a system approach to municiple solid waste management - a pilot study of goteborg

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Waste Management & Research (1994) 12, 73-91

A SYSTEMS APPROACH TO MUNICIPAL SOLID WASTE

MANAGEMENT: A PILOT STUDY OF GOTEBORG

J. Sundberg, P. Gipperth and C.-O. Wene

Energy Systems Technology Division, Department of Energy Conversion, Chalmers University ofTechnology, S-412 96 Gb'teborg, Sweden

(Received 13 June 1992, accepted 13 January 1993)

T h e p r o p o se d sy s te m s a p p r o a c h t o solid w a s t e m a n a g e m e n t c o n si st s o f tw o p a r t s ,

f i r s t , a comprehens ive mode l , MIMES/WASTE (a Mode l fo r desc r ip t ion andopt imiza t ion of In tegra ted Mate r i a l f lows and Energy Sys tems) , fo r ana lys ing thetechnica l p roper t i e s o f the was te management sys tem, and second , p rocedures tomake the model into an eff ic ient tool in the planning process. The paper focuses onthe f i r s t pa r t by desc r ib ing the mode l and the me thodology for us ing i t fo r b roadscope t echn ica l ana lys i s o f the was te management sys tem. A p i lo t s tudy fo r theG6 tebo rg reg ion in Sweden , i l l us tra t ing the m e thod ology and the use o f the mo de l , isp resen ted . The MIMES/WASTE mode l i s a sys tems eng inee r ing too l fo r s t ra t eg icp l a n n in g o f m u n i c ip a l w a s t e m a n a g e m e n t sy st em s . T h e m o d e l p r o v id e s a f r a m e w o r kfor consistent evalua t ion of : (i ) a large num be r of feasible op t ions for developin g thesystem, ( i i ) the effects of uncer ta int ies in the system environment and, ( i i i ) var ious

goals se t up for the system (e .g . cost efficiency, env iron m ental c ontro l , recycl ing, andenergy produc t ion) . T hree m odes o f app l i ca tion a re d iscussed : long- te rm p lann ing ;shor t - t e rm p lann ing ; and consequ ence ana lysi s .

Key W or ds - -W as te m anage m ent , munic ipa l sol id w as te , sys tems ana lysi s , mun ic ipa lengineer ing, mathemat ica l models , cost effec t iveness, in tegra ted re-source p lann ing , emiss ions con t ro l .

1. Introduction

P r e s e n t - d a y r e g i o n a l a n d m u n i c i p a l s o l i d w a s t e m a n a g e m e n t i n v o l v e s p l a n n i n g p r o b -

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

e n v i r o n m e n t a l p r o b l e m s h a s f o r c e d g o v e r n m e n t s , l o c al a u t h o r it i es a n d u ti li ti es f o r w a s t e

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

m a n a g e m e n t s y s t e m s .

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

s o o n b e f il le d a n d e x i s ti n g i n c i n e r a t i o n p l a n t s , i f a n y , a r e a l r e a d y f u ll y u se d . N e w

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

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

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

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

n e w s p a p e r , g l a s s , a l u m i n i u m c a n s , e t c .

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

y e a r s in t h e le a d i n g i n d u s t r ia l c o u n t r i e s , w i t h t h e a i m s o f e n c o u r a g i n g r e d u c t i o n o f th e

w a s t e p r o d u c e d a n d i n c re a s in g r e u se a n d r e c y c li n g o f w a s t e c o m p o n e n t s . H o w e v e r , m o s t

o f th e s e e f f o r ts h a v e b e e n f o c u s e d o n h a z a r d o u s w a s t e s , w h i l e th e l a r g e w a s t e s t r e a m s o f

m u n i c i p a l s o l i d w a s t e , M S W ( i . e . h o u s e h o l d w a s t e , i n d u s t r i a l w a s t e , c o n s t r u c t i o n a n d

d e m o l i t io n w a s t e a n d s e w a g e s lu d g e ), a r e h a n d l e d in m u c h t h e s a m e w a y a s b e f o r e .

0734-242X/94/010073 + 19 $08.00/0 © 1994 ISW A



74 J. Sundberg et al.

The new regulations for waste management in Sweden, approved in May 1990, by the

Swedish parliament include the following (The Swedish Association for Solid Waste

Management, 1990):

• From January 1991 every municipality in Sweden is obliged to draw up a solidwaste plan for the handling of all wastes produced in the municipality. Priority shall

be given to: (i) reducing the quantity of waste produced; (ii) encouraging reuse and,

(iii) encouraging recycling.

• Source separation (by households and industries) should be developed in such a

way that:

(1) From 1994 all wastes delivered for final treatment are separated into categories

suitable for proper handling.

(2) Incineration and landfilling of unseparated waste will cease almost completely

by the end of 1993. Methane gas from landfilling shall be recovered for energyuse, or flared.

Several changes throughout the waste management system, in both technology and

organization, are necessary to develop systems that fulfill these new demands. There is

an obvious need for tools for broad scope analysis of the waste management system, not

only for the task of finding environmentally acceptable cost efficient solutions for the

technical system, but also for the task of initiating a learning process (Checkland 1981)

for the actors in the waste management system.

This paper describes a model and a method that takes a systems approach to the

management of regional/municipal solid waste. The systems approach consists of twoparts: (1) a comprehensive model for analysing the technical properties of the system;

and (2) procedures for model use by the system actors. The application of a systems

engineering model to initiate a learning process among the system actors is discussed, for

example, by Wene & Ryd~n (1988).

The concentration here is on the technical analysis, i.e. the first part of the systems

approach. There is a description of the general properties of the Waste Management

System (WAMS) and a model (MIMES/WASTE)* that can be used for broad scope

technical analysis of the system. The type of results that can be obtained from the model

is also explained. MIMES/WASTE is developed from a general model for linked energyand material flows (Sundberg & Wene 1988; Sundberg 1989).

The MIMES/WASTE model has been designed for the integrated analysis of:

Strategies for source separation;

Options for recycling;

Technical options for processing of solid waste;

Sales to the energy and material markets; and

Options for reducing pollutants and emissions resulting from WAMS.

