Evaluating Waste Management Strategies

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Resources, Conservation and Recycling 52 (2007) 103–118

Evaluating waste management strategies—Acase of metal-contaminated waste wood

J. Krook ∗, A. Martensson, M. Eklund

Environmental Technology and Management, Department of Mechanical Engineering,

Link¨ oping University, SE-581 83 Link¨ oping, Sweden

Available online 9 May 2007

Abstract

In Sweden recovered waste wood (RWW) is used for heat production, which reduces the share of

waste that is landfilled and recovers the energy content of the waste. However, this waste contains

contaminated materials that pollute RWW with heavy metals, causing downstream environmental

problems. The main objective of this study was to analyse how different upstream-oriented strategies

to manage RWW, influence the arising of environmental pressures downstream the waste management

system. Today, the contaminated materials in RWW are handled together with the main waste flow.

This upstream approach was compared with a separation strategy that removes contaminants from

the main waste flow thereby handling these materials separately downstream the waste managementsystem. An extended substance flow analysis (SFA) methodology that also includes resource issues

was applied for the analysis. The results show that the upstream separation strategy exhibits potential

environmental benefits. However, to accurately prevent environmental pollution also in a long time

perspective, upstream separation strategies must be combined with downstream measures aimed to

immobilise the contaminants in by-products. Otherwise, such separation strategies, as the current

handling of RWW, may cause temporal and spatial shifting of problems. To enable immobilising

measures, however, upstream separation strategies are important since they decrease the volume

problem.

© 2007 Elsevier B.V. All rights reserved.

Keywords: Waste management strategies; Heavy metals; Problem shifting; Substance flow analysis

∗ Corresponding author. Tel.: +46 13 288903; fax: +46 13 281399.

E-mail address: [email protected] (J. Krook).

0921-3449/$ – see front matter © 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.resconrec.2007.03.002

mailto:[email protected]

http://dx.doi.org/10.1016/j.resconrec.2007.03.002

http://dx.doi.org/10.1016/j.resconrec.2007.03.002

mailto:[email protected]



104 J. Krook et al. / Resources, Conservation and Recycling 52 (2007) 103–118

1. Introduction

Today, large amounts of material contaminated by hazardous substances have accumu-lated in the technosphere, posing environmental and health problems (Bergback et al., 2001;

Obernosterer and Brunner, 2001; van der Voet et al., 2000). Hence, to prevent dispersal of

hazardous substances into the environment, it is important to develop strategies for man-

aging these waste flows. A group of contaminants that is especially relevant in this respect

is that of heavy metals (Reijnders, 2000; Ayres, 1997). These toxic substances have been

frequently used in the technosphere and are non-degradable, which means that pollution of

the environment will be permanent.

To prevent emissions of hazardous substances during handling of waste flows, strate-

gies can be implemented at different locations of the waste management system (Fig. 1).

Downstream strategies are here characterised as measures taken from the treatment plant

and further downstream the system, e.g. gas and water cleaning, dilution measures, mon-

itoring and by-product management. These strategies have been commonly applied in the

past, but are also frequently implemented today, to decrease environmental pollution. The

focus of this study, however, is on the efforts taken before the waste arrives to the final

treatment plants, here called upstream strategies. Such strategies can be important since

they influence pre-conditions for further handling. There are two main upstream strategies

to handle contaminated waste flows: contaminants can be handled together with the waste

flow or removed and handled separately. Removing contaminants can be accomplished by,

for instance, separation at the waste generation site, i.e. source separation (cf. Ruch et al.,

1997; Thormark, 1995) or by waste separation technologies such as screening, air classifiers

and magnetic separators (cf. Schachermayer et al., 2000; Brunner and Stampfli, 1993).

Fig. 1. Characterisation of upstream and downstream strategies for abating emissions of hazardous substances

during management of contaminated waste flows. The dotted line shows the main strategies focused on in this

study.



