t ag es a r e sh o wn in F ig . 3 , d em o n s t r a t in g th e m a in s t r u c tu r e o f

th e m o d e l . I n th e u p p e r p a r t o f t h e f ig u re , t h e p ro d u c t io n o f v i rg in m a te r i a l

takes p lace . Crude o i l i s conver ted in to raw mater ia l tha t , in i t s tu rn , i s

conver ted in to p las t ic g ranu la te . Next , the g ranu la te i s used in v i rg in app l ica-


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56 p F o l k e r t S t a rr e v e ld a n d E k k o C V a n I e r l a n d

2 ) ~ r o d u e g r o e y = l i ~

3 ~ ~ h i ~ ; a ~ v l r l ~ o ~

F ig 3 T h e m a i n s t r u c t u r e o f t h e m a t e r i a l s b a l a n c e o p t i m i s a t i o n m o d e l

t ions as wel l as in h igh s tandard app l ica t ions mid d le o f Fig . 3 ). H ow ev er ,

h igh qua l i ty app l ica t ions can a lso be made of h igh qua l i ty , recyc led mater ia l .

I n th i s ca se , co n se rv a t io n o f c ru d e o i l an d v i rg in m a te r i a l t ak es p l ace , wh i l e

th e was te is p ro p e r ly r ecy c led in s t ead o f in c in e r a t ed o r d u m p ed . H ig h q u a l i ty

w a s t e c a n b e o b t a i n e d f r o m p r o c e s s a n d p r o d u c t i o n w a s t e , p r o v i d e d t h a t t h e

m a te r i a l i s sep a ra t e ly co ll ec t ed . H ig h q u a l i ty was te can a l so b e o b ta in ed f ro m

p r o d u c t w a s t e , p r o v i d e d t h a t t h e m a t e r i a l i s c o l l e c t e d b y m e a n s o f d e p o s i t

sy s t em s , g u a ran tee in g th e p u ren e ss o f t h e co l l ec t ed was te . 8 H o w ev e r , ev en

th en , t h e was te s a r e o f t en p o l lu t ed b y r em a in in g fo o d d ep o s i t s e t c . wh ich

im p l i e s th a t t h i s k in d o f was te m a te r i a l sh o u ld b e c l ean ed in th e p ro cess o f

r e c u p e ra t i o n . A t y p ic a l e x a m p l e i s th e P E T - b o t t l e 9 f o r c o n s u m e r p r o d u c t s ,

u sed in sev e ra l co u n t r i e s in Eu ro p e . I t i s m ad e wi th a h a rd p l a s t i c wh ich i s

su i tab le fo r p ro du ct recyc l ing .

In th e lo wer p a r t o f F ig . 3 th e p ro cess in g o f lo w q u a l i ty ap p l i ca tio n s t ak es

p lace. Th ese ap p l i ca t io n s can b e m a d e o n th e b as i s o f m ix ed an d p o l lu t ed

was te m a te r i a l . Du r in g th e p ro cess o f r ecu p e ra t io n , t h e was te i s c l ean ed an d

u p g r a d e d t o r e g ra n u la t e. T h e r e g ra n u l a te c a n b e f u r th e r p r o c e s s e d b y m e a n s

of com pat ib i l i so rs , l ° in to low qual i ty app l ica t ions .

A n a l t e rn a t iv e way o f p ro cess in g m ix ed an d p o l lu t ed w as te is t h e rm a l

co n v e r s io n . Th e o b ta in ed r aw m a te r i a l c an ag a in b e u sed fo r th e f ab r i ca t io n

o f p l a st ic s . Th e m o d e l a l so co n ta in s th e o p t io n to u p g ra d e m ix ed w as te fo r

h ig h q u a l i ty ap p l i ca t io n s , Ho wev e r , i n th e p ro cess o f r ecu p e ra t io n th i s

r eq u i r e s co m p lex an d ex p en s iv e sep a ra t io n an d id en t i f i ca t io n t ech n iq u es .

Fina l ly , the m od el a l lows d i rec t p ro du ct recyc l ing . I f v i rg in and h igh qua l i ty

p ro d u c t s a r e co l l ec t ed , t h ey m ay b e u sed d i r ec t ly fo r t h e o r ig in a l p u rp o se ,

and in the c ase o f bo t t les , fo r exam ple , c lean ing and d is in fec t ion i s a

suf f ic ien t t rea tme nt .

