LIFE-CYCLE CHAIN ANALYSIS INCLUDING RECYCLING
Author: A.J.D. Lambert
Technische Universiteit Eindhoven
P.O. Box 513, 5600 MB Eindhoven
Attn. A.J.D. Lambert
TM/AW Pav. H03
Phone: +31-40-2474634
Fax: +31-40-2444602
E-mail: a.j.d.lambert@tm.tue.nl
dr.ir. A.J.D. (Fred) Lambert studied theoretical physics and is actually working as an
assistant professor at Technische Universiteit Eindhoven. He carries out research on
environmental and energetic aspects of production processes, with an emphasis on
quantitative modelling.
This paper appeared in the book:
J. Sarkis (ed.), 2001, Greener Manufacturing and Operations. Sheffield: Greenleaf
Publishing. Chapter 2, 36-55.
1
Chain analysis
ABSTRACT
As reuse and recycling of discarded products crosses the boundaries of individual
enterprises, a chain approach is required, including consumption and waste
processing. Product design can not be considered isolated from the full product lifecycle. Life-cycle modelling is treated, focused on discarded complex consumption
goods. Some characteristics of this particular waste stream are presented. Suggestions
have been made for modelling the resulting life-cycle chains, including existing
methods such as life-cycle assessment. As the bottleneck of future life-cycles appears
to be in the amount of shredder residue, this topic is emphasised and
recommendations to reduce this problem are formulated.
2
LIFE-CYCLE CHAIN ANALYSIS INCLUDING RECYCLING
A.J.D. Lambert
1. Introduction
In this chapter, a general discussion is presented on the different aspects of life-cycle
chain analysis. As the closing of cycles is advocated as a principal condition for
sustainable development, the concept of life-cycle chain needs to be expounded.
There may be some confusion regarding the different viewpoints on the life-cycle that
are used in the literature, so it is worth mentioning that two different concepts are
applied here: the conceptual life-cycle and the material life-cycle.
The conceptual product life-cycle refers to the product as a concept, namely from an
idea, via research and development, to production, introduction into the market,
market penetration, becoming outdated and, finally, gradual substitution by a different
product. This approach is of principal interest in the domains of marketing and longterm planning.
The material product life-cycle, by contrast, refers to the product as a physical object.
The life-cycle is the complete sequence of processes in a product’s life, including
production, consumption, and waste processing. This is often called a cradle-to-grave
approach, because the cycle extends from materials extraction up to discharge of
materials. This is used in the materials and energy analysis of products and
particularly in environmental analysis. Here, the cumulative environmental impact of
a product on the environment is quantified. At present, the most frequently used
method in this field is Life-Cycle Assessment (LCA). This is briefly discussed in
section 4 of this chapter.
Chain analysis is a valuable tool in environmental management, particularly for
effectuating product stewardship and product responsibility [Hart 1997, Veroutis
1997]. These concepts, originating from the process industry, are now incorporated in
the legislation of about 40 industrialised countries and implemented in many
industries. This typically goes beyond the system boundaries of a single company and
at a minimum it compasses the domain of its suppliers and customers but, more
frequently, even a substantial part of the chain. As a result, individual enterprises
require insight into the entire product’s life-cycle chain. This reveals the integral
consequences of product and process modifications on the environmental impact, but
also on other topics such as energy use and costs. Since enterprises are increasingly
concentrating on their core businesses and now outsource much of their activities, an
approach that strictly focuses on the enterprise and excludes other aspects is not
viable.
2. Product-process chains
2.1. Aggregate chain modelling
As the emphasis is on material product life-cycles in this chapter, a basically physical
approach is required, in which energy and material flows play a central role. In
environmental analysis, many features are closely connected to physical flows, such
as raw materials consumption, production, energy consumption, waste, and emissions.
Physical flows are subjected to laws of nature, such as mass and energy conservation,
and chemical reaction equations. These relations can be used for balancing. The
physical approach is based on industrial ecology [Graedel 1994, Ayres 1996 and
Erkman 1997] in which the exchange of material flows in the economy is treated
similarly to that in ecosystems.
3
In the process industry, material flow analysis is routinely performed. Though a
similar method is useful in discrete manufacturing, in common practice the
description of flows is not based on physical properties here but rather on numbers of
items and their composition in different discrete parts. This is reflected in the usual
Enterprise Resource Planning (ERP) systems for discrete manufacturing, which are
based on bills-of-materials (BOMs), i.e. lists of parts. For support of environmentally
oriented decisions, the BOMs have to be complemented with information on mass and
composition.
Though effects due to discretization, storage etc. complicate a physical description of
discrete manufacturing, these are smoothed over the rather long periods of time that
are characteristic of chain analysis. This results in a method of description similar to
that of the process industry. There too, discretization is present, due to batch-wise
production and environmentally relevant periodic processes, such as cleaning and
maintenance activities.
Unification of the method of description is indispensable in life-cycle chain analysis,
because a chain includes a combination of process and discrete manufacturing.