J. Krook et al. / Resources, Conservation and Recycling 52 (2007) 103–118 105

In this study the effects of different upstream strategies was analysed by studying the

Swedish recovered waste wood(RWW) flowin detail. RWW mainly consists of construction

and demolition waste wood, but also of other discarded products such as packaging material(e.g. wood pallets) and furniture. The waste is mainly used as an energy source for district

heating plants, which reduces the waste volume and produces heat, thereby establishing an

economic outlet for the waste material. In Sweden, the energy retrieved from RWW is in the

order of magnitude of 1.5–2 TWh, which constitutes about 5% of the use of district heating

(Krook et al., 2004). However, RWW contains contaminated materials that pollute the waste

flow with heavy metals, causing downstream environmental and resource problems.

It is not self-evident that upstream strategies decrease the environmental impact (cf.

Raadschelders et al., 2003). For example, if the contaminated materials are removed from

thestudied waste flow, thequestionstill remains: how to handlethis highlypollutedmaterial?

Handling contaminated materials separately from the studied waste flow might cause similar

or other types of environmental impacts elsewhere in the economy, or else the problem can

be temporarily “solved” but re-appear in the future.

1.1. Objective and scope

Thisstudy takes a waste management perspective and comparesdifferent upstreamstrate-

gies to manage waste flows contaminated with heavy metals. Swedish RWW flows in the

year 2002 in the municipality of Norrk oping were assessed to exemplify the issues of this

topic. The main objective was to evaluate how different upstream strategies influence the

arising of pollution and resource problems downstream the waste management system.

2. The material and substance flows of Swedish RWW in Norrk opingmunicipality

The municipality of Norrk oping is located in the county of Ostergotland and covers

about 1500 km2. In number of inhabitants, it is the seventh largest Swedish municipality,

with approximately 120,000 citizens. Handelo thermal power plant (owned by Sydkraft

AB) is located just outside the city of Norrk oping and constitutes the main heat producer.

This plant has several boilers using different fuels: RWW, coal, rubber, forest residues and

municipal combustible waste. In 2002, Handelo plant generated about 1000 GWh of district

heating, 300 GWh of electricity and 130 GWh of steam for industrial use.

This study focuses on management of RWW originating from the Swedish economy.

Apart from Swedish RWW, the thermal power plant at Handelo also uses large amounts of RWW (60,000 tonnes) imported from Europe however this flow is not included in the study.

Approximately 8200 tonnes of RWW was generated in Norrk oping in 2002 (Fig. 2).

The main amount was combusted in the biofuel boiler at Handelo (7000 tonnes) and about

800 tonnesentered the municipal waste incinerator through mixed combustible waste. It was

estimated that less than 400 tonnes of wood was landfilled due to Swedish legislation for-

bidding the landfilling of combustible waste. Moreover, Handelo thermal power plant used

30,000 tonnes of regional RWW from the counties of Sormland, Halland, Vastergotland,

Ostergotland and Smaland. Altogether, about 37,000 tonnes of Swedish RWW was energy




Fig. 2. The approximate material flows (tonnes) of regional and local Swedish RWW in Norrk oping municipality

in 2002. aWeighed amounts at Handelo thermal power plant in Norrk oping municipality during 2002. This flow

constitutes the focus of the study. bEstimated amounts that are based on the distribution between combustion of

RWW as chips in biofuel boilers, combustion in a municipal waste incinerator, landfilling and reuse presented in

The Swedish Environmental Protection and Agency (1996). It has been assumed that less than 5% of RWW was

landfilled in 2002 in comparison to 10–15% in 1996. This is mainly due to the fact that Swedish legislation forbids

the landfilling of combustible waste.

recovered in the biofuel boiler, which generated about 110–115 GWh, i.e. about 10% of the

supply of district heating in Norrk oping. This flow of RWW generated 3500 tonnes of ash,which was disposed of in different kinds of landfills.

Swedish RWW generally contains elevated concentrations of arsenic, chromium, lead,

copper, zinc, mercury, nickel and cadmium (Krook et al., 2004). It was assumed that the

RWW used in the biofuel boiler at Handelo has similar heavy metal content. Thereby, the

annual flow of 37,000 tonnes of RWW corresponds to a heavy metal flow of about 24 tonnes

(Table 1). Krook et al. (2006) have estimated the contribution of heavy metal contamination

from different pollution sources occurring in RWW. These pollution sources explain the

main amounts of arsenic, chromium, copper, lead and zinc, but the sources for mercury,

cadmium and nickel are less well understood. On the other hand, the elevated concentrations

of mercury, nickel and cadmium are small in comparison to the other metals. The identified

pollution sources comprise about 20 wt% of the total RWW flow (Krook et al., 2006),surface-treated wood (STW) 15%, industrial preservative-treated wood (IPTW) 4% and

plastic waste (PW), iron and steel (GFS) and soil and concrete (SAC) about 1%.