Previous models for the analysis of solid waste management systems are brieflydiscussed and compared in Gottinger (1988) and Liebman (1975). In the late 1960s and

in the 1970s, several model approaches were presented. Most of these models focus on

subsystems of WAMS. One of the most common subsystems in these model studies is the

transport system, where models are used for vehicle routing optimization.

Today, models have to handle more complex systems in order to face present changes

in solid waste management. Some interesting more recent approaches are the RRPLAN-

model (Chapman & Berman 1983) and the HARBINGER-model (Rushbrook 1987).

* MIMES: a Model for description and optimization of Integrated Material flowsand Energy Systems



Municipal solid waste management 75

The RRPLAN model is developed to handle several planning problems of the regional

waste management system. It has a wide scope with a system boundary similar to

MIMES/WASTE which permits integrated analysis of options and strategies in WAMS.

However, in comparison with MIMES/WASTE, RRPLAN uses a simpler description

for waste streams and processing equipment. Emissions are not included. An advantage

of RRPLAN is the option to use declining prices and limited size markets for the

material recovery. This option has not yet been studied for MIMES/WASTE.

Another general model that also has a wide scope, similar to the one above, is the

HARBINGER model. This model is made up of eight sub-models. Six of them are used

to prepare inputs and two for analysing different strategies. Since no time-based

optimization routines are used in the model, strategies have to be compared and

analysed through several simulations. Also, the waste streams are limited by the number

of component fractions that can be considered, and this reduces the capacity of the

model for analysis of source separation and its impact on emissions in downstream

processes. An option that is not available in MIMES/WASTE is the detailed analysis of

the transport system that is in the transport network sub-model. This sub-model derives

the shortest times through the road system for the waste collecting vehicles.

The MIMES/WASTE model has been used in two pilot studies, one of the G6teborg

region (700,000 inhabitants) by Gipperth & Sundberg (1990), and one of the municipality

Bor~s (100,000 inhabitants) by Bergqvist & Carlsson (1988). The pilot study of G6teborg

is presented in this paper. A larger and more detailed study of the G6teborg region has

recently been started together with some of the major actors in the regional system.

The following section describes the general modelling principles and the methodology

and modes of application. Section 3 describes the MIMES/WASTE model and how the

model couples the material and energy flows. Finally, a pilot study of the G6teborg

region is presented. The aim here is to illustrate how the model can be used and what

types of results it provides.

2 . Methodo logy

2 .1 T h e b o un d a r ie s o f th e w a s t e m a n a g e m e n t s y s t e m

Figure 1 indicates the most important factors in the environment of the Waste

Management System (WAMS).

WAMS is an open system that exchanges energy, material and information with its

environment, across the system boundaries. It is important to identify an efficient system

boundary that fits the defined problem and where possible, to study the interactions

between the system and its environment through a limited set of environmental factors.

With the boundaries chosen here, one can identify seven important factors in the

WAMS environment:

(i) The quantity and mixture of incoming waste and the degree of source separation.

In the present application, the upstream boundary is set at the point of output

waste flows from households and industries.

(2) The demand for recycled materials on the markets.

(3) The availability of new sites for landfills.

(4) The demand and wholesale prices for electricity and low temperature heat for

district heating.

(5) The price and availability of auxiliary energy supply, e.g. oil, electricity, diesel etc.



76 J . S u n d b e rg et al.

Technologydevelopment

Energyma r ke t s

O E lectr ic i ty

O Fuel I trsp}

0 Oil - I

Waste

0 Sources

O Quant i ty

o MixtureO Source separa t ion

W A S T EMA N A G E ME N T

SYSTEM

/Mater ia lMarke ts

0 Paper

O Meta ls

O Compost

O Glass, etc

\ \/ / / / / /

Landfill

E nv i r onme n ta lrestr ic t ions

~ EnergyMarke ts

O Electr ic i ty

/ I 0 Distr icthea t ing

0 Biogas, etc

> E m i s s i o n s ,

dra inage

Fig. 1. The environm ent of the waste managem ent system.

( 6 ) E n v i r o n m e n t a l r e s t r i c t i o n s , e . g . o n e m i s s i o n s f r o m i n c i n e r a t i o n a n d o n d r a i n a g e

f r om l a nd f i l l s .

( 7 ) A v a i l a b i l i t y , c o s t a n d t e c h n i c a l p r o p e r t i e s o f n e w t e c h n o l o g i e s .

T h e b o u n d a r y o f W A M S , a s d e s c r i b e d a b o v e , i s n o t f i x e d , d u e t o m e t h o d o r m o d e l

l i m i ta t io n s . D e p e n d i n g o n t h e n a t u r e o f t h e p r o b l e m i n v e s t ig a t e d , a w i d e r o r a n a r r o w e r

s y st em c a n b e u se d f o r W A M S a n d h a n d l e d b y t h e c o m p u t e r m o d e l , i f p r e fe r re d . F o r i n st an c e ,

M I M E S / W A S T E h a s a l re a d y b e e n u s e d in lo n g i t u d i n a l s t u d i es o f s p ec if ic w a s t e s tr e a m s .

2 . 2 T h e m o d e l a s a p l a n n i n g i n s t r u m e n t

T h e M I M E S / W A S T E m o d e l is a o n e ti m e - s t e p m o d e l . I t is d e s i g n e d t o fa c i li ta t e f in d i n g

n e w s o l u t i o n s f o r f u t u r e w a s t e m a n a g e m e n t s y s t e m s t h a t a r e c o s t ef fi ci en t a n d e n v i r o n -

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

t h a t a r e s u g g e s te d f o r t h e s y s t e m o r o f p r o p o s e d w a s t e m a n a g e m e n t p l an s .

T h e t h re e m o d e s o f m o d e l a p p l i ca t io n s a r e l o n g - te r m p l a n n in g , s h o r t - t e rm p l a n n i n g

a n d c o n s e q u e n c e a n a ly s is . T h e m o d e s c a n b e us e d i n d e p e n d e n t l y o r i n c o m b i n a t i o n , f o r

t h e a b o v e m e n t i o n e d p u r p o s e s . T h e d i f fe r e n c es b e t w e e n t h e m o d e s a r e s h o w n i n T a b l e 1.