Modelling is the creation of a simplified map of reality, with conservation of the
features that are essential to the objective of the modeller. This means that a part of
reality can be modelled in many different ways. Models of product life-cycle chains
are set up via concepts from systems theory. A system is defined here as a number of
objects and the relations between objects and with the environment of the system. A
system boundary is defined between a system and its environment. Initially, the
system is treated as a black box. From this only its responses to signals from the
environment are measurable, without further knowledge of the system’s inner
structure. Opening of the black box reveals the objects of which a system is
composed. Each of these objects is a black box as well, which in turn can be opened.
Such a process is called a disaggregation process. If this is repeatedly applied to a
system, a hierarchy of levels of aggregation is established.
Although the elements of a system seem well defined in theory, they often are fuzzy
in practice. The system boundary of an enterprise, for example, is not simply its fence.
As a matter of fact, the boundary of a much more abstract object, such as a product
chain, is even more ambiguous.
As the objective of industrial ecology is to model material and energy flows in
economically relevant processes, the relations between (sub-) systems and their
environment are principally defined through exchange of material and energy flows.
In industrial ecology, a distinction is made between the technosystem and the
ecosystem. The technosystem is the physical basis of the human-controlled economy.
It involves raw materials, buildings, machines, intermediate products, consumer
goods, wastes, etc.
The ecosystem or natural system acts as the environment of the technosystem.
Material resources in the ecosystem are organised in closed loops. This means that
residual materials such as excrements and dead organisms, are reused up to a
considerable extent and thus virtually no waste is produced. A multitude of cycles are
present, involving both the biotic and the abiotic part of the ecosystem: the water
cycle, the carbon cycle, the nitrogen cycle, the sulphur cycle, etc.
In contrast, material flows in the technosystem show essentially linear characteristics.
Copper, for example, is mined as an ore and subsequently processed. Next, it is used
in products. After a shorter or longer period of time, these are discarded. After that,
much of the copper is not reclaimed, but rather discharged to the ecosystem,
4
principally because of the product’s structure, in which the copper is combined with a
lot of different materials. Theoretically, many materials are not even recoverable, see
section 2.5. Besides this, the technosystem differs from the ecosystem by its
dependence on exhaustible fossil energy resources, instead of solar energy. Both
properties result in basically linear characteristics. This is illustrated in figure 1 by
means of a so-called product-process chain [van der Voet 1995ab, Sheng 1998]. It
represents a product life-cycle by an alternate sequence of transformation processes
(rectangles) and products (arrows). In section 2.4, some basic features of such a
representation are explained. Figure 1 illustrates that, after consumption, some
processes take place to prepare the discarded products for discharge. For the sake of
simplicity, ancillary flows, energy use, and process emissions are omitted in this
picture.
[Figure 1. Aggregated linear product-process chain.]
2.2. Decomposition
When complex products are considered, it is useful to decompose the linear productprocess chain of figure 1. The production phase is subdivided into three subsequent
phases:
 Materials production. This establishes the intrinsic properties, such as
composition. It is the domain of the process industry.
 Parts production. This establishes the extrinsic properties, such as shape and size.
It is the domain of discrete manufacturing.
 Assembly. This establishes the functionality of the product. It is the domain of the
assembly industry.
Figure 2 shows the disaggregated product-process chain.
[Figure 2. Product-process chain for complex products, including reuse and
recycling.]
In this scheme, the upgrading process is disaggregated similarly to the production
process. Three degrees of reuse are discernible here: product reuse, parts reuse, and
materials recycling [Krikke 1998]. This requires a sequence of processes for
reclamation of the desired objects. Crucial to this sequence is the disassembly process.
Disassembly is a non-destructive and reversible process for removing complete and
intact parts and/or subassemblies. The term dismantling or dismounting is used for
destructive separation of parts from an assembly, aimed at materials recycling or
freeing of other parts. Disassembly and dismantling are not sharply distinguished. In
practice, a combination of both processes is carried out, only up to a definite
disassembly depth. This is called partial or selective disassembly. It provides us both
with parts or subassemblies that can be reused, and with parts or subassemblies that
are principally removed to facilitate the subsequent disassembly operations, see
section 3.4.
A freeing process, frequently involving shredding, grinding or a similar destructive
process follows disassembly/dismounting. This results in fragments of material that
have a more or less homogeneous composition and that are separable into different
fractions via separation. Magnetic separation for recovery of ferrous materials, and
eddy current separation for the recovery of non-ferrous materials are the most
frequently used. The remaining shredder light fraction (also called shredder fluff or
shredder residue) includes glass, rubber, plastics, textile, cardboard, etc. Subsequent
5
mechanical or chemical separation steps, such as float and sink separation, gravity
separation, for recovery of many of these materials are available on a laboratory scale.
These are, however, often infeasible from an economic point of view because of the
variety, the inhomogeneity (often composite materials are used), and the low specific
value of the materials that are still present. Moreover, many of these materials are
contaminated by additives.