5 T h e F u n c t io n i n g o f t h e M o d e l

Th e m o d e l i s a s t a t i c , s t ep -wise , l i n ea r o p t im isa t io n m o d e l . Th e d r iv in g fo r ce


7/14

Recycling o f Plastics 5 7

b e h i n d i t i s t h e d e m a n d f o r p l a s ti c a p p l ic a t i o n s c a t e g o r i s e d a s ( a) v i rg i n , ( b)

h i g h q u a l i t y a n d ( c ) l o w q u a l i t y a p p l i c a t i o n s . G i v e n t h e d e m a n d f o r t h e s e

p r o d u c t s ( D E M a , D E M b , D E M c ) , t h e p r i ce o f c r u d e o i l ( P oi l) , t h e co s ts a n d

t h e t e c h n i c a l c o n v e r s i o n p a r a m e t e r s ( r, s, t , u ) f o r t h e d i f f e r e n t p r o c e s s e s a n d

g a r b a g e c o l l e c t i o n s y s t e m s , t h e m o d e l c a l cu l a t e s t h e o p t i m a l w a y t o sa t is f y

d e m a n d . I n o t h e r w o r d s , th e m o d e l d e t e r m i n e s , b y m e a n s o f t h e o p t i m i s a t io n

p r o c e d u r e , w h i c h re c y c l i n g t e c h n o l o g i e s a n d g a r b a g e c o l l e c t io n s y s te m s

s h o u l d b e u s e d t o r e a c h t h e l o w e s t c o s t s o l u t i o n , f r o m a n o v e r a l l p o i n t o f

v i ew . T h e d e g r e e o f w a s t e p r e v e n t i o n , r e c y c l i n g ( hi g h q u a l i ty a n d l o w

q u a l it y ) , p r o d u c t r e c y c li n g , t h e r m a l c o n v e r s i o n a n d f i n a l ly , t h e d u m p i n g a n d

i n c i n e r a t i o n o f w a s t e , i s s i m u l t a n e o u s l y d e t e r m i n e d i n t h e o p t i m a l s o l u ti o n .

T h e o b j e c t iv e f u n c t i o n i s a s f o l l o w s P 1

M in (Poil * Xoil -t- C R A c

* X c r a

-1- P R O c * Xpro + FAB ~ i

* X f a b

JF

+ C O L c * X co + P R O R c * X pror + R E C c * X rec +

+ T H E R c * Xther + INC~ * Xin~ + D U M c * Xdum)

T h e m o s t i m p o r t a n t c o n s t r ai n t s a re :

(1)

X f a b l - - X p ro r 1 > D E M a

X f a b l -1 - X f a b2 - - X p r o r 2 > D E M b

X f a b l -~ - X f a b 2 ~- X f a b 3 - - X p r o r 3 > D E M c

X c o I = X d u m -1 - K i n c q -

( 1 / r

* X the r ) -1-

(1 /s * Xrec) + (1 / t

* X p r o r )

X f a b = U * X r e c

2 )

3 )

4 )

( 0 < r , s , t < 1 ) ( 5)

(0 < u < 1) (6)

w h e r e : P p r i c e

X q u a n t i t y

s u f f ix c co s t s f o r r e l ev a n t p ro ce s s

C R A c r ac k in g p r o c es s

P R O p r o d u c t i o n

F A B f a b r i c a t i o n

C O L c o l l e c t i o n

P R O R p r o d u c t r e cy c li ng

R E C r e c u p e r a t i o n

T H E R t h er m a l c o n v er s io n

I N C i n c i n e r a t i o n

D U M d u m p i n g

r , s, t , u c o n v e r s i o n p a r a m e t e r s f o r r e s p e c ti v e l y , t h e r m a l c o n v e r -

s i o n, r e c y c li n g , p r o d u c t r e c y c l in g a n d r e c u p e r a t i o n .