3. Method

Here, the method used to evaluate the environmental importance of different upstream

strategies is presented. Firstly, we describe the characteristics of the current handling of




Table 1

The metal content in RWW and the total heavy metal flow due to the RWW flow of 37,000 tonnes

Metal Concentration inRWWa (mg/kg)

Factor of increasedconcentration in RWWb Amount per year

in Norrk opingc

(kg)

Estimated contribution of pollution sources occurring in

RWWd (kg)

As 53 1800 1960 IPTW, 1960

Cr 60 960 2220 IPTW, 1780; STW, 110; SAC, 40

Pb 33 480 1220 STW, 1010; PW, 130; SAC, 60

Cu 59 80 2180 IPTW, 1480; STW, 40; SAC, 70

Zn 440 50 16280 STW, 11400; GFS, 2280

Hg 0.06 40 2 STW, 0.4; SAC, 0.2

Ni 3.5 40 130 SAC, 12

Cd 0.5 10 20 STW, 5; GFS, 1

The contribution of heavy metals from identified pollution sources occurring in the RWW flow is also presented.

See text for explanation. Note: IPTW, industrial preservative-treated wood;STW, surface-treated wood;PW,plastic

waste; SAC, soil and concrete; GFS, iron and steel (mainly galvanised fastening systems).a Krook et al. (2004).b The factor of increased metal concentration in Swedish RWW is the ratio between the metal concentration in

waste wood and the concentration in Swedish stem wood of pine and spruce.c The total metal flow due to the flow of 37,000 tonnes of RWW has been calculated by combining data from

Fig. 1 and the median concentrations in Swedish RWW.d Krook et al. (2006).

RWW and of two developed scenarios involving an extended separation of contaminated

materials. Secondly, the methodology used to evaluate the environmental consequences of

applying different upstream strategies is presented.

3.1. Description of the reference case and the scenarios

The reference case corresponds to the current handling of RWW, where contaminants

are handled together with the main waste flow and treated in the biofuel boiler at Handelo

(Table 2). In contrast, two scenarios were developed that remove the identified pollution

Table 2

Structure of the reference case and the two scenarios applied in this study

Reference case Scenario I Scenario II

Efficiency of removing identified

pollution sources (%)

0 50 100

Combusted in the biofuel boiler at

Handelo (tonnes)

37000; 29710 other; 5550

STW; 40 PW; 1430IPTW; 40 GFS; 230 SAC

33360; 29710 other;

2775 STW; 20 PW;715 IPTW; 20 GFS;

115 SAC

29710; 29710

other

Combusted in a municipal waste

incinerator (tonnes)

2795; 2775 STW; 20

PW

5590; 5550

STW; 40 PW

Combusted in a destruction

incinerator (tonnes)

715; 715 IPTW 1430; 1430

IPTW

The reference case corresponds to the present handling of RWW, Scenario I assumes that identified pollution

sources are removed with an efficiency of 50% and Scenario II assumes an efficiency of 100% in removing

identified pollution sources.




sources in RWW upstream the waste management system. In Scenarios I and II, contam-

inated materials were assumed to be removed from the RWW flow by an efficiency of 50

and 100%, respectively. How the different waste materials would be managed downstreamin the scenarios was based on the structure of the waste management system in Sweden.

According to current legislation, it is forbidden to landfill combustible waste. Furthermore,

the stock of wood is the most energy-intensive material stock in Swedish buildings and

more than 70% of its embodied energy can be recovered (Roth et al., 2002). Consequently,

when wood material is discarded, it is important to recover the energy content of the waste

(cf. Ayres and Ayres, 1996). There are also several factors that today counteract other recy-

cling options, e.g. reuse and material recycling, such as the contamination of the waste

(cf. Krook et al., 2004), present demolition technologies (cf. Thormark, 1995) and the

absence of structured quality evaluation tools for wood waste (cf. Hansson, 1998). It was

therefore assumed that energy recovery is today the most likely alternative for discarded

wood.