Landfill of shredder light fraction is heavily restricted and its incineration is subjected
to legislation that prescribes strictly controlled conditions, because it can contain
harmful substances. This makes the final treatment of shredder residue expensive,
which is an incentive to reduce its bulk. This condition heavily influences the
arrangement of the previous production steps, particularly the disassembly process.
Therefore, product design has to account for easy disassembly of the parts, for a
restricted variety of materials, and for avoidance of materials, which can not be
recycled, such as composites. In practice, this means that the product design must
proceed simultaneously with the design of the upgrading system. Such an approach is
included in design for disassembly. Many products that are presently discarded do not
fulfil the above-mentioned condition. This severely restricts disassembly.
2.3. Waste production
In a product life-cycle, a distinction is made between process wastes and product
wastes.
Process wastes originate from the various processes in the product life-cycle,
including consumption and the phases of the upgrading and recovery processes. In
many cases, these can, with minor effort, be recycled to the original production
process from which they originated. This is called internal or micro recycling. Waste
from plastics moulding, for instance, is fed back to the moulding process because its
composition is known and fits the process requirements. Because internal recycling
proceeds within the black boxes, it is not indicated in figure 2. Only external
recycling is visualised there, e.g., by the arrow that points from parts production back
to materials production.
Product wastes consist of discarded products, which no longer provide the services
they were intended for. Secondary materials from product wastes can often only be
upgraded to a lower degree of quality than the original materials, so they have a
restricted range of applications. This can imply that they are utilised in products that
are described by a different chain. When they are used in the same complex product,
it will be for a qualitatively lower application. This takes place, for instance, in
automobile manufacturing, in which secondary materials originating from parts with
strict mechanical specifications (bumpers) are recycled to parts that are not subjected
to these requirements. After several cycles in ever-lower degree applications, such
materials finally act as a filling material in products. Such a sequence is called
downcycling or cascading. This can substantially raise the time of residence of a
material in the technosystem.
2.4. Production processes
Essential characteristics of a production process include:
 Addition of value to a material object via a transformation process.
 Requirement of energy.
 Production of residual material flows, called waste and emissions, in addition to
products. The latter are discharged to the atmosphere or water.
6
In addition to energy carriers, various ancillary materials and utilities are required for
production. These are not meant to be part of the final product but leave the process as
waste or emissions.
The outgoing materials can be subdivided into various groups:
 Products. These are the desired result of the process. They represent the greater
part of the value added. Products can serve as an intermediate product, or as an
ancillary for a subsequent production process. In other cases, these are intended
for consumption or as a capital good.
 Co-products. These represent a substantial value, although they are not an
intended result of the process.
 By-products. These are also unintentionally produced, but they represent a modest
positive value. Frequently, their specific value (€/kg) is less than that of the
original raw material.
 Residual products. These are the process wastes that represent a negative value.
This means that one has to pay for the disposal of these materials. In many cases,
processing of these products can increase their value. Emissions to the
atmosphere, to the soil, and to the water, are also included in this category.
[Figure 3. Scheme of mass and energy flows in a production process.]
In figure 3, a scheme of a production process is presented. It shows the different
incoming and outgoing physical flows. Due to mass and energy conservation, the
amount of mass and energy that enters the system equals the amount that leaves it.
Inevitable irreversibilities in the process always result in a loss of quality of the
energy. Residual heat, for example, is characterised by a low exergy content and a
low energy density. This impedes many applications.
Quality of material flows is hardly quantifiable, but it is also connected to
applicability, which depends on many properties, such as purity in the case of
materials, and dimensions in the case of parts. In economics, the many aspects of
quality are combined to the market price of the respective material or part. This price,
however, also includes many aspects that are not related to quality.
Process and product design must account for the complete picture, and should
optimise the total added value of the outgoing products with respect to the incoming
ones.
One of the means for this, is minimising the amount of residual products. The
following hierarchy of measures to attain this, is frequently advocated:
 Reduction of the amount of waste.
 End-of-pipe measures for reducing harmful waste.
 Reuse of residual flows as materials.
 Incineration.
 Landfill.
Though complete closing of the chain is impossible from a theoretical point of view,
in many individual companies, all outgoing materials, except the emissions to the
atmosphere such as flue gases, remain inside the technosystem. Even the wastes are
not directly discharged, but transferred to waste processing companies, in which they
are further processed prior to final discharge.
From this, it follows that a typical product-process-chain of a product is not linear, but
rather a branched network, with nodes connected to each process and each product
flow. Product flows are governed via markets, in which supply and demand are
balanced via a price mechanism. Frequently, such a market is open, which means that
7
product flows can cross the system boundaries. The basic features of such a network
are depicted in figure 4.
[Figure 4. Convergence and divergence on the product and process level.]
