Life cycle assessment of wood wastes A case study of ephemeral by abstraks


									                                       Science of the Total Environment 357 (2006) 1 – 11

              Life cycle assessment of wood wastes: A case study
                            of ephemeral architecture
                        Beatriz Rivelaa, Marıa Teresa Moreiraa,*, Ivan Munozb,
                                            ´                       ´    ˜
                                                 b                     a
                                 Joan Rieradevall , Gumersindo Feijoo
Department of Chemical Engineering, University of Santiago de Compostela, C/ Lope de Marzoa s/n., E-15782 Santiago de Compostela, Spain
           Department of Chemical Engineering, Autonomous University of Barcelona, E-08193 Bellaterra (Barcelona), Spain
                                            Received 12 January 2005; accepted 1 April 2005
                                                     Available online 26 May 2005


    One of the most commonly used elements in ephemeral architecture is a particleboard panel. These types of wood products
are produced from wood wastes and they are used in temporary constructions such as trade fairs. Once the event is over, they are
usually disposed into landfills. This paper intends to assess the environmental effects related to the use of these wood wastes in
the end-of-life stage. The Life Cycle Assessment (LCA) of two scenarios was performed, considering the recycling of wood
waste for particleboard manufacture and energy generation from non-renewable resources (Scenario 1) versus the production of
energy from the combustion of wood waste and particleboard manufacture with conventional wooden resources (Scenario 2). A
sensitive analysis was carried out taking into account the influence of the percentage of recycled material and the emissions data
from wood combustion. According to Ecoindicator 99 methodology, Damage to Human Health and Ecosystem Quality are
more significant in Scenario 2 whereas Scenario 1 presents the largest contribution to Damage to Resources. Between the two
proposed alternatives, the recycling of wood waste for particleboard manufacture seems to be more favorable under an
environmental perspective.
D 2005 Elsevier B.V. All rights reserved.

Keywords: LCA; Wood; Ephemeral architecture residues; Energy emissions; Recycling

1. Introduction                                                            and processing of wood generates a variety of co-
                                                                           products and wastes throughout the wood processing
   Wood is the most important renewable material and                       chain, from its cultivation in forests, its extraction,
regenerative fuel (Bowyer, 1995). The management                           sawing and processing to intermediate and finished
                                                                           products, to its recycling, incineration or final dispos-
 * Corresponding author. Tel.: +34 981563100x16776; fax: +34               al. Co-products and wastes generated are residues
981547168.                                                                 from thinning, bark, sawdust, shavings, chips and
   E-mail address: (M.T. Moreira).                         fibers, side-cuts, wood waste and waste of intermedi-
0048-9697/$ - see front matter D 2005 Elsevier B.V. All rights reserved.
2                             B. Rivela et al. / Science of the Total Environment 357 (2006) 1–11