F o r l o n g - t e r m p l a n n i n g , s y s t em s t u d i es a r e p e r f o r m e d b y s c e n a r i o a n a ly s i s in o r d e r t o

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

" o p t i m a l s o l u t i o n " f o r t h e f u t u re W A M S b u t s e v e ra l o p t im a l s o l u ti o n s f o r d if fe r en t

b o u n d a r y c o n d i t i o n s , e a c h an s w e r in g q u e s ti o n s o f a " w h a t i f . . . ? " c h a r a c te r . T o g e t h e r ,



M u n i c i p a l s o l i d w a s t e m a n a g e m e n t

TABLE I

M o d e l modes

77

Modelling

Model modes technique Objective Options

Long-term planning

Short-term planning

Consequence analysis

Optimization Minimumsystem cost Flows and process*(LP/NLP) (variableand fixed costs)

Optimization Minimumsystem cost Flows*(LP/NLP) (variablecosts only)

NoneSimulation NA Flows and processest

* Internally controlled by the system objective.

t Externally introduced by the modeller. LP, linear programming. NLP, non-linear programming.

Options: Alternatives to the existing system (flows and processes) that can be included.Flows: All flows of both energy and materials can be optional by both rate and route.

Processes: New processes (technology) may be used. When they are used, investments or re-investments are

included.NA, Nol applicable.

these solutions are used to form a strategy for the development of the system. Examples

of long-term planning problems that can be analysed by the model are:

Introduction of new technology (e.g. bio-gas plants, composting plants);

Introduction of emission fees and differentiated waste fees;

Options for heat and/or electricity production;

Strategies for source separation.

In the next mode, short-term planning, the new investments option is excluded. This

mode describes how the waste streams of WAMS should be utilized using existing

technology in order to minimize costs. For example, at what price for recycled newsprint

does burning become a cost efficient option? What fees should be used for construction

waste, if the combustible fractions are separated at the construction sites?

The difference between consequence analysis and the other two modes is that the use

of processes and flows are fixed, instead of being a result of the optimization. This mode

shows whether given assumptions for the system inputs (input waste, separation,

restrictions etc.) are feasible and, if so, what consequences these assumptions have for

waste flows and emissions in downstream processes. This mode can be used to evaluate a

proposed plan from the viewpoints of technical, economic and environmental feasibility,

or to calculate certain variables, for instance, the total amount of nitrogen oxides that is

emitted from the system.

3 . T h e m o d e l

The systems approach to municipal waste management, described in this paper, is built on

the modelling concept of MIMES. MIMES offers a general concept for modelling large

and complex systems of both material and energy flows, i.e. methods for systems

identification and representation, model formulation, systems optimization and simula-

tion. The model is generic, applicable to different kinds of systems and problems

(Sundberg 1989). For the analysis of waste management systems the modelling concept is




Choice of varietySelection of mathem atical

solution techniqu e

REMS

Graphicrepresentation

SYSTEM

I DEVICES I[ E Q U A T I O N S t A LG OR IT HMComponen t ] M at h em at ic a l So lu tionI descriptions representation method

lf I + o , + + + pFig. 2. The general structure of the M IMES modelling concept.

d e n o t e d M I M E S / W A S T E . T h e e x t e n s i o n W A S T E r e f e r s t o t h e m e t h o d o l o g i c a l a s p e c t s

d iscussed in the previous sect ion and the ready-bui l t s t ructure for graphic representa t ions

and c om pon en t desc r ip tions , wh ich is fu r the r desc ribed under "cho ice o f va r ie ty" be low .

The m ode l l ing concep t , a s i llu s t ra ted in F ig . 2 , cons i s t s o f two m ajo r s t eps . A genera l

d i s cus s ion o f the tw o-s tep p roces s o f mode l b u i ld ing i s foun d in Wen e (1989). T he f ir s t

s t ep , he re named '+cho ice o f va r ie ty" , dea l s w i th the p rob lem o f how sys tems shou ld be

rep resen ted in the mode l . The t a sk in th i s pa r t is to s e lec t va lua b le in fo rm at ion f rom the

real sys tem and to descr ibe i t in the model , i . e . to ident i fy an ef f ic ient sys tem boundaryand to de f ine wh ich t echno log ies and f lows shou ld be inc luded in the s tudy , a s we ll a s to

dec ide the l eve l o f aggrega t ion fo r the s tudy . Moreover , the coup l ing o f f lows in the

p roces ses i s de f ined he re . F rom a use r ' s v iew , th i s is the pa r t wh ere m os t w ork i s done .

T h e s e c o n d p a r t o f t h e m o d e l , n a m e d " s e l e c ti o n o f m a t h e m a t i c a l s o l u t i o n t e c h -

n i q u e s " , c o n c e r n s th e m a t h e m a t i c a l r e p r e s e n t a ti o n o f th e s y st e m a n d t h e m e t h o d s u s e d

to f ind d i f f e ren t types o f so lu t ions to these r ep resen ta t ions . The mathemat ica l rou t ines

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

F o l l o w i n g t h e m o d e l l i n g s t r u c t u r e s h o w n i n F i g . 2 , t h e p a r t s o f M I M E S a r e b r i e f l y

desc r ibed be low:

3 .1 S.vslem

The model i s des igned for sys tems of l inked energy and mater ia l f lows , of which the

W A M S is a typical exam ple . Ac cordingly , i t is no t l imi ted by a specif ic sys tem or b y

specif ic technologies . Two impor tant fac tors that make th is poss ib le are : ( i ) a general

f ram ew ork for techn olog y descr ip t ions , and ( i i) f lex ib le aggrega t ion levels for m odel units.

3 . 2 R E M S

A graph ic r ep resen ta t ion o f the sys tem mode l led i s neces sa ry fo r hand l ing the com-

p lex ity o f l arge sys tem s in a com prehe ns ive w ay . In energy sys tem s eng ineer ing , ne tw ork

d iag rams a re used to show the f low o f energy ca r r i e r s f rom energy sources v ia energy

conver s ion t echno log ies to the f ina l consumer . The d iag rams a re ca l l ed Refe rence

Energy Sys tems (RES) . Th is t echn ique has been deve loped to r ep resen t l inked energy

a n d m a t e ri a l f l o w s i n R e f e r e n c e E n e r g y a n d M a t e r ia l S y s t e m s ( R E M S ) . A n e x a m p l e o f a

R E M S d i a g r a m f o r w a s t e m a n a g e m e n t is f o u n d i n s e c ti o n 4 . T h e g r a p h i c r e p r e s e n t a t io n




(a) +-

E ,~

E+.