From 2002, Swedish legislation classifies IPTW as hazardous that only can be treated

in plants with permission to combust such waste. In the Scenarios, 700–1400 tonnes of

IPTW would be treated in the destruction incineration plant at SAKAB in the county of

Narke. When removed from the RWW flow, STW and PW were estimated to be combusted

in municipal waste incinerators instead of in the biofuel boiler, and withdrawn GFS to be

material recycled. The remaining amount of RWW (referred to as “other” in Table 2) would

still be combusted in the biofuel boiler.

In the reference case and Scenario I, the generated ashes would be landfilled due to the

elevated metal concentrations. However, in Scenario II, the generated slag from the biofuel

boiler was assumed to be reused as filler material in earth construction. The probability of

this assumption is further discussed during the presentation of the results.

3.2. Methodology of the environmental evaluation

By applying a substance flow analysis (SFA) methodology (cf. van der Voet, 2002), the

heavy metal flows through and from the technosphere for the reference case and Scenarios

were followed. Environmental measures can lead to that the hazardous substances relocate

and/or temporarily re-accumulate in the technosphere (e.g. Raadschelders et al., 2003).

In addition, heavy metals are not biodegradable which means that if extracted from the

lithosphere they will remain in the technosphere or environment for a long time. Therefore,

the heavy metal flows for each of the strategies were interpreted within broad spatial and

temporal system boundaries.

One drawback of using SFA for evaluating different waste management strategies is theblindness for shifting of problems to outside of the studied substance flows (Bouman et al.,

2000). Hence, the environmental assessment in this study also involves resource aspects by

including issues regarding the net energy flow and management of generated by-products.

The differences in the energy flow for each case have been analysed by including the

efficiency of energy recovery of the different combustion plants, energy savings through

material recycling of removed iron/steel (mainly fastening systems) and energy savings in

Scenario II by reusing the generated slag in earth construction. The energy flow due to

transport and waste processing of RWW was not included in the energy analysis, since




these were estimated to be of similar magnitude in all cases. The main amount of RWW

usedat Handelo is already transported long distances to Norrk oping from the southern parts

of Sweden. It is therefore not plausible that the removed contaminated materials will betransported longer distances to municipal waste incinerators and the destruction plant at

SAKAB. However, the significance of changed transport distances is further discussed in

the interpretation of the results.

From a resource perspective, reuse of by-products decrease the demand for landfill

space and replaces extraction of natural filler materials such as crushed rock and natural

gravel. Evaluating the environmental compliance of the generated ashes was performed by

calculating the concentrations and total flows of the studied metals and comparing these

with the content in natural filler materials, e.g. crushed rock, natural gravel and moraine. To

decrease the sources of error that origin from different elemental analysing techniques, the

content of metals in natural materials was retrieved from a study (Research for a Low-Waste

Ecocyclic and Society, 1999) that used the same dissolving and analysing methods as were

used to characterise the metal content of RWW (Krook et al., 2004). It should, however,

be mentioned that this methodology only generates a rough estimate for the quality of by-

products since it mainly considers total concentrations of hazardous substances (cf. Roth

and Eklund, 2003; Mroueh et al., 2000).

To address the total flow of metals and the concentrations in the ashes, several data

sources have been applied: the concentration of heavy metals in Swedish RWW (Krook

et al., 2004), the contribution of heavy metals from the identified pollution sources in

RWW (Krook et al., 2006), the amount of generated slag and fly ash from the biofuel

boiler at Handelo in 2002, and the heavy metal distribution to air, water, slag, and fly

ash during treatment in the biofuel boiler at Handelo (Ortenvik, 1999), municipal waste

incinerators (Bjorklund, 1998) and the destruction plant at SAKAB. It was not possi-

ble to get specific data on the distribution of heavy metals for the destruction plant atSAKAB. Instead, distribution data was taken from another incinerator plant at Savenas

with permission to combust industrial preservative-treated wood (SWECO, 1999). It was

assumed that the emissions to air and water for these two plants were of a similar order of

magnitude.