8/14

258 P. Folker t S tarreveM and E kk o L Van Ied and

To d e te rm in e th e e f f ec t iv en ess an d e f f ic i en cy o f th e v a r io u s p o l i cy in s tru -

m en t s f o r s t im u la t in g was te p r ev en t io n an d r ecy c l in g , we m ay im p o se ch a rg es

o n th e p r i ce s o f r aw m a te r ia l s , o n p ro cess e s an d o n ce r t a in p ro d u c t s . A l so we

can an a ly se th e e f f ec t s o f ch an g es in th e p r i ce s o f ce r t a in p ro cesse s o r

m a te r ia l s . I n th e ca se o f a ch a rg e o n th e u se o f vi rg in m a te ri a l, t h e p ro d u c t io n

co s t s a r e in c r eased th u s r ed u c in g th e p ro f i tab i l it y o f th i s p ro cess . Th e m o d e l ,

th ro u g h i ts o p t im isa t io n p ro ced u re , w ill sea r ch fo r a l t e rn a t iv e so lu t io n s to

m ee t th e d em an d fo r p l a s t i c s f o r t h e v a r io u s ca t eg o r i e s . I n th i s way th e

i m p a c t o f t h e p o l i c y m e a s u r e s o n t h e f u l l s y s t e m b e c o m e e v i d e n t . T h e

e f f ic i en cy o f th e p o l i cy m easu re s can b e e s t ab l i sh ed b y p lo t t in g th e e f f ec t o f

th e m easu re s ag a in s t t h e ad d i t io n a l su p p ly co s t s o f t h e p l a s t i c s . Th e co s t

e f fec t iveness o f the po l icy measures i s , therefore , es tab l i shed . In th is a r t ic le

we a r e fo cu ss in g o n sp ec i f i c ch a rges . O th e r p o ss ib l e p o l i cy in s t ru m en t s a r e

ch a rg es o n co l l ec tio n an d in c in e r a t io n o r a sy s t em o f d ep o s i t r e fu n d s o n

co n ta in e r s . Th e l a t t e r wo u ld p l ace th e co s t o f co l l ec t io n o n co n su m er s r a th e r

th an p ro d u ce r s . O th e r p o l i cy m e asu re s to b e an a ly zed a r e q u o ta s o n in c in e r -

a t io n o r d u m p i n g - - p e r h a p s s u p p o r t e d b y a s y s te m o f t r a d a b l e r ig h ts f o r

p las t ic d isposa l .

I n F ig . 3 , n o d i s t in c t io n i s m ad e b e tw een th e ty p es o f g ran u la t e an d th e ir

app l ica t ions . In the ac tua l model , we d iscern four types o f p las t ics , i . e .

p o ly e th y len e (PE) , p o ly p ro p y len e (PP) , p o ly v in y lch lo r id e (PVC) an d p o ly s ty -

r en e (PS). Th e se fo u r ty p es o f b u lk p o ly m er s a r e to g e th e r r e sp o n s ib le f o r

ab o u t 8 5 % o f th e to t a l v o lu m e o f p l a s t i c was te . Fo r th e ap p l i ca t io n s , we h av e

used four ca tegor ies : 1 . pack ing mater ia ls ; 2 . const ruc t ion mater ia ls ; 3 .

p l a s t i c s u sed in t r an sp o r t eq u ip m en t ; an d 4 . o th e r ap p l i ca t io n s (wh ich

inc lude , i n t e r a l i a , agr icu l tu ra l , domest ic app l ica t ions and tex t i les) . Basica l ly ,

each ca t eg o ry can m ak e u se o f t h e fo u r ty p es o f p l a s t i c s . Pack in g m a te r i a l s ,

f o r ex a m p l e , c a n b e m a d e o f P E , P P , P V C , a n d P S . I n p r ac t ic e h o w e v e r ,

p l a s ti c s a r e n o t p e r f ec t su b s t i tu t e s f o r each o th e r . Ea ch ty p e o f p l a s ti c h a s i ts

o wn ch a rac te r i s t i c s . A PET-b o t t l e , f o r ex am p le , i s co m p le te ly d i f f e r en t f r o m

a PVC-b o t t l e . Fo r th i s r ea so n , t h e m o d e l ac tu a l ly d i s t in g u i sh es 1 6 ty p es o f

ap p l ica t io n . W i th in each ap p l i ca t io n , t h e d i f f e ren t t y p es o f p l a s ti c can r ep lace

each o th e r p a r t i a l ly . Th e m o d e l d o es n o t y e t t ak e in to acco u n t th a t so m e

p ro d u c t s co n s i s t o f a co m b in a t io n o f d i f f e ren t t y p es o f p l a s ti c s ( l am ina tes ) . I n

t h e p r e s e n t v e r s i o n o f t h e m o d e l w e c o n s i d e r p r i v a t e c o s t s a u g m e n t e d w i t h

ch a rg es. I f p ro p e r e s t im a te s o f en v i ro n m en ta l d am ag e co s t s we re av a i lab le

th ese co u ld a l so b e in c lu d ed in th e m o d e l ca l cu la t io n s .