+ o l +

~ ~.

DEVICE

~. E~

E ;.

E ;

(b)

i

M+!

(c)

'

Fig. 3. (a) Input and output flows, (b) material flows through a device, (c) energy flows through a device.M, Material flow; E, energy flow; H, enthalpy flow; +, input flow; - , output flow.

identifies the system boundaries, and defines the scope and detail of the technical

analysis of the system. It is also an important tool for evaluating the model results

together with the actors in the system.

3 .3 D e v ic e s

The devices in MIMES are the nodes in the network of energy and material flows. They

represent technical equipment or subsystems for the treatment of energy and/or material

flows. They are treated as "black boxes" and are described, accordingly by the relations

between input and output flows. MIMES offers a set of device options and flow options

for the device descriptions. These options define: (i) possible flow paths through the

device, (ii) the relations between flows, and (iii) the control of flows.

Figure 3(a) shows how a device is illustrated in the REMS flow diagram with material

flows shown vertically and energy flows horizontally. Figures 3(b) and (c) illustrate the

possible directions for material and energy flows. The coupling between all these flows is

defined by the device and flow options, as mentioned above. A purpose-built program,

DEVED, can be used for designing devices for MIMES (Sundberg 1989).

3 . 4 E q u a t i o n s

The equation part of the MIMES modelling concept consists of a set of generic

equations, linear and non-linear. The REMS and device analysis provide the basis for

selecting and specifying equations to obtain an algebraic representation of the system.

The selection and specification of equations can be formalized through the DEVED

program. The system of equations is solved by the following algorithm.

3 . 5 A l g o r i t h m

For the mathematical optimization and simulation, MIMES uses non-linear program-

ming (NLP) and linear programming (LP) algorithms. The main option is NLP. Since

some systems may be described and modelled by purely linear equations, the option to

use standard LP algorithms is available. From a mathematical point of view, linear



80 J . S u n d b e r g et al.

e q u a t i o n s y s t e m s a r e t o b e p r e f e r r e d . T h e m a i n a d v a n t a g e s o f u s i n g L P a r e t h e e a s e o f

h a n d l i n g l a r g e e q u a t i o n s y s t e m s a n d t h e s p e e d i n s o l v i n g t h e m . H o w e v e r , n o n - l i n e a r

e q u a t i o n s m u s t b e u se d f o r th e a p p li c a ti o n s o n W A M S . I n th e p i lo t s t u d y o f G 6 t e b o r g ,

3 0 o u t o f a t o ta l o f 1 10 0 e q u a t i o n s a r e n o n - l i n e a r . I n M I M E S , o p t i m i z a t i o n a n d

s i m u l a t i o n a r e h a n d l e d b y t h e p r o g r a m m i n g p a c k a g e G A M S ( B r o o k e e t a l . 1988) .*

T h e c o m p u t e r i m p l e m e n t a t i o n o f M I M E S i s w r i t t e n f o r P C - 3 8 6 / 4 8 6 m a c h i n e s

r u n n i n g u n d e r D O S . P r o b l e m s p r o d u c e d a n d s o l v ed w it h M I M E S a re s h o w n t o b e b o t h

e a s y a n d f a s t t o s o l v e o n s u c h a s y s t e m .

F o r a d e t a i le d d e s c r i p t io n o f t h e m o d e l a p p r o a c h a n d t h e m o d e l d e si g n o f M I M E S t h e

r e a d e r i s r e f e r r e d t o S u n d b e r g ( 1 9 8 9 ) .

4 . E x a m pl e s f r o m a p i lo t s t udy

T h e p i lo t s tu d y o f t h e w a st e m a n a g e m e n t s y st em f o r th e r eg i o n o f G 6 t e b o r g w a s

c o n d u c t e d i n c o o p e r a t i o n w i t h t h e r e g i o n a l w a s t e m a n a g e m e n t e n t e r p r i s e ( G R A A B ) .

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

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

c o n s t r u c t io n a n d d e m o l i t i o n w a st e. N e w t e ch n o l o g ie s f o r t h e c o m p o s t a b l e c o m p o n e n t s ,

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

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

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

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

G 6 t e b o r g . T h e M I M E S / W A S T E m o d e l w as u se d to o p ti m i z e t he s y st em . O p t i m i z a t i o n s

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

N O , e m i s s i o n f ee s, a n d t o t a l a m o u n t o f w a s t e t o b e p r o c e s s e d .

4 . 1 T h e p r e s e n t s i t u a t i o n

T h e r e a r e n i n e c o m r n u n i t i e s w i t h i n t h e G 6 t e b o r g r e g i o n w i t h a t o t a l o f 7 0 0 , 0 0 0

i n h a b i t a n t s , c o v e r i n g a n a r e a o f 25 0 0 k m-'. G 6 t e b o r g is t h e l a r g es t c o m m u n i t y w i t h

4 0 0 , 0 0 0 i n h a b i t a n t s . T h e r e g i o n a l w a s t e m a n a g e m e n t e n t e r p r i s e , G R A A B , i s o w n e d

j o i n t l y b y a l l th e c o m m u n i t i e s .

T h e G R A A B e n t e rp r i se h a n d l es m o s t o f t h e d o w n s t r e a m o p e r a t i o n s f o r so li d w a st e,

s u c h a s i n c i n e r a t i o n a n d l a n d f i l l . W i t h i n t h e c o m m u n i t i e s , t h e l o c a l a u t h o r i t i e s a r e

r e s p o n s ib l e f o r t h e c o l l e c ti o n o f so li d w a s t e f r o m h o u s e h o l d s , c o m m e r c i a l a n d i n d u s t r ia l

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

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

o p e ra te d b y G R A A B .