Here, markets are related to product nodes. Product flows from different processes,
such as 1a and 1b, can be combined here. A product flow can also be distributed
between different processes, such as 2a and 2b. Moreover, products can be imported
and exported across the system boundaries.
Processes are connected to process nodes because they have multiple inputs
(convergence) and multiple outputs (divergence).
Such an approach has always been applied in the process industry, for lies at the heart
of its operation. A typical example of divergent operation is a petroleum refinery.
Here, a feed of changing composition is separated in many products. This process has
many degrees of freedom, which can be established depending on market
circumstances. A typical convergent operation is an assembly line: parts are combined
to form a single, complex product.
When one focuses on physical flows, as in environmental configurations, all these
flows have to be treated similarly, i.e. as if they were valuable products. This is
evident, because considerable costs or benefits are connected to the residual flows that
were formerly practically free. Therefore, this approach is both environmentally and
economically beneficial.
2.5. Consumption processes
From a physical point of view, consumption processes are similar to production
processes. However, the value of the transformed material object is not created but
rather destroyed during consumption, as it is applied for providing services to the
user. Actually, not the product but the service is normative, and substitution of
products by different ones that offer the same service at the cost of less materials is
possible. This is called dematerialization.
Consumption can cause a significant amount of process wastes, and considerable
energy use. Driving a car during its lifetime, e.g., requires an amount of energy of
about ten times the cumulative amount of energy that is needed for its production.
Besides this, product waste is generated when the car is discarded. Because there are
many different consumer goods and ways of consumption, the product wastes show
essential differences.
Consumption processes can be classified in different ways:
 Consumption of materials and of discrete products. One uses a litre of petrol, a
kilogram of meat, but an item of a car.
 Active and passive consumption. In active consumption, the consumer goods are
physically and/or chemically completely transformed. Consequently, these are not
recoverable. Examples are food and fuel. Residuals are emitted or remain as solid
waste, e.g. ashes. In passive consumption, although the goods gradually lose their
functionality, they retain their principal properties.
 Instantaneous and durable consumption. Many materials are instantaneously
consumed, but also a lot of discrete products have a very short time of residence in
the consumption process. Disposables, packaging materials, newspapers and
similar products are used once and almost instantaneously finish as household
waste. Durable consumer goods have a much longer time of residence, up to many
years, before they are discarded.
8

Diffuse and discrete consumption. If a good is consumed diffusely, it can not be
recovered, because the resulting product waste is dispersed. This holds for many
products, e.g. cleaning agents, and also for the wear of discrete products, e.g.
tyres. After discrete consumption, a product remains localisable and,
consequently, recovery is possible. This can take place directly, via a take-back
network, or indirectly, e.g., via separation of municipal waste.
Consumption of a car, for example, is passive, durable, and discrete. Consumption of
petrol is active, instantaneous, and diffuse.
Consumption of capital goods is comparable to that of consumer goods. A relevant
difference is that capital goods are used in production processes and, consequently,
operate under completely different economic constraints. In the following sections on
complex consumer goods, the corresponding capital goods are implicitly included.
From a recycling point of view, there are additional differences, for capital goods are
in general more robust, such as trucks vs. cars, and discarded ones are often offered in
large and quite homogeneous lots, e.g. TL tubes or business computers.
3. Discarded complex consumer goods
3.1. The position of waste from complex products
Although a considerable share of discarded complex products consists of durable
household goods, comparable capital goods are also included. To evaluate the current
developments on processing of this stream, it should be positioned, both
quantitatively and qualitatively, within the framework of the general waste problem.
The definition of waste is rather fuzzy. An extended definition includes the “waste”
which is created via a mere displacement of materials. Examples are water, air, sand,
soils, part of the organic waste, and rock. Although the resulting material streams are
considerable, their environmental impact is modest. Usually, no statistics of such
streams exist.
Material streams that are recycled inside companies (micro recycling) are also not
well documented. Their environmental impact proceeds indirectly, e.g., by an
increased specific energy use of production processes.
The major part the registered waste streams, consists of bulk products, such as slag,
sludge, ashes, manure, and contaminated soil, which amounts to several tonnes/yr per
capita. These streams usually bear a large share of inert substances, such as water.
Building and demolition waste counts for about 0.5 tonnes/yr per capita. Much of this
can be recycled.
The amount of household waste shows a comparable figure. The share of paper (50
%) and glass (10 %) is recyclable. The organic share (20 %) can be composted. The
remaining share (20 %) can be roughly divided into 7.5 % ferrous and 1.5 % nonferrous materials, 4 % wood, 1.5 % textiles, 5.5 % rubber, plastics and comparable
materials. This share originate mainly from packaging materials, and also includes
discarded complex products.
Because of differences in definition, waste collection systems, and consumption
patterns, a complete and detailed set of data on discarded complex goods is not
available1. Moreover it changes rapidly over time, because of technological progress.
Cars, electric devices (white goods) and electronic devices (brown goods) are
1
Data on complex consumer goods mainly originate from German and Dutch sources, such as those
from the Dutch waste processing association, 1998/1999.