RWW has a calorific value of approximately 3.5 MWh per tonne and the energy recovery

efficiencies of the biofuel boiler at Handelo, waste incinerators and the destruction plant

at SAKAB are about 85, 85 and 80% efficient, respectively. Furthermore, it was assumed

that the recycled iron/steel in Scenarios I and II, i.e. 20–40 tonnes (Krook et al., 2006),

would replace virgin iron/steel corresponding to an energy saving of 3.5 MWh per tonne

of recycled iron/steel (Levine et al., 1995). Reusing the slag in earth construction replaces

virgin filler material. In Norrk oping municipality it is most likely that crushed rock isreplaced by the slag (cf. SGU, 2002). However, some of the slag might replace the use of

lightweight filler materials such as light expanded clay aggregate (LECA), due to its low

price. Two assumptions were applied for the energy savings accomplished by reusing slag

in earth construction in Scenario II: the slag replaces crushed rock and 90% of the slag

replaces crushed rock and 10% replaces LECA. Slag from RWW combustion at Handelo,

crushed rock and LECA have densities of about 1.2, 1.9 and 0.5 tonnes/m3, respectively.

Hence, 1 tonne of slag used as filler material replaces about 1.5 tonne of crushed rock and

0.4 tonne of LECA.




4. Results

4.1. The metal flow related to the RWW flow in Norrk¨ oping municipality

Today, the identified pollution sources are handled together with the RWW and treated in

the biofuel boiler at Handelo. This handling causes emissions of roughly 400 kg of metals,

comprising 2% of the total metal flow (Fig. 3). Removing the identified contaminated

materials from the waste flow and handling these materials separately downstream the

current waste management system substantially decreases the emissions during energy

recovery. In Scenarios I and II, the emissions of arsenic, chromium, zinc, lead and copper

are decreased by 40–80, 40–80, 30–60, 50–95 and 30–70%, respectively. Pollution sources

for nickel, cadmium and mercury are less well understood. Thus, the upstream separation

strategy applied in the scenarios probably does not remove these contaminants efficiently

from the waste combusted in the biofuel boiler. The emissions of cadmium decrease by

10–20% and for nickel and mercury the emissions are approximately similar for both of the

analysed upstream strategies. Altogether, the emissions of metal during energy recovery

would decrease by about 40 and 70% for Scenarios I and II, respectively.

For both of the studied upstream strategies the main flow of metals ends up in landfills,

for which zinc constitutes the main amount. If the pollution sources are efficiently separated

from the RWW flow, as in Scenario II, roughly 50% of the metal flow is redirected from

the biofuel boiler to municipal waste incinerators. Furthermore, in Scenarios I and II the

arsenic, chromium, and copper flows are redirected from landfills to the hazardous waste

storage at SAKAB. With an efficient removal of mainly IPTW, about 95, 80 and 70% of

the total metal flows of arsenic, chromium and copper ends up at the storage for hazardous

waste. In addition, reusing generated slag from the biofuel boiler in Scenario II would lead

to 600 kg of the total metal flow being redirected from landfills to earth construction. Forcomparison, if the slag would be reused today about 4000 kg of the total metal flow ends

up in earth construction.

4.2. Concentration of heavy metals in the generated ash from the biofuel boiler

Although the fly ash concentrations are substantially decreased in Scenario II, for most of

the metals they are still much higher than the concentrations in natural materials ( Table 3).

Today, the arsenic, chromium, copper and lead concentrations in the slag are higher than in

natural materials. For zinc, nickel, cadmium and mercury the concentrations in the slag are

within, or even lower than, the concentrations in natural materials. Despite the removal of

50% of the identified contaminated materials in Scenario I, the concentrations in the slag of arsenic, chromium, copper and lead are still higher than in natural materials. However, high

efficiencies of removing contaminated materials lead to concentrations within the range of

that in natural materials.