T h e i n c i n e r a t i o n h e a t a n d p o w e r p l a n t , j u s t o u t s i d e G 6 t e b o r g , i s t h e m a i n f a c i l i t y i n

t h e s y s te m . T h e p l a n t p r o c e s s e s 3 0 0 , 00 0 t o n n e s o f s o l id w a s t e a n n u a l l y . U p t o 8 0 , 0 0 0

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

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

s t ab l e h e a t i n g v a l u e a n d a l o w e r c o n t e n t o f h e a v y m e t a ls .

A t p r e s en t , t h e i n c i n e r a t io n p l a n t d e l iv e r s a b o u t 7 0 0 G W h / y o f h e a t t o t h e d i s tr i ct

h e a t i n g s y s t e m , w h i c h is o p e r a t e d b y G 6 t e b o r g E n e r g i . I n 1 99 0, t h is w a s 2 0 % o f th e t o t a l

h e a t r e q u i r e d b y t h e d i st r ic t h e a t i n g s y s t em . T h e p l a n t p r o d u c e s 9 0 G W h / a o f e l e ct ri c it y ,

* GAM S (G eneral Algebraic Mo delling System): A mathem atical framew ork for op timization that includesmatrix generation and a set of optimization algorithms. The m ain solve r us ed for M IME S is theNLP-algorithm MINO S (Brooke et ol. 1988).




o f w h i c h 5 0 G W h is s o ld a n d 4 0 G W h is c o n s u m e d i n t e r n a ll y . In 1 98 9, a f lu e -g a s

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

m e t a l s , d u s t a n d d i o x i n s . B y u s i n g t h e l a t e n t h e a t i n c o n d e n s i n g v a p o u r , t h e c l e a n i n g

s y s t e m i n c r e a s e s t h e e n e r g y y i e l d f r o m t h e w a s t e b y 2 5 % .

T h e R E M S f lo w d i a g r a m i n F ig . 4 g iv e s f u r t h e r d e t ai l s o n t h e r e g i o n a l w a s t e

m a n a g e m e n t s y s t em . T h e v e r ti c a l l in e s d e n o t e w a s t e f lo w s a n d t h e y a r e d e s c ri b e d i n t h e

m o d e l a s m a s s f lo w s w i t h a s pe c if ic e n e r g y c o n t e n t . H o r i z o n t a l a r r o w s t o a n d f r o m a b o x

d e n o t e e n e r g y f lo w s , f o r e x a m p l e f u e l r e q u i r e m e n t s f o r t r a n s p o r t . T h e m a s s f l o w s s h o w n

i n th e f i g u r e a r e d e s c r i b e d i n t h e m o d e l b y u p t o 15 v a r i a b l e s , e a c h r e p r e s e n t i n g a s p e c if i c

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

u p p e r p a r t o f F i g . 4 a n d i n T a b l e 3 .

T h e R E M S d i a g r a m i n d ic a te s t h a t t h e re is s o m e s e p a r a t i o n i n t o w a s te c o m p o n e n t s a t

t he h o u s e h o l d s ( " S . S E P " ) . O f t h e t o ta l a m o u n t o f p a p e r a n d g la ss h a n d l e d b y t h e

s y s t e m , 6 7 % a n d 3 2 % , r e s p e c t i v e l y , a r e s e p a r a t e d a t s o u r c e a n d s o l d o n t h e m a r k e t f o r

r e c y c le d p r o d u c t s . A t p r e s e n t , a b o u t 2 0 ,0 0 0 t o n n e s o r 1 1 % o f t h e h o u s e h o l d w a s t e a r e

s e p a r a t e d a t th e s o u r c e. O u t s i d e t h e c u r r e n t s c o p e o f R E M S , a n d n o t s h o w n in F ig . 4, is

t h e h o u s e h o l d w a s t e t h a t t h e c o n s u m e r c a r r i e s b a c k t o h i s r e t a i l e r . A c c o r d i n g t o R V F

( 19 9 0 ), 9 7 % o f th e r e t u r n a b l e b o t t l e s a r e re u s e d , a n d m o r e t h a n 8 5 % o f a ll a l u m i n i u m

c a n s a r e r e c y c l e d .

I n o r d e r t o t e st d i f fe r e n t l ev e ls o f a g g r e g a t i o n i n th e p i l o t s t u d y , t w o c o m m u n i t i e s t h a t

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

t h e s a m e t y p e o f t es t f o r i n d u s t r i al a n d c o m m e r c i a l o r c o n s t r u c t i o n a n d d e m o l i t i o n

w a s t e .

4.2 Data and assumptions

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

c o m p o s t a b l e c o m p o n e n t s o f h o u s e h o l d w a s te a n d t he c o m b u s t ib l e c o m p o n e n t s o f

c o n s t r u c t i o n a n d d e m o l i t i o n w a s t e . T a b l e 2 s h o w s t h e a s s u m p t i o n s m a d e a b o u t t h e

s y s t e m e n v i r o n m e n t f o r t h e s c e n a r i o s .

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

B a se C a s e. T h e f ir st b o u n d a r y c o n d i t i o n t o b e c h a n g e d is th e w a s t e m i x : th r e e s c e n a r io s

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

s c e n a r i o e x a m i n e s t h e c o n s e q u e n c e s t h a t a n e m i s s i o n f ee o n n i t r o g e n o x i d e s h a s f o r th e

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

I n a ll s c e n a r i o s , e x c e p t f o r t h e B a s e C a s e , t h e m o d e l is g i v e n o p t i o n s f o r s e p a r a t i n g t h e

c o m p o s t a b l e p a r t o f t h e h o u s e h o l d w a s t e ( k i t c h e n r e s i d u e a n d w e t p a p e r ) . T h i s p a r t c a n

b e e i t h e r c o m p o s t e d o r a n a e r o b i c a l l y - d i g e s t e d i n l a r g e s c a l e p l a n t s . T h e r e a r e a l s o

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

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

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

s e p a r a t i o n d e g r e e s g iv e n i n T a b l e 2 a r e o n l y u p p e r l im i ts . T h e d e g r e e s a c t u a l l y u s e d a r e

d e c i d e d b y t h e m o d e l .