9
important constituents. An estimated amount is 50 kg/year per capita of discarded
cars, and another 50 kg/year per capita of coarse goods that also include furniture,
carpets, etc. The combined quantity of white goods and brown goods presently
amounts to approximately 25 kg/yr per capita, including 9 kg/yr per capita of capital
goods.
About 10 kg/yr per capita are white goods, e.g. refrigerators (1.2 kg/yr per capita),
washing machines, boilers, heating systems, cookers, etc.
About 4 kg/yr per capita are brown goods, e.g. TV sets and monitors (2 kg/yr per
capita) and computer systems (1 kg/yr per capita).
The total amount of printed circuit boards (PCBs) from all household and professional
devices, cars included, is about 0.5 kg/yr per capita.
Although the contribution of discarded complex consumer goods to the total amount
of waste is thus rather modest, it needs special attention. Its volume, its complexity,
its growth potential and the presence of many hazardous substances make conscious
processing both indispensable and difficult.
3.2. Cars and white goods
In cars, many hazardous parts and working fluids are present. The recoverable ferrous
and the non-ferrous fraction amounts to about 70 % and 4.5 % respectively, the latter
mainly consisting of aluminium, copper, zinc, and lead. There is a tendency for a
decrease of steel contents, in favour of light metals, plastics and ancillary equipment.
This is counteracting adequate recycling.
Presently, cars are drained, selectively dismounted, and subsequently shredded for
volume reduction and recovery of ferrous and non-ferrous materials. Consequently, a
considerable amount of shredder residue is left, consisting of dust, light materials such
as plastics, rubber, textile, and glass. Because cars consist of some rather large and
homogeneous parts, selective dismounting results in both recyclable parts and
reduction of shredder residue.
White goods also have a substantial metals content and several major and rather
homogeneous, dismountable parts. Typical composition figures (in weight-%) are as
follows.
For a washing machine of 80 kg: ferrous (50 %), concrete (20 %), electronics and
electric components (10 %), packaging and documentation (7 %). The remaining 13
% consists of non-ferrous materials and light materials such as plastics, glass, and
rubber.
For a refrigerator (35 kg), ferrous (63 %), copper (3 %), aluminium (5 %), working
fluids (3 %), plastics, rubbers, glass etc. (26 %).
3.3. Brown goods
The amount of 4 kg/year per capita for discarded brown goods does not seem
impressive. The real amount, however, is higher, because of the increasing share of
embedded electronics in non-electronic devices, particularly in cars. Actually, we are
only at the beginning of developments, in which electronics will penetrate into
virtually all domains of consumer goods, e.g. smart buildings, and control systems for
cars and even small household devices.
Brown goods are characterised by neither a high metals content nor by the presence of
many major and homogeneous parts. On the contrary, these are complex and usually a
multitude of hazardous substances can be identified. Hazardous working fluids, such
as oil, fuel, refrigerants, electrolytes are often present. Many hazardous substances
such as pigments, soldering connections, alloys, and additives to plastics, glasses, and
10
rubbers, are dispersed in materials. Hazardous parts are present, such as batteries that
contain heavy metals and electrolytes, displays containing fluorescents, and switches
that contain mercury. Cathode ray tubes can consist of up to 8% Pb and also contain
Ba and Cd for protection against X-rays. In electronic circuitry, a multitude of
elements is present in varying concentrations. Metals account for about 27 % of the
PCB’s weight. Typical concentrations in PCBs are Fe 10%, Al 5%, Cu 5%, Pb 1%, Ni
1%, Sn 2%, Zn 1%, Mn 1%, Br 1%, and traces of many other hazardous and/or
precious metals (Ag, Au, Pt, Pd). Component housing (plastics and ceramics) and the
support (glass fibre, phenol, and cardboard) account for the remaining 73 weight-% of
PCBs. Theoretically, all these materials can be reclaimed, but this requires a complex
sequence of processes, which is out of the question, as concentrations are too low and
too variable.
There are a number of trends in brown goods that include both opportunities and
threats with respect to recycling:
 Rapid technological change, resulting in massive introduction of new types of
products, e.g. GSM sets, and a rapid succession of generations of existing devices.
 Miniaturisation, resulting in smaller parts with complex composition, which
complicates their economically feasible dismounting.
 Introduction of dedicated materials. Easily recoverable materials such as iron, are
replaced by hardly recoverable materials with a complex composition, such as
composites.
 Irreversibility. To reduce the number of parts, those aimed at reversible
connections (screws etc.) are replaced by irreversible connections such as via
clicking, soldering, welding etc. This severely complicates disassembly and
subsequent materials separation.
 Dispersed functionality. Miniaturised displays, sensors, processors, electric
motors etc., are increasingly applied in various devices and even in buildings.
 Enhanced reliability. This extends the durability and, consequently, the time of
residence in the technosystem. For instance, the standard warrantee period for
household equipment is shifting from 1 year to 3 years.