4.3. Total energy flow

ThemainenergyflowrelatedtotheflowofRWWinNorrk oping is due to energy recovery,

and thus the energy content of the wood material (Table 4). Energy savings accomplished






Table 3

Calculated concentration of heavy metals in residual products (mg/kg dry matter) from the biofuel boiler at Handelo

for the reference case (R. case) and Scenarios (I) and (II), respectively, assuming that 100% of the fuel comprised

RWW, which was the case at Handelo in 2002

Metal Slag, R. case Slag, I Slag, II Fly ash, R. case Fly ash, I Fly ash, II Concentration

in natural

materialsa

As 140 80 0.1 3,910 2,140 2 4.3–68.7

Cr 520 330 80 1,670 1,040 260 39.8–121

Zn 120 70 20 46,640 29,560 8,830 39.2–224

Cu 290 200 90 3,480 2,380 1,050 15.9–92.7

Pb 150 90 2 2,180 1,210 30 6.4–59

Ni 30 30 30 110 120 120 8.7–60.3

Cd 0.03 0.03 0.03 60 50 50 0.08–0.7

Hg 0.02 0.02 0.02 6 5 5 0.04–21

Concentrations in natural materials (mg/kg dry matter) are also shown. The by-products generated at the biofuelboiler comprise roughly 80 and 90% of the total amounts of by-products in Scenarios I and II, respectively.

a Range of the concentration of metals in rock, gravel and moraine ( Research for a Low-Waste Ecocyclic and

Society, 1999).

by recycling the removed amounts of iron/steel and reusing the ashes in earth construction

are of minor importance.

In Scenarios I and IIc, the net energy yield is slightly decreased (by 0.05%) compared to

the reference case, due to lower energy recovery efficiency of the destruction plant where

IPTW is combusted. However, in Scenario IId an increase in the net energy yield emerges by

replacing extraction of natural filler material and Leca with slag from the biofuel boiler. The

larger energy savings in Scenario IId are due to the fact that 10% of the slag is assumed to

replace LECA, which is quite an energy-intensive material (Svensk Leca, 2000). Altogether,the results show that the total energy yield is approximately the same for the reference case

and the scenarios, apart from minor differences.

Table 4

Differences in the energy yield for the reference case and Scenarios I and II, respectively

Case Energy recoverya

(MWh)

Energy savings from

recycling of iron/steelb

(MWh)

Energy savings from

reuse of ashes (MWh)

Total energy yield

(MWh)

Reference case 110,080 – – 110,080

Scenario I 109,950 70 – 110,020

Scenario IIc 109,820 140 50 110,010

Scenario IId

109,820 140 170 110,130The processes included are energy recovery, energy savings by recycling removed iron/steel in Scenarios I and II

and energy savings by reusing the generated ashes in earth construction in Scenario II.a Calculated from the calorific value of RWW of 3.5 MWh per tonne and the energy recovery efficiencies of the

biofuel boiler, municipal waste incinerators and the destruction plant of 85, 85 and 80%, respectively.b Based on data presented in Levine et al. (1995).c The generated slag at the biofuel boiler is reused in earth construction and replaces the extraction of crushed

rock. Energy savings by replacing crushed rock comes from Stripple (1995).d Ninety percent of theslag replaces crushed rock and 10% replaces light expanded clay aggregate (LECA) filler

material. Energy savings through replacing LECA comes from Svensk Leca AB (2000).




5. Interpretation of the results

There are mainly two approaches for managing hazardous substances occurring in wasteflows (cf. Guinee et al., 1999). The outflow from the technosphere can be delayed by, for

example, recycling of by-products or applying end-of-pipe measures such as water and gas

cleaning. Finally, the outflow can be controlled, e.g. by immobilisation and disposal outside

of the biosphere, to ensure that it does not reach sensitive environmental areas.

By separating pollution sources and the main RWW flow upstream the waste manage-

ment system, the emissions of heavy metals during energy recovery can be decreased. This

effect could, however, also be achieved by implementing measures further downstream

the waste management system. Both installation of additional gas and water cleaning at

the biofuel boiler and landfilling of the identified pollution sources would delay the out-

flow. However, landfilling would lead to that about 20% (21,000 MWh) less energy from

the RWW flow would be recovered. From a resource perspective, such strategy would

be problematic and the environmental benefit achieved most doubtful (cf. Roth et al.,

2002; Ayres and Ayres, 1996). In addition, Swedish legislation forbids landfilling of com-

bustible waste, so landfilling of RWW is not seen as an appropriate waste management

alternative.