T h e i n c i n e r a t o r h a s t w o c a p a c i t y c o n s t r a i n t s f o r i n p u t w a s t e ; f i r s t , t h e r e i s a t e c h n i c a l

u p p e r l i m i t o f 7 5 0 ,0 0 0 M W h / y ( m e a n l o w e r h e a t i n g v a l u e ) a n d , s e c o n d , t h e r e is a

c o n c e s s i o n t h a t p e r m i t s i n c i n e r a t i o n o f u p t o 3 0 0 ,0 0 0 t o n n e s / y .

D a t a f o r th e w a s t e f l o w s a r e s h o w n in F i g . 4 . T h e c o n t e n t o f th e w a s t e f l ow s a r e in t h e

m o d e l d e s c r ib e d b y w a s t e c o m p o n e n t s . T a b l e 3 s h o w s t h e c o m p o n e n t s u s ed f o r t h e s tu d y

o f G 6 t e b o r g .



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TABLE

2

Summary of the scenario

s for the pilot study

System environment

Optional waste

Options for

Scenarios

Source separation

technologies

emissions control

Am

ount of waste

Base Case

Paper= 67%, glass = 32%*

None

None

198

9

Increased source separation

Paper < 75%, glass <50%

Compost

None

198

9

Biogas

$25

$50

$75

Compostable comp.t < 25%

Combustible comp.~t <25%

Compostable comp.'t 50%

Combustible comp.~ < 50%

Compostable comp.t < 75%

Combustible comp.:[: < 75%

Emission fees

Same as scenario $50

Compost

Incinerator:

198

9

Biogas

Ammonia inj.§

Catalytic red,II

Transports:

Engine¶E

New vehicles

increased amount of waste

Same as scenario $50

Compost

None

Percent increase

Biogas

rela

tive to 1989

WI0

+ 1

0%

W20

+ 20%

* Paper (PA) and glass (GL) from households.

"i" CompostabLe comp

onents of household Waste; kitchen residue (K R) and wet paper (WP). (KR; WP) < 25%~ 50%, 75%,

:l: Combustible comp

onents of construction/demolition waste; paper a

nd cardboard (PC), wood (WO) and plastic (PL). (PC; WO; PL)

< 25%, 50%, 75%.

§ Ammonia injection

in the combustion chambers of the incinerator.

II Catalytic reduction of the flue gases of the incifierator.

¶ Engine improveme

nts (including catalytic cleaning for diesel engines).



Municipal solid waste management

T A B L E 3

C o m p o s i t i o n o f i n p u t w a s te

85

Ho useho ld was te Indus t r i a l and com merc ia l was te

Cons t ruc t ion and demol i t i on was te

C o m p o n e n t s % * C o m p o n e n t s % *

Paper (newspapers ) PA 16 Pap e r and ca rd boa rd PC 18C a r d b o a r d C A 6 W o o d W O 33W e t p a p e r W P 19 M e t al s M T 7K itchen residue K R 26 Plastics PL 3Plastics PL 8 Text i les TX 7Lea the r , rubbe r , t ex til es LT 3 M iscel laneous non-com bus t ib l e s M N 31G l a s s G L 8

M e t al s M T 4M iscel laneous M I 10

* Values in we ight percent.

T A B L E 4

C o s t s a n d r e v e n u e s

C o s t s R e v e n u e s

T r a n s p o r t sTransfe r s t a t ionsPre -process ing p l an tlnc ince ra t ion p l an tDisposal faci l i t iesAnnua l i zed inves tment fo r new t echno logyPurchased electrici ty

Heat (dis t r ic t hea t ing)Electrici tyRecycled materials:

p a p e rso i l f rom compos t

glassBiogas

T a b l e 4 s h o w s t h e c o s t s a n d r e v e n u e s i n c l u d e d i n t h e s t u d y . F i x e d c o s t s f o r e x i s t i n g

t e c h n o lo g i e s a r e lo o k e d u p o n a s s u n k c o s t s a n d , c o n s e q u e n t ly , e x c l u d e d f r o m t h e st u d y .

F o r t h e i n v e s t m e n t s i n n e w t e c h n o l o g y , a re a l r a t e d i s c o u n t o f 6 % is u s e d . T h e c o s t s t o

w a s t e p r o d u c e r s f o r t h e s o u r c e s e p a r a t i o n a r e e x c l u d e d . T h e t e c h n i c a l a n d e c o n o m i c

d a t a u s e d i n t h e p i l o t s t u d y a r e d o c u m e n t e d i n G i p p e r t h ( 1 9 9 0 ) .

4.3 Results

F o r t h e s c e n a r i o s s t u d ie d , t h e r e s u l ts s h o w t h a t c o m p o s t i n g is a c o s t- e f f ec t i v e a l t e r n a t i v e

t h a t c o o p e r a t e s r a t h e r t h a n c o m p e t e s w i t h t h e e x i s t i n g i n c i n e r a t i o n . T h e m a i n i n c e n t i v e

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

f r o m t h e s o u r c e s e p a r a t i o n o f c o m p o s t a b l e c o m p o n e n t s . T h i s r el e as e d c a p a c i ty c a n in

t u rn b e u se d f o r t h e c o m b u s t i b l e c o m p o n e n t s o f th e c o n s t r u c t io n w a s t e, w h i c h w o u l d

o t h e r w i s e h a v e b e e n l a n d fi ll ed . N e a r l y t h e w h o l e p o t e n t i a l o f a v a i l a b l e s o u r c e s e p a r a t i o n

is u s ed , e x c e p t fo r a m i n o r p a r t o f t h e c o m p o s t a b l e c o m p o n e n t s . T h e i n c o m p l e t e ly u s e d

s e p a r a t i o n o f c o m p o s t a b l e c o m p o n e n t s i nd i ca te s t h a t c o m p o s t i n g is n o t a c o m p e t i t iv e

a l t e r n a t i v e w h e n t h e r e is f r ee c a p a c i t y i n t h e i n c i n e r a t o r . T a b l e 5 g i v es a s u m m a r y o f t h e

r e s u l t s f r o m t h e s c e n a r i o s .