6 R e s u l t s

T h e m o d e l h a s b e e n u s e d t o c a lc u l at e t h e im p a c t o f a c h a rg e o n t h e d u m p i n g

an d in c in e r a tio n o f p l a s ti c was te s . Th e ca l cu la tio n s h av e b ee n ca r r i ed o u t b y

m ean s o f th e so f tware p ack ag e L I N D O . 12 In th e ca l cu la t io n s , t h e to t a l

d em an d fo r p l a s t i c i s t ak en f ro m th e Du tch s t a t i s t i c s f o r 1 9 8 6 , wh ich i s


9/14

Recycling of Plastics 259

considered to be the base year . The total demand is based on the actual

dem and for the categories of polymers PE, PP, PV C and PS. 13 The dem and

is specified according to the above mentioned categories of applicat ions. We

have assumed that the virgin applicat ions are mainly determined by the

demand for packing materia ls for food and refreshments , and the demand for

high-tech applicat ions. The demand for high quali ty applicat ions is by far the

largest (about 70 ) and m ainly consist s of the deman d for foi ls for non -foo d

applicat ions. Final ly, the demand for low quali ty applicat ions is determined

on the basis of the base year figures. These applicat ions amount to about 1

of the total dema nd and consist of applicat ions for garden furni ture, poles for

fences and road marking. The market for these applicat ions is, at present ,

still ve ry small.

We have used the fol lowing loss fract ions for the conversion coefficients:

in plast ic pro duc tion 1 , in plastic prod ucts fabricat ion 4 and in recup era-

t ion abo ut 10 . The price of crude oi l is est imated at abou t USS 20 per

barrel . Fo r d ump ing and incinerat ion of plast ics, the costs are est imated at

respect ively USS cents 2.5 and 9 per ki logram (USS 0.025 and 0.09, respec-

t ively). Final ly the costs of thermal conversion are est imated at USS 2.4 per

ki logram. If the quanti t ies are increased, these costs are increased step-wise

l inearly to USS 6.5 per ki logram, due to increasing costs per unit . The

est imation of the conversion factors and actual costs for the different pro-

cesses needs further analysis. However, i t is fel t that the figures used are

reasonable est imates of the relevant parameters. However, not al l actual cost

figures are avai lable in published stat ist ics and costs may change due to

technological progress.

On the basis of the presented input data , the model prod uces the base

case solut ion as presented in Fig. 4. In this solut ion the model chooses two

ways of recycling: materials recycling and product recycling. On the basis of

the presented input data that reflect , grosso modo actual market prices, the

Base case so lut ion

Incineration

60

umping

30

Fig. 4. The base case solution.


10/14

260 P Folkert Starreveld and Ekko C Yan Ierland

model calculates that about 10% of the total volume of plast ics waste is

recycled or re-used. It calculates that 60% should be incinerated and 30%

should be d um ped. A t the going prices, thermal conve rsion is not profi table.

We have carried out 11 optimisat ions to calculate the impact of a charge

on the price of dumping and incinerat ion. Apa rt f rom the base-case solut ion

we have calculated 10 optimisat ions, using increasing charges on dumping

and incinerat ion of plast ic wastes. By comparing the base-case solut ion and

the other solut ions we can establ ish the impact of the charge at different

levels. Figur e 5 gives the results o f the calculations.

Plastic waste 1000 ton)

0 0.05 0.1 0.15 0,2 0.25 0.3 0.35 0.4 0.45 0.5

Charge per kilogram

(in US )

] dumping ] incineration ] t h e r m c o n v e r s i o n

[ ~

mat.recycling ~ prod.recycling

Fig. 5. The impact of a charge on dumping and incineration.