 Modularity. This enables repair and upgrading via exchange of modules rather
than via replacement of the complete device. Modularity is also helpful in
adequate disassembly operations and in reuse of intact disassemblies.
 Commonality of parts and modules within different types and generations of
products.
3.4. Chain considerations
In industrialised countries there is a tendency towards separate recollection of
complex household goods. Consequently, these are withdrawn from landfill or
incineration, which enhances the quality of slag and filter residues from the waste
incinerators. Particularly, the content of Br (from flame retardant), As
(semiconductors), Cu, Cr, Hg, Pb (cathode-ray tubes), Cd and Ni (from batteries) in
slag will be strongly reduced. This enables utilisation of the bulk of the slag in road
construction etc. Processing of discarded complex products finally results in a certain
amount of shredder residue. Incineration and subsequent storage of the slag should
proceed analogous to that of hazardous waste, which is expensive. These
circumstances are in favour of reduction of the amount of shredder residue. This
requires appropriate methods for processing the collected products.
11
Actually, one of the first steps in processing involves selective or partial disassembly.
The disassembly depth is determined by a combination of technical, economic and
environmental requirements [Lambert 1999] such as:
 Removal of hazardous working fluids (e.g. degassing and draining of fuel).
 Removal of components that contain hazardous substances (e.g. batteries and
electrolytic capacitors).
 Collection of valuable parts (e.g. lenses).
 Collection of parts that contain precious materials (e.g. catalyzers).
 Removal of parts for freeing some relevant components (e.g. housing or
fasteners).
 Removal of parts that can contaminate other components or fractions.
 Removal of parts for technical reasons (e.g. cables).
 Removal intended to the reduction of shredder residue (e.g. interior lining of cars).
Selective disassembly is not a simple task for the present generation of brown goods.
In fact, only rough dismounting operations such as the removal of the housing, the
separation of principal modules, removal of PCBs, major coils, batteries, and cathoderay tubes are practicable. PCBs and comparable complex parts are shredded and,
subsequently, some metals can be separated from the resulting fragments.
Obviously, the actual method is far from ideal. Increased disassembly depth and better
separation of the materials is virtually impossible from both an economic and a
technical point of view. Changes in design can improve this situation.
With respect to the design for recycling, the following requirements can be listed:
 Dematerialisation.
 Application of reusable and easily detachable modules.
 Enhanced commonality of parts and modules in different product types and
product generations.
 Enhanced durability.
 Application of a restricted range of materials. This facilitates recycling and thus
reduces the amount of waste.
4. Life-cycle assessment
4.1. Standard LCA
Though an extensive treatment of the LCA method falls beyond the scope of this
contribution, a short introduction will be presented, focused on the relation between
LCA and recycling.
The definition of LCA is as follows [Guinée 1993ab]:
Life-Cycle Assessment (LCA) is a technique for assessing the environmental aspects
and potential impacts associated with a product, by:
 Compiling an inventory of relevant inputs and outputs of a product system.
 Evaluating the potential environmental impacts associated with those inputs and
outputs.
 Interpreting the results of the inventory analysis and impact assessment phases in
relation to the objectives of the study.
LCA studies the environmental aspects and potential impacts throughout the product's
life (i.e. cradle to grave) from raw materials acquisition through production, use and
disposal. The general categories of environmental impacts needing consideration
include resource use, human health, and ecological consequences.
12
This definition is from ISO 14040, an international standard within the ISO 14000
series. ISO 14000 encompasses the different aspects of environmental management
systems in enterprises. ISO 14040 imposes standards on the LCA tool, based on
experience that has been gathered during the past thirty years.
The aim of LCA studies can be:
 Product and process comparison and evaluation.
 Improvement analysis.
 Design aid.
In the list of references, some basic papers on LCA are mentioned. Many more
papers, handbooks, and textbooks are actually available. Some of these are
theoretical, other are practical or devoted to detailed studies on materials, products,
and processes. Results of these studies are compiled in databases, which are added to
LCA software tools, such as SimaPro.
The development of LCA started in the late sixties, when the first systematic studies
were carried out that encompassed various relevant environmental impacts of a
product during its complete life-cycle. These studies were focused on a comparison of
different packaging systems, such as bottles and cartons. The need for a universally
applicable method resulted in the ISO 14040 standard.
The basic structure of the chain, which is studied in LCA, is presented in figure 5. In
its most simplified form, it shows a convergent tree structure. The only possible
divergence is a fixed share of the discarded product in different final treatment
methods, such as landfill or incineration.
Although LCA is a powerful tool for studying linear and mainly convergent chains,
two objections become apparent in situations with recycle loops, such as depicted in
figure 2, and with divergent processes, such as depicted in figure 4.
This mainly results from the essentially different approach in LCA of products and
wastes. This implies that no use can be made of mass conservation laws. In LCA, the
environmental impact is connected to processes, which use resources that contribute
to exhaustion, and which produce emissions and wastes that have an environmental
impact.