ate products from wood and wood-based industries                   methodology but the system boundaries are different,
(Jungmeier et al., 2002a,b).                                       results are not directly comparable. This fact could be
   It is evident that the huge utilization of wood as              considerably improved if the analyses defines a stan-
raw materials needs an appropriate management as a                 dard functional unit and special attention is paid to the
key action to optimize the use of resources and to                 management of the materials and how carbon fixation
reduce the environmental impact associated. Sustain-               on forestland is included (Jungmeier et al., 2002a,b).
able management of renewable resources is defined in                   The objective of this paper is to assess the envi-
a broad sense. One of the most widely accepted                     ronmental issues related to the use of wood wastes
definitions was set up in 1993 by the Ministerial                  derived from a worldwide used wooden product: par-
Conference for the Conservation of Forest in Europe:               ticle boards. These items are currently used in areas
bThe stewardship and use of forest and forest land in a            such as carpentry, building, furniture, and decoration,
way, and at a rate, that maintains their biodiversity,             among others. Temporary buildings such as trade fairs
productivity, regeneration capacity, viability and their           often use particle boards as a contemporary form of
potential to fulfill, now and in the future, relevant              architecture based on mobility and flexibility noted as
ecological, economic and social functions, at local,               ephemeral architecture. In this research study, one
national and global levels, and that does not cause                representative trade fair was analyzed in detail: the
damage to other ecosystemsQ (MCPFE, 1993; 2002).                   trade fair of Barcelona, with an annual waste genera-
   Based on the concept of sustainability, the equi-               tion of 8,000 tons, of which 70–80% are wood waste
librium between consumption of natural resources                   that are mainly disposed in landfills.
and their regeneration has to be encouraged. This
requires a more effective and efficient use of wood
including optimized process technology and products                2. Methodology
with longer service life and an aptitude for repairing,
material recycling and finally incineration with ener-                Life Cycle Assessment (LCA) is compiled of sev-
gy recovery (Lafleur and Fraanje, 1997). Reuse,                    eral interrelated components: goal definition and
recycling and energetic valorization of wood must                  scope, inventory analysis, impact assessment and in-
be considered since the material characteristics of                terpretation (ISO, 2000). SimaPro 6.1, which was
wood after the utilization phase still allow for a                 designed by Pre Consultant, is the software used in
variety of options such as material or energy carriers.                           ´
                                                                   this study (PRe-Consultants, 2004).
However, the more often the wood is reprocessed,
the more restricted are its potential applications.                2.1. Goal definition and scope
Besides, the investment of non-renewable energy
and material is necessary to restore physical–chemi-               2.1.1. Purpose
cal properties (Fraanje, 1997).                                       The goals of this study were to assess and compare
   The Life Cycle Assessment (LCA) methodology                     the environmental impacts of end-of-life scenarios of
has proved to be a valuable tool for documenting and               a product using LCA methodology. The two scenarios
analysing environmental considerations of product                  under study were (Fig. 1):
and service systems that need to be part of decision-
making process towards sustainability (Baumann and                  ! Scenario 1: Recycling of wood waste for particle-
Tillman, 2004). LCA has been already considered as                    board manufacture and energy production from
an important tool to evaluate the environmental im-                   non-renewable resources (i.e. natural gas).
pact of wood related products (Karjalainen et al.,                  ! Scenario 2: Energy production from the combus-
2001). Petersen and Solberg (2003) have published                     tion of wood waste and particleboard manufacture
an extensive review of several studies of LCA appli-                  with ordinary wooden resources.
cation to wood related products and, there, wood
appears to be not only a better alternative than other                The main objectives considered were the identifi-
materials but also competitive on price as a building              cation and quantification of the most important envi-
material. As the LCA studies have all used common                  ronmental burdens related to the alternatives under
                             B. Rivela et al. / Science of the Total Environment 357 (2006) 1–11                         3

                                        Particleboard with                 Conventional
                                        recycled material           +        energy

                                                     SCENARIO 1
      Wood Waste                                                                                          &
       Recovery                                                                                        Energy
                                                     SCENARIO 2

                                      Particleboard with no                 Energy from
                                        recycled material           +       wood waste

                             Fig. 1. Scheme of the scenarios analyzed for wood waste treatment.