The first remarkable resul t is that product recycling is preferred to

materials recycling. Thermal conversion is too expensive and is not used at

al l and is not st imulated by the charge. Secondly, i t becomes clear that the

charge should be rather high in order to have a substantial impact . For

example, i f we want to at tain about 25% of waste recycling and re-use, then

we have to charge abo ut US S0.30 pe r ki logram o f plast ic. Such a charge is

extremely high, in comparison with the costs of dumping and incinerat ion,

which amount to US S0.03 and 0.09 respect ively. The relat ive ineffect iveness

of the charge is due to the fact that the base-case solut ion already recycles

the (relat ively clean) process and production waste. This implies that recycl-

ing can only be increased by using product waste coming from households

and offices. This type of waste, however, is only suitable for recycling if

separa te was te col lect ion is taking p lace and at presen t this is very expensive.

The share of product and materials recycling is further specified in Figs. 6

and 7. Product recycling clearly identifies three steps. Without the charge,

only 3% of the used products are recycled. A charge of US S0.05 to US

S0.25 leads to 9% recycling. A charge of US S0.30 and more leads to

pro duc t recycling of abo ut 15%. The rather large steps that the mo del


11/14

Recycling of lastics

261

Product recycling

(1000 ton)

120 -1 : :

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Charge per kilogram in

US )

[ ]

Packing materials ~ Constr. materials [] Transport [ ] Others

Fig 6 The impact of the charge on product recycling

Material recycling

(1000 ton)

250

20 n 2

3

Charge per kilogram in

US )

[ ] rocess waste ~ roduction waste [] acking materials

V~ Cons t r .ma ter i a l s [ ] T ranspor t [ ]

Others

Fig 7 The impact of the charge on

materials

recycling

takes , can be explained by the fact that the mo del o nly includes a l imi ted

number of appl icat ions . I f a larger number of appl icat ions i s taken in to

acc oun t and i f mo re s tep-wise l inear re la t ionships are being used, then these

s teps wi ll autom at ical ly be co me smal ler.

The same analys is i s t rue for mater ia ls recycl ing. For a charge below US

0.35 re la t ively l i tt le impa ct c an b e n ot iced. O nly i f the pr ice o f v i rgin plast ic

granulate r i ses to the level of the pr ice of regranulate (obtained af ter

recycling) , can we ex pect ma nufa cture rs to shi f t towa rds the process ing o f

regranulate . Par t icular ly the product ion of regranulate on the bas is of

packing mater ia ls wi l l be s t rongly s timulated.

The e f f ic i ency o f the charge on dum ping and inc inera t ion is shown in F ig.

8 . The cos ts that are shown are excluding the charges that are t ransfer red to


12/14

262

P Folkert Starreveld and Ek ko C Van ieHand

Total costs

(Bil l ion US )

0.6

0 . 5 . . . . . . .

0 4 . . . . . . . .

0 . 3

j~

J

0 2 . . . . .

J

/

i J

0.1L ~ j o ~ j ~

. . . .

0 ~ i i r i

10 20 30 40 50 60 70

l te rnat ive t reatment (in %)

60 90 1O

Fig 8 The costs of a l ternat ive opt ions for p las t ic waste t rea tment

the public authorities and finally reimbursed to the manufacturing sector.

Figure 8 clearly shows that the costs of alternative ways of processing show

an upward sloping pattern. It reveals that the first tonnes of material can be

recycled at relatively low costs. Increasing quantities can only be recycled at

higher costs per unit.

The model also makes it possible to calculate the impact of other policy

measures. A comparison of the effects of the different policy measures can

identify the most effective ones in decreasing the quantity of plastic waste

being dumped or incinerated.

7. Conclusions

The aim of the analysis was to construct a materials balance optimisation

model for the recycling of plastics in order to establish the effectiveness and

efficiency of various policy instruments to stimulate the recycling of plastics.

The effectiveness is established by calculating the impact of a charge on the

dumping and incineration of plastic waste. The calculations show that we

need a rather high charge as compared to the actual cost of dumping and

incineration to obtain significant results for the quantity of recycling. The

calculations show that product recycling is preferable to materials recycling.

The model in its present state is rather sensitive to small changes in the

charges. This is due to the fact that the model includes only a limited number

of plastic applications and that only one step-wise linear cost function is

applied. Introducing adjustments in this regard will make the model more

realistic and less sensitive leading to a more natural reaction pattern.

Concerning the efficiency of the policy measures the model shows the

total system costs for the different options thus revealing the additional cost

per unit of reducing dumping and incinerating.