Recycling and waste treatment processes, by contrast, use wastes and produce more
useful products that substitute virgin materials in various processes, besides residuals
such as slag and emissions. In practice, upgrading plants are often indeed only judged
by their outgoing waste flows. Therefore, the main concept of LCA is not principally
meant to include processes that use waste as a resource. For the treatment of branched
product networks with various loops and nodes, which include recycling processes,
extensions to standard LCA are required. A brief discussion of these extensions is
presented in the following section.
[Figure 5. Tree structure of a typical LCA.]
4.2. Extended LCA including recycling
As discussed in the previous section, the usual LCA approach complicates the
extension of this method to product chains with recycle loops and divergence
[Tillman 1994, Azapagic 1999]. A modelling method on the basis of material balance
equations, can match these problems. Such an approach is illustrated in figure 6. A
simple chain with recycling is depicted here. The considered system is indicated by
the shaded rectangle.
13
The system boundaries refer both to the parts of the technosystem that are not studied
here and to the ecosystem. Characteristic parameters for the system of figure 6 are the
recycling factors  , e.g.:
x
2  3
x2
These factors represent the share of discarded products that are recollected for
upgrading and recycling.
[Figure 6. Example of a chain diagram with recycling.]
Loss factors λ indicate the share of raw material that is not incorporated in the
resulting product. In this example, two loss factors are discerned:
x
x
1  5
3  9
x1
x3
In addition to the parameter definitions, balance equations are required, both for the
product nodes and for the process nodes:
x2  x6  x8
x4  x5  x7  x9
x1  x5  x6
x2  x3  x7
x3  x8  x9
If storage effects in the system can be neglected, the mass balance holds both for the
complete system and for each part of the system. This results in x1  x4 . This
expression simply states that the amount of waste that leaves the system equals the
amount of raw materials that is required by the system.
The environmental impact of the production of an amount of consumer goods x2
consists of the following contributions:
 Depletion of resources: 1 x1
 Discharge of waste:  4 x4
 Contributions of processes:  1 x1   2 x2   3 x3   4 x4
Here i, δi, and πi are constant factors that indicate the amount of environmental
impact per unit of flow.
Some of the parameters of a product-process chain are principally technically
determined, e.g. the amount of cokes that is required to produce one tonne of raw
iron. Other parameters, such as the recycling factor, can be influenced. In practice, the
relations between the different quantities are far more complicated than is indicated
here. As a matter of fact, the costs, the energy use, and the environmental impact of
the recycling process increase more than proportionally with respect to the recycling
factor. In most of the cases, complete recycling can not be realised because of
fundamental theoretical constraints. A typical example of the behaviour of the impact
of the recycling process in connection with the recycling factor, is depicted in figure
7.
[Figure 7. Specific environmental impact of recycling vs. recycling degree.]
14
This modelling method, on the basis of mass balances, can be used in combination
with standard LCA analyses.
To deal with outgoing flows of products, an additional extension of standard LCA is
required. Figure 8 shows such a system.
[Figure 8. Example of a chain diagram with recycling and exchange.]
Here, the recycle flow x8 is fed to a different product chain instead of being returned
to process P1. In this case, the node equations have to be adapted, and an additional,
negative contribution to the environmental impact due to x8 must be added, viz.:
 8 x8
This accounts for the amount of virgin materials that is substituted by the secondary
material, represented by flow x8.
It is essential that this system is divergent, as it generates two products, namely those
represented by x4 and x8. This requires adequate allocation of the environmental
impact of the processes to those products. This allocation problem can not be solved
unambiguously. One has to attribute weight factors that distribute the environmental
impact (and costs, energy use, etc.) of the different processes to the different products
in a reasonable way. Usual methods involve allocation according to the market value
of the respective product, and to the amount of raw material that is represented by the
product. It is beyond the framework of this chapter to go into detail on allocation
problems. In the list of references, some papers on this subject are included.
5. Conclusions.
In this chapter, the requirement of “closing of the chain”, that is advocated by the
authorities for stimulating sustainable production, is combined with the already
existing concepts of mass flow modelling of product chains. Therefore, the basic
theory of mass flow modelling is reviewed. Subsequently, different extensions of
these concepts are presented. Although problems that are related with waste and
discarded products are often treated separately, the intention of this chapter is to
present these problems within a definite framework. This enables a better trade-off of
the effectiveness of definite measures.
From this, the following conclusions can be drawn:
 Better understanding of reuse and recycling requires modelling of product-process
chains. Such models encompass a number of companies.
 A standardised method of chain modelling exists. It can be restricted for products
other than complex consumer goods.
 In modelling, one should carefully pay attention to the definition of system
boundaries.
 The inadequate exchange of data between the different companies of the chain is a
major restriction on establishing optimal reuse/recycling chains.
 Shredder residue will become the principal problem when bans on landfill and
incineration of a large number of discarded tools and appliances are effectuated.