analysis as a basis to discuss the final disposal of              systems (ISO, 2000). The system expansion allows
wood waste.                                                       the definition of an extensive functional unit that, in
                                                                  this study, can be delimited using allocation accord-
2.1.2. Functional unit                                            ing to one type of material use and energy from the
    This unit provides a reference to which the inputs            wood combustion (Jungmeier et al., 2002a). The two
and outputs are related (ISO, 2000). The twofold                  scenarios are described in Fig. 2, including their
nature of wood, commonly used as renewable mate-                  different subsystems. Depending on data availability,
rial or regenerative fuel, is a key aspect to be con-             a process analysis or an economic input–output ap-
sidered. System expansion and substitution are first              proach was considered to define the subsystems
priority strategies for dealing with multifunctional              under study. In both scenarios, the previous activities
situations. As a consequence of the system expan-                 of manufacture and use related to ephemeral archi-
sion, a variety of functions are added up to the                  tecture are assumed not to affect to the environmental
functional unit (Jungmeier et al., 2002a,b). Experts              burdens considered as we are studying an end-of-life
from industry stated that a recycling percentage of               phase (Boughton and Horvath, 2004). Infrastructures
30% would have no detrimental effect on the final                 were not taken into account according to the principle
quality of the board, which would result into a lower             of excluding identical activities for comparative
consumption of wood raw material from forest opera-               assessments (Consoli, 1993; Werner et al., 1997;
tions and sawmill. According to Jungmeier et al.                  Jungmeier et al., 2002a).
(2002a,b), a widespread functional unit was chosen,                  Scenario 1 includes the following subsystems:
considering both the possibility of material use and
energy recovery from wood combustion. Therefore, 1                 ! Collection of wood waste. The consumption of the
m3 of particleboard with 30% of recycled material                    forklift truck necessary for recollecting activities
(0.42 m3 of wood waste, calculated upon the wood                     was computed with an average value of 3.2 L of
raw materials substituted) in combination with the                   fuel per ton collected.
energy generated if the same quantity of wood waste                ! Transport and crushing. Wood waste has to be
is burned in a cogeneration unit for energy purposes                 crushed and transferred for further processing.
was the functional unit selected: 1 m3 of particle-                  Three alternatives were here considered (Fig. 3):
board along with 260 kWh of electricity and also                     Option A represents the existing management of the
1570 kWh of heat.                                                    fair, that is to say, transport of the waste to a
                                                                     recovery center in a semitrailer, off site crushing
2.1.3. System boundaries                                             and final transport for further processing; Option B,
   This term is defined as the interface between the                 proposed as an improvement action, takes into con-
product system and the environment or other product                  sideration the on site crushing and its further trans-
4                                 B. Rivela et al. / Science of the Total Environment 357 (2006) 1–11


                          SCENARIO 1                   ACTIVITIES I

                                                                                                                MANUFACTURE I

                                                  TRANSPORT & TRITURATING


                                                         FOREST                                                   PARTICLEBOARD
                                                       ACTIVITIES II                                              MANUFACTURE II

                          SCENARIO 2

                             Fig. 2. System boundaries and subsystems considered in the scenarios studied.

      port to be recycled or used as an energy source;                    hyde), mainly for indoor uses in which boards are
      Option C considers the transport of the waste to be                 neither exposed to high temperatures nor moisture
      crushed and processed in the particleboard or co-                   (ANSI, 1993). The inputs and outputs related to the
      generation plant. It is remarkable that the size of                 particleboard manufacture computing wood waste
      particle required for the recycling process is differ-              materials were included in the analysis.
      ent from the required size for cogeneration, al-                  ! Conventional energy. The comparison of the sce-
      though there are not significant differences in the                 narios requires the consideration of an equal energy
      energy consumption.                                                 generation in both scenarios. Based on the energy
    ! Forest activities I. The environmental loads associ-                generation from the incineration of the waste wood
      ated to both industrial wood and industrial residue                 flow (combustion of 0.42 m3 of wood waste), the
      wood were considered according to Ecoinvent da-                     cogeneration of 260 kWh of electricity plus 1570
      tabase (Werner et al., 2003). The consumption of                    kWh was considered using natural gas as fuel.
      wood per m3 particleboard is around 1.39 m3 of
      wood materials. As Scenario 1 considered a 30% of                   Scenario 2 comprises the following subsystems:
      recycled material from ephemeral architectural, the
      inventory data entail the activities related to 0.67 m3           ! Collection of wood waste. As it was previously
      of industrial wood and 0.30 m3 of industrial residue                defined in Scenario 1.
      wood, whereas 0.42 m3 of wood waste from the fair                 ! Transport and crushing. As it was previously de-
      fulfils the requirements of raw materials.                          fined in Scenario 1.
    ! Particleboard processing I. A particleboard is made               ! Forest activities II. As defined in Scenario 1, 0.96
      from small discrete wood elements with a water-                     m3 of industrial wood and 0.43 m3 of industrial
      resistant adhesive binder (usually urea formalde-                   residue wood were considered.
                             B. Rivela et al. / Science of the Total Environment 357 (2006) 1–11                       5