Regardless of upstream handling strategy (the current handling or the separation strat-

egy), the main amount of heavy metal ends up in different kinds of landfills. Accordingly, in

a longer time perspective, the pollution problem still remains for most of the studied metals

(cf. van der Voet et al., 2000; Guinee et al., 1999; Flyhammar, 1997) (Table 5). However, for

arsenic, chromium, and copper the upstream separation strategy not only delays the outflow

but more importantly also increases the possibility of controlling the final outflow. The main

flows of arsenic, chromium and copper are redirected from different types of landfills to a

monitored storage of hazardous waste. This waste storage is designed and constructed toretain the hazardous substances, in comparison to landfills for which the operation and con-

struction varies widely (cf. Flyhammar, 1997). In addition, the separation strategy thereby

also decreases the number of sites for accumulation of these metals in the technosphere.

It can be argued that improving the management of the arsenic flow related to RWW is of

high environmental concern. This flow is, in contrast to the other studied metals, of a similar

magnitude as other identified large arsenic flows in Sweden such as a contaminant in coal

(Krook et al., 2004).

If efficiently implemented, the separation strategy redirects approximately 50% of the

heavy metal flow from the biofuel boiler to municipal waste incinerators, mainly through

surface treated wood. It could thereby be argued that thecurrent lead andzinc emissionsfrom

energy recovery of RWW partially are abated at expense of an additional contamination of municipal waste incinerator ashes, preventing reuse of these by-products. However, today

generated ashes from combustion of municipal solid waste are landfilled. In addition, this

waste flow already is polluted, especially of lead and zinc, thereby it is not, at present, likely

that this shifting of problem would occur (cf. Bergback, 1998). However, if the management

of municipal solid waste is improved in the future and generated ashes are aimed for reuse,

such shifting of problem may become a relevant environmental issue.

From a heavy metal pollution perspective, the upstream separation strategy establishes

important contributions to the current downstream focus on managing RWW. Firstly, it




Table 5

Comparison between the reference case, where contaminated material is handled together with the main waste

flow, and the scenarios, which correspond to an extensive separation of the polluted material and the waste flow,

upstream the waste management system

Environmental and resource

issue

Scenario I Scenario II

Short-term

perspective

Long-term

perspective

Short-term

perspective

Long-term

perspective

Pollution perspective

As, Cr and Cu + + ++ ++

Zn, Pb and Cd + 0 ++ 0

Hg 0 0 0 0

Ni 0 0 0 −

Total metal flow ++ + +++ ++

Resource perspectiveReuse of by-products

Decreased demand for

landfill space

0 +

Replacing extraction of

non-renewable

resources

Energy 0 0

The evaluation is done based on the present waste management system in Sweden. A plus sign (+) indicates

environmental advantages, whereas a minus sign (−) shows disadvantages compared to the reference case (0).

See text for further explanations.

delays the outflow by enabling energy recovery of the contaminated material in moresophisticated combustion plants thereby offering time to develop strategies to manage the

polluted residue products (cf. Guinee et al., 1999). Secondly, the upstream separation strat-

egy enables to decrease the number of accumulation sites for some of the contaminants and

to store these at a sophisticated waste plant thereby increasing the control of the outflow.

However, to accurately prevent environmental pollution, also in the long time perspec-

tive, upstream separation strategies must be combined with downstream measures aiming

to immobilise (e.g. Park and Heo, 2002; Park, 2000) these substances. To enable such

immobilising measures, upstream separation strategies are important since they decrease

the volume problem.

From a resource perspective, reuse of ashes is advantageoussince it decreasesthe demand

for landfill space and extraction of non-renewable resources. However, an extensive reuseof such by-products may also limit the ability to control outflows of heavy metals since

they become re-dispersed back into the technosphere. In this study, we have showed that

environmental compliance of the ashes generated during energy recovery of RWW can be

substantially increased by the upstream separation strategy. In order to obtain by-products

with heavy metal concentrations similar to those in natural materials, an efficient separation

of the identified pollution sources is probably necessary. It should, however, be noted that

this study assumes that the biofuel boiler uses solely RWW as fuel. In Sweden, plants using

RWW sometimes dilute this fuel by other biofuel thereby decreasing, for instance, opera-




tional problems (c.f. Andersson and Tullin, 1999). Other biofuels such as forest residues

contain less heavy metal than RWW whythe calculated concentrations in theashespresented

in this study shall be regarded as a worst-case scenario.When evaluating reuse of by-products it is important to not only consider concentrations

but also to discuss the total metal flows and final sinks (cf. Obernosterer and Brunner,

2001). At present, the generated slag from the biofuel boiler contains approximately 20%

of the total metal flow in RWW. However, if the identified pollution sources were efficiently

separated, only a minor share of this flow (2%) would end up in earth constructions due to

reuse of the slag.