 Reducing the amount of shredder residue, the development of better, cheaper and
more adequate separation methods will only marginally contribute to this
problem.
 Product design should incorporate the minimisation of the amount of shredder
residue, both by enabling an enhanced disassembly depth and by establishing a
favourable materials composition.
15


Complex consumer goods represent, apart from cars, a relatively modest waste
stream. The challenge is its complexity in mechanical and chemical composition.
Life-cycle assessment, although internationally standardised, requires substantial
extensions in order to include recycling and reuse. The quantitative results of LCA
depend strongly on the extent of recycling that is practised. There is, however, not
a standardised method for modelling systems with recycle loops in LCA.
References
Graedel, T.E., and B.R. Allenby (1994) Industrial ecology, (Englewood Cliffs, NJ:
Prentice Hall).
Ayres, R.U., and L.W. Ayres (1996) Industrial ecology. Towards closing the
materials cycle, (Cheltenham, UK: Edward Elgar).
Erkman, S. (1997) ‘Industrial ecology: a historical view’ (with 150 references),
Journal of Cleaner Production, 5.1-2 :1-10.
Hart, S.L. (1997) ‘Beyond greening: strategies for a sustainable world’, Harvard
Business Review, 75.1: 66-77.
Veroutis, A.D., and J.A. Fava (1997) ‘Elements of effective DFA program
management and product stewardship’, Environmental Quality Management 7.1: 6170.
Sheng, P., and P. Worhach (1998) ‘A process chaining approach toward product
design for environment’, Journal of Industrial Ecology 1.4: 35-55.
Voet, E. van der, R. Kleijn, L. van Oers, R. Heijungs, R. Huele, and P. Mulder
(1995a) ‘Substance flows through the economy and environment of a region, Part I:
systems definition’, Environmental Science & Pollution Research 2.2: 90-96.
Voet, E. van der, R. Heijungs, P. Mulder, R. Huele R. Kleijn, and L. van Oers (1995b)
‘Substance flows through the economy and environment of a region, Part II:
modelling’, Environmental Science & Pollution Research 2.3: 137-144.
Lambert, A.J.D. (1999) ‘Linear programming in disassembly/clustering sequence
generation’, Computers & Industrial Engineering 36.12: 723-38.
Krikke, H.R., A. van Harten, and P.C. Schuur (1998) ‘On a medium term product
recovery and disposal strategy for durable assembly products’, International Journal
of Production Research 36.1: 111-39.
Guinée, J.B., H.A. Udo de Haes, and G. Huppes (1993a) ‘Quantitative life cycle
assessment of products, 1: Goal definition and inventory’, Journal of Cleaner
Production 1.1: 3-13.
Guinée, J.B., R. Heijungs, H.A. Udo de Haes, and G. Huppes (1993b) ‘Quantitative
life cycle assessment of products, 2: Classification, valuation and improvement
analysis’, Journal of Cleaner Production 1.2: 81-91.
Tillmann, A-M., T. Ekvall, H. Baumann, and T. Rydberg (1994) ‘Choice of system
boundaries in life cycle assessment’, Journal of Cleaner Production 2.1: 21-9.
Azapagic, A., and R. Clift (1999) ‘Allocation of environmental burdens in multiplefunction systems’, Journal of Cleaner Production 7: 101-19.
16
Table. List of symbols and abbrevations.
Symbol
Ag
Al
As
Au
Ba
Br
Cd
Cr
Cu
Fe
Hg
Mn
Ni
Pb
Pd
Pt
Sn
Zn
Abbreviation
BOM
CFC
ERP
ISO
LCA
LCD
PCB
X-ray
Chemical Element
Silver
Aluminium
Arsenic
Gold
Barium
Bromine
Cadmium
Chromium
Copper
Iron
Mercury
Manganese
Nickel
Lead
Palladium
Platinum
Tin
Zinc
Bill of Material
Chlorofluorocarbon (refrigerant)
Enterprise Resource Planning
International Organisation for Standardisation
Life-Cycle Assessment
Liquid Crystal Display
Printed Circuit Board
Roentgen rays
17
Figure 1. Aggregated linear product-process chain.
18
materials
recycling
EXTRACTION
MATERIALS
PRODUCTION
parts
reuse
PARTS
PRODUCTION
process waste
ASSEMBLY
CONSUMPTION
product reuse
REPAIR
DISASSEMBLY
FREEING
SEPARATION
DISCHARGE
Figure 2. Product-process chain for complex products, including reuse and recycling.
19
Figure 3. Scheme of mass and energy flows in a production process.
20
Figure 4. Convergence and divergence on the product and process level.
21
Figure 5. Tree structure of a typical LCA.
22
Figure 6. Example of a chain diagram with recycling.
23
Figure 7. Specific environmental impact of recycling vs. recycling degree.
24
Figure 8. Example of a chain diagram with recycling and exchange.
25