13/14

Recycling of Plastics

2 6 3

T h e a n a ly s is c a n b e i m p r o v e d i n a n u m b e r o f w a y s . F i rs t th e d a t a a n d t h e

v a lu e s o f t h e p a r a m e t e r s c o u l d b e m o r e c a re f u ll y s tu d ie d . M o r e i m p o r t a n t

h o w e v e r is th e d y n a m i s a t i o n o f t h e m o d e l a n d t h e i n t r o d u c t i o n o f t e c h n ic a l

p r o g r e s s , a l so f o r n e w a p p l i c a t io n s o f r e c y c l e d m a t e ri a l. I n th e p r e s e n t

r e s e a r c h p r o j e c t w e l i m i t e d o u r s e l v e s t o a ( s t e p w i s e ) l i n e a r s t a t i c a n a l y s i s .

A n a l te r n a t iv e w o u l d b e t o u s e c o m p a r a t i v e s ta ti c an a l y si s f o r c h a n g e s i n

p a r a m e t e r s a n d e x o g e n o u s v a r ia b l e s. H o w e v e r , t h e a n a l ys i s c o u l d a l so b e s e t

i n a d y n a m i c c o n t e x t, f u r t h e r a n a l y s i n g t h e c o n t i n u o u s l y g r o w i n g m a r k e t f o r

p l a s t ic s a n d r e c y c l e d p l a st ic s . I n t h is w a y , a d y n a m i c s c e n a r i o s t u d y f o r

p l a st ic r e c y c l i n g c o u l d b e c a r r i e d o u t . T h e m o d e l w o u l d t h e n m a k e i t p o s s i b l e

t o a n s w e r t h e q u e s t i o n w h e t h e r , i n d e e d , i t w i ll b e p o s s i b l e t o r e a c h t h e

t a r g et s f o r p l a s ti c r e c y c l i n g f o r t h e y e a r 2 0 0 0 , a s s p e c if i ed b y t h e p u b l i c

a u t h o r it ie s . A l s o , it c o u l d p r o v i d e m o r e d e t a i l e d a n s w e r s a b o u t w h i c h p o l i c y

m e a s u r e s s h o u l d b e t a k e n t o r e a c h t h e s p e c i f ie d g o a ls .

cknowl edgement s

T h e a u t ho r s k i n d ly a c k n o w l e d g e t h e u s ef u l c o m m e n t s o f tw o a n o n y m o u s

r e v i e w e r s o n a p r e v i o u s v e r s i o n .

Not e s

O EC D , Hou seho ld waste, separate collection and recycling, Paris 1983.

2 See for example Curlee, T. R., The economic feasibili ty of recycling: a case study of plastic

wastes, Prea ger Publishers, New Y ork, 1986.

3 See Van Weenen, H., Waste prevention: theory and practice. Pallas Offset BV, The Hague,

1990.

4 Rec upe ration refers to the processing of waste to m ake it suitable fo r re-use. In general

it consists of the following stages: transport, separation, shredding, agglom eration and

purification.

Mo rn, A. J. A., Environmental technology for recycling 19 91 --1 99 4 (in Dutch). Civ i

Consultancy, Leidschendam, 1991.

6 See for example E . Doekem eijer and E. C. van Ierland, Recycling of domestic w aste (in

Dutch), E con om isch Statistische Berichten, 2 (1987), pp. 16 6- - 168.

7 See Glenn, J., Recycling Econ om ics Benefit-Cost Analysis. BioCycle.

s It is assumed that a pro du ct contains only a single plastic and is not a composite product.

9 P E T means polyethyleneterephtalate.

i0 C°m patibilizers ma ke °ne ldnd ° f plastic c°mp atible with an°ther

~ C R Ac, PROc, FA Bc, etc. are the costs pe r unit process-output. X . . . X p r o Xfab, etc . are the

amounts of output,

,2 L IN D O , Linear, Interactive, and Discrete Optimizer. Erasmus U niversity, R otterd am 1983.

~3 Kremers G. and R van O oye n, The m arket fo r plastics in the Netherlands (in Dutch).

unststofen rubber(1988), nr. 11, pp. 14--25.


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L o n d o n .

Curlee, T. R. (1986), The Ec on om ic Feasibil ity o f Recycling. A Case Study o f Plastic Wastes ,

Preager Pub l i she rs , New York .

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recycling of plastics_a materials balance optimisation model.pdf

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