TABLE

5

Summary of results

Systems cost*

Scenarios

(Relative base case)

New

technologies

Source separationt

Emissions control

Base Case

1.0

None

(Fixed, see input)

Increased source separa

tion

Paper (PA) = max

Glass (GL) = max

Combust.$ = max

$25

0.88

Compost

Compost.§ = 23%

$50

0.83

Compost

Compost.§ = 43%

$75

0.78

Compost

Compost.§ = 62%

Emission fees, NO,

Paper (PA)= max

(SEK/kg, NO,)

Glass (GL)= max

0 < NO,-fees < 11

0.83 < Obj. f. < 0.95

Compost

Combust.~ = max

0%

11 < NOv-fees < 67

0.95 < Obj.f. < 1.30

Compost

Compost.§ = 43%

4

3%1[

67 < NO,-fees

1.30 < Obj.f.

Compost

77%¶T

NO, reduction:

Increased amount of waste

Paper (PA) = max

Glass (GL) = max

Compost.§ = max

W

I0

1.02

Compost

Combust.$ = 12%

W20

1.23

Compost

Combust.$ = 2%

* Resulting value for the objective function (O

bj.L) relative Base Case (52.0 MSEK/annum) SEK, Swedish Krona.

t Values in weight perce

nt. The maximal separations (max) are described

in Table 1.

Combustible compone

nts of construction/demolition waste; paper and c

ardboard (PC), wood (WO) and plastic (PL).

§ Compostable compone

nts of household waste; kitchen residue (KR) and

wet paper (WP).

II Ammonia injection in

the combustion chambers of the CHP-incinerator.

¶[ Catalytic reduction of

the flue gases of the CHP-incinerator.




TABLE 6

Marginal values (shadow prices a) for source separated com pone nts in the $50 scenario

Waste components

Marginal values

Market pricer(SEK/tonne) (SEK/GJ*) (SEK/tonne)

Separated household waste:Paper (recycled)Glass (recycled)Wet paper (composted)Kitchen residue (composted)

Separated construction waste:Paper (incinerated)Wood (incinerated)

Plastics (incinerated)

315 24.3339 0-~ t

66 9.2

71 5.571 5.5

274 8.9

350125

* Lower heating values."i" Assumptions used for this study.

The component is not limited by its upper bound.The shadow price gives the "marginal value" of a limited resource [i.e. variable(s)]. That is, it shows how

much the objective function (i.e. the system cost) is changed if the system has access to one more unit of thelimited resource. Iv, = dP/db,; where y, = shadow price (or reduced cost) for constraint i, P = objective function,and b,= constraint i.] For example, a shadow price of - 10 SEK/tonne for separated glass shows that if it ispossible to separate one additional tonne of glass, the system would gain 10 SEK. The marginal valuespresented in the table are the negative of the shadow prices.

4.3.1 I n c r e a s e d s o u r c e s e p a r a t i o n

The options for source separation and recycling are of special importance for this

system, due to the limited incineration capacity. In Table 6 the benefits of source

separation are shown by the marginal values for separated com ponents for scenario $50.

The result shows that greater usage of combustible co mpo nen ts from construc tion waste

is beneficial, and that released incineration capacity for these components should be

obtained by an increased recycling of paper and glass instead of choosing a larger

composting plant. Noteworthy is the high value for recycling paper and glass and the

large gap (214 SEK/tonne) between market price and shadow price for glass recycling.The marginal value for extra incineration capacity is 60 SEK/MWh.

Relative to the Base Case, the energy conten t o f the waste sent to the landfill is reduced

in the three scenarios by 46%, 62% and 78%. This "energy recovery" results from the

redirecting of combustible components of construction and demolition waste to the

incinerator and from redirecting a smaller amo unt of household waste to the incinerator.

The changes for landfilled waste are shown in Fig. 5. The resulting heating values of the

waste mix sent to both the landfill and the incinerator are shown in Fig. 6.

4 . 3 .2 E m i s s i o n s f e e f o r n i t r o g e n o x i d e s

The model results show that taking technical measures at the incinerator is the only

action that is cost-effective if a NO,-fee is imposed on the system. Neither of the other

measures, engine retrofits for the waste vehicles or decreased incineration, are competit-

ive for the interval studied. Thus, the results previously presented for the separation of

compostable and combustible components are unchanged.

Figure 7 shows for what NOx-fees it is cost-effective to reduce the emissions, and by

what measures. Thus, the steps in the figure are the result o f several model runs for which

the NOx-fee has been gradually increased. No measures should be taken for fees up to




12 0

90

60

3 0

6 1

8 00

600

E-

400

2 00

0 0Ba s e Ca s e S c e n a r io $ 5 0 Ba s e Ca s e S c e n a r io $ 5 0

F i g . 5. W a s t e s e n t t o l a n d fi ll in t h e B a s e C a s e a n d f o r s c e n a r i o $ 5 0 . ( A s h e s a n d s l a g f ro m t h e i n c i n e r a t o r a n d

s e w a g e s l u d g e a r e e x c l u d e d . ) ( V I ) , H o u s e h o l d w a s t e ; ( m ) , i n d u s t r i a l w a s t e ; ( 1 1 ) , c o n s t r u c t i o n a n d d e m o l i t i o n

w a s t e .

1 2

1 0

7

N 8

2

> 6

~ 4

~ 2

II .

i ii ~ I I

I n c i n e r a t o r

0 I I I I

B a s e C a s e $ 2 5 $ 5 0 $ 7 5

F i g . 6 . M e a n l o w e r h e a t i n g v a l u e s f o r w a s t e s e n t t o i n c i n e r a t i o n a n d l a n d f i l l i n g . ( A s h e s a n d s l a g f r o m t h e

i n c i n e r a t o r a n d s e w a g e s l u d g e a r e e x c l u d e d i n t h e v a l u e s f o r l a n d f il l ed w a s t e . )

11 S E K / k g . F o r f e e s b e t w e e n 11 a n d 6 7 S E K / k g , i t is c o s t - e f f e c t iv e t o u s e a m m o n i a

i n j ec t io n in t h e c o m b u s t i o n c h a m b e r . F o r f e es a b o v e 6 7 S E K / k g , t h e c a t a l y t ic r e d u c t i o no f t h e fl ue g a s es s h o u l d b e u s ed i n s t e a d . ( F o r t h e p i l o t s t u d y a r e s tr i c te d t e c h n o l o g y d a t a

b a s e w a s u s ed . A d e t a i l e d s t u d y w o u l d i n c l u d e m o r e a l t e rn a t i v e s f o r N O , . -r e d u c t i o n .)