It must be stated that the evaluation of the environmental compliance of residue products

accomplished in this study is restricted, i.e. only compares the concentration and total

metal flows. To accomplish a full-mode investigation of the environmental compliance

of residue products, several assessment levels probably must be taken into account (cf.

Roth and Eklund, 2003; Mroueh et al., 2000). Further on, the heavy metal distribution

between fly ash and slag during combustion in different biofuel boilers varies depending

on, for example, the combustion temperature, type of cleaning devices installed, type of

metal and the geometry and construction of the boiler (Maartmann and Lundqvist, 1998).

Consequently, the concentrations of heavy metals in ashes generated by different biofuel

boilers vary. However, the key point of this study is that a removal of a few pollution sources

upstream the waste flow, i.e. mainly IPTW and STW, enables to reuse the main amount of

generated slag without risking to re-disperse substantial amounts of the heavy metal flow

back into the technosphere.

The energy analysis is comparative, which means that activities that are assumed to be

approximately similar for the reference case and the scenarios are excluded, i.e. transport.

Furthermore,it is extremely hard to estimate thetransport distancessince thebiofuel boilerat

Handelo uses RWW originating from several different areas of southern Sweden. However,if assuming that RWW generally is transported about 200 km and the transport distances of

removed contaminated materials in Scenario II areeither 100 km or 300 km,the difference in

the energy flow with respect to transport becomes±130 MWh (NTM, 2003). Consequently,

transportation only constitutes about 0.1% of the total energy flow, which can be regarded

as negligible.

The major energy flow is related to the energy recovery process, and thus, the

energy content of the wood material. Hence, only minor differences occur between the

reference case and the scenarios, since the energy content of the waste is recovered

downstream the system. It can be concluded that an extended reuse of the ashes only

briefly influences the total energy flow. Thus, in the system analysed, the main resource

benefits achieved by reusing the ashes in earth construction are not related to energysavings but to reducing the demand for landfill space and extraction of non-renewable

resources.

This study has focused on the final handling of RWW, assuming that the waste is energy

recovered. However, in Sweden and other members of the European Union, there is an

increased interest in accomplishing a more efficient use of resources. A prerequisite to

increasing the resource efficiency by, for instance, applying “high quality” waste man-

agement options, e.g. reuse or material recycling, is to establish strategies to manage the

related substance flows (c.f Lindqvist, 2002; Reijnders, 2000). Upstream separation strate-




gies increase the possibility of applying “high quality” waste management options to the

main RWW flow in the future, without risking an extensive re-dispersion of hazardous

substances back into the technosphere.

6. Conclusions

The main conclusions from this study are summarised below:

• Implementing the upstream separation strategy to the current downstream focused man-

agement of RWW would decrease the emissions of heavy metal from energy recovery.

However, a potential disadvantage with this strategy is that some of the substance flows

become re-directed, and thereby, may influence management of other waste flows in the

future, e.g. municipal solid waste.

• For arsenic, chromium and copper, the upstream separation strategy also increases thecontrol of the outflows from the main amounts accumulated in by-products. At present,

however, implementation of separation strategies would for most of the studied metals

shift the pollution problem to the future. To accurately prevent environmental pollution

also in the long time perspective, upstream separation strategies therefore must be com-

bined with downstream measures, aiming to immobilise the hazardous substances. To

enable such downstream measures, upstream separation strategies are important since

they decrease the volume problem.

• From an energy perspective, as long as the energy content of the waste is recovered, the

influence of the studied upstream strategies has minor importance.

• The upstream separation strategy increases the environmental compliance of generated

residue products fromenergy recovery. Furthermore, it enables application of high qualityrecycling options, e.g. material recycling, to the main waste flow without risking to

re-disperse significant amounts of hazardous substances back into the technosphere.

Acknowledgement

Financial support from the Swedish Council for Environmental, Agricultural Sciences

and Spatial Planning (FORMAS) is gratefully acknowledged.

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Evaluating Waste Management Strategies