4 .3 .3 hwrease d amount of waste

T h e m o d e l r e s u lt sh o w s t h a t a g e n e ra l i n c re a s e in t h e a m o u n t o f w a s te p r o d u c e d in t h e

r e g io n i n c re a s es th e v a l u e o f c o m p o s t i n g a n d d e c r e a s e s t h e v a lu e o f b u r n i n g c o n s t r u c t i o n

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

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




60 0

E4 00

0z

¢ - ,

200

P r e s e n t s y s te m

Ammonia injectionT

I

I

I

I

I

. I

Combustioni

I

I

I

I

~ T r a n s p o r t sI

20

C a t a l y t i c r e d u c t i o n

40 60 80 100

Emission fee ISEK/kg, NOx )

F ig . 7 . A m o u n t o f N O , r e s u l ti n g fr o m t h e w a s t e m a n a g e m e n t s y s t e m , f o r d if f e r en t N O , f ee s. ( T h e d o t t e d l i n e a t4 0 S E K / k g s h o w s t h e N O , - fe e i n t r o d u c e d i n S w e d e n i n 1 99 1) .

5 0 0

.~ 4.ooe ,

e .

3O003

200

o

In c rease

Scen a r io

_ - - - -o ( ~ )

- ~ ~A(KR)l ~ (wP}

" " -~ (PL)c,wo)

0% 10% 20%

$ 5 0 WlO W2 0

F i g . 8 . M a r g i n a l v a l u e s o f s o u r c e s e p a r a t e d c o m p o n e n t s i n t h e s c e n a r i o s , W I 0 a n d W 2 0 , w i t h i n c r e a s e d

a m o u n t o f i n p ut w a s te t o W A M S . ( - - Q - - ) , P a p e r ( PT ); ( - - 0 - - ) , g la ss ( G L ) . C o m p o s t ib l e c o m o n e n t s =- - A - - , k i tc h e n r es id u e ( K R ) ; - - O - - , w e t p a p e r ( W P ). C o m b u s t i bl e c o m p o n e n t s = - - [ ] - - , p la s ti c ( P L) ;

- - I 1 - - , p a p e r a n d c a rd b o a r d ( P C ) a n d w o o d ( W O ) .

Figure 8 illustrates this result by showing how much the marginal values for the source

separation constraints change as the amount of waste increases. The components with a

marginal value of zero are separated, however not up to the maximum levels.

The benefits of separating and recycling paper and glass are, as shown previously,

greater than for the other components. However, the value of glass is not changed, when

the input waste is increased. The explanation for this is found in Fig. 9, which shows that



90

300

J. Sundberg et al .

Upp er l imi t fo r i npu t qu an t i t y 3000~ - Upper l imit for input energy

"~ 200

100

200G

1000

0 0

Increase 0% 10% 20% 0% 10% 20°b

Scenario Base Case $50 Wl0 W20 Base Case $50 Wl0 W20

Fig. 9. Composition of waste at the incinerator for the scenarios, Wl0 and W20, with increased amount of

input waste to WAMS. ([ ]) , Household waste: (• ) , industrial waste; (m ), construction and demolition

waste).

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

C o n s e q u e n t l y , n e i t h e r o f t h e l i m i t s w i l l c h a n g e t h e v a l u e f o r g l a s s r e c y c l i n g .

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

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

v o l u m e r e d u c t i o n . [ N o t e t h e g a p b e t w e e n t h e b a r s a n d t h e u p p e r l im i t f o r i n p u t w a s t e in

t h e l e ft c h a r t o f F ig . 9 , a n d a l s o t h e d i f f e re n c e i n m a r g i n a l v a l u e s f o r s e p a r a t i o n o f p l a s ti c

( P L ) a n d w o o d , a n d p a p e r a n d c a r d b o a r d ( P C , W O ) i n F i g . 8 . ] T h i s s i t u a t i o n c o u l d

c h a n g e h o w e v e r , i f t h e r a t i o b e t w e e n l a n d f il l in g c o s t s a n d e n e r g y p r i c e s ri se s. T h e u p p e r

l imi t f o r i npu t e ne r gy i s r e a c he d in a l l s c e na r io s .

5. Summary and conclusions

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

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

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

p r o d u c t s . I n o r d e r t o d o s o , t h e s e c o m p a n i e s h a v e t o i n t r o d u c e n e w a n d " ' c l e a n "

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

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

T h e p l a n n i n g s i t u a t i o n i s c o m p l e x s i n c e t h e r e a r e m a n y f e a s i b l e o p t i o n s t o b e

c o n s i d e r e d f o r t h e f u t u r e w a s te m a n a g e m e n t s y s te m . I t is c o m p l e x a l so b e c a u s e t h e r e a r e

m a n y u n c e r t a i n t ie s a s to h o w t h e e n v i r o n m e n t o f t h e s y st e m w ill d e v e l o p . H o w w ill t h e

m a r k e t f o r m a t e r i a l p r o d u c t s d e v e l o p ? W h a t e n v i r o n m e n t a l r e s t r i c ti o n s w ill b e i m p o s e d

in t h e f u t u r e ? W h a t d e g r e e o f s o u r c e s e p a r a t i o n c a n b e a ch i e v e d ?

T h e M I M E S / W A S T E m o d e l p r e s e n t e d i n t h i s p a p e r i s d e s i g n e d t o b e a c o m p r e h e n -

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

m e n t s y s t e m s . It h a s b e e n d e v e l o p e d i n o r d e r to m e e t th e c h a n g e s in w a s t e m a n a g e m e n t

d e s c r i b e d a b o v e , a n d t o b e u s e d b y s y s t e m m a n a g e r s a n d o t h e r a c t o r s i n t h e s y s t e m t o

p r o d u c e c o m p r e h e n s i v e p la n s.

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

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

a system approach to municiple solid waste management - a pilot study of goteborg

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