                                                                  OPTION A: off site

                               TRANSPORT            OFF SITE           TRANSPORT
                                   I               CRUSHING I              II

                             0.24 Ldiesel/ton•km 172.9 MJ/ton 0.02 Ldiesel/ton•km

                                                                  OPTION B: on site

                                      ON SITE                   TRANSPORT
                                     CRUSHING                       III

     Architecture                   4.6 Ldiesel/ton        0.02 Ldiesel/ton•km
     6,000 ton/year

                                                                  OPTION C: off site
                                     TRANSPORT                   OFF SITE
                                         IV                     CRUSHING II

                                0.24 Ldiesel/ton•km            172.9 MJ/ton

                                Fig. 3. Alternatives for transport and crushing of wood waste.

 ! Particleboard processing II. The inputs and outputs            (2003). The subsystems linked to forest activities,
   related to conventional particleboard manufacture              particleboard manufacture and energy cogeneration
   were included in the analysis. According to experts            scenarios are inventoried using data from the Ecoin-
   from industry, no significant differences related to                                                    ¨
                                                                  vent database (Werner et al., 2003; Fruhwald et al.,
   energy and additives consumption as well as emis-                        ¨
                                                                  1996; Fruhwald et al., 2001). The particleboard
   sions from the process were found between parti-               considered is for indoor use and includes the inputs
   cleboard processing I and II.                                  to the production processes, transport of those
 ! Bioenergy. A typical combined heat and power                   inputs and the process emissions (Werner et al.,
   plant (CHP) operating with biomass were consid-                2003).
   ered, with a standard ratio of electricity / heat of              The electricity profile is of major importance as it
   1 : 6. The cogeneration of 260 kWh of electricity              broadly affects the environmental impacts assigned
   plus 1570 kWh from wood waste combustion was                   to energy-consuming steps. The assignment of the
   considered.                                                    environmental loads associated to the different
                                                                  sources of electricity was made from BUWAL 250
2.1.4. Data quality                                               database (1996). According to data from the Insti-
   All the data related to the consumptions of the                tute for Diversification and Energy Saving (Spain):
subsystems of wood waste collection, transport and                35.8% of the electricity is produced from coal,
crushing were obtained from the company, which                    27.6% is nuclear, 13.9% is hydroelectric, 9.9% is
manages the wood waste from the Barcelona fair.                   obtained from oil power plants, 9.7% from gas
The assignment of the environmental loads associ-                 power plants, 2.2% from wind power plants, 0.6%
ated to these consumptions was made according to                  from waste use and 0.3% from biomass use (IDAE,
Kellenberger et al. (2003) and Spielmann et al.                   2004).
6                                  B. Rivela et al. / Science of the Total Environment 357 (2006) 1–11

2.1.5. Allocation                                                       2.2. Life cycle inventory
   Allocation is the apportioning of the input or out-
put flows of a unit process to the product system                          Life Cycle Inventory (LCI) analysis involves the
under study (ISO, 2000). The wood residues from                         collection and computation of data to quantify rele-
the trade fair, as they are considered waste from                       vant inputs and outputs of a product system, including
other activities, have no environmental burden alloca-                  the use of resources and releases to air, water and land
tion from previous processes and only their transport                   associated with the system (ISO, 2000). The inventory
and further processing were computed. Residues in                       data were collected for each process unit included
forest and in the wood industry taken into account for                  within the system boundaries. Data sources are indi-
particleboard manufacture, referred here as industrial                  cated in the data quality sub-section and they are
wood waste, are in fact by-products that can be used                    detailed in the results and discussion section.
as raw materials and fuel (i.e. edgings and chips
coming from sawmill). An economic allocation from                       2.3. Impact assessment
Ecoinvent database considering the wood resource,
CO2 absorption from air and the energy in biomass                           Impact assessment is a technical, quantitative and/
is used to assign the proper mass, energy and CO2                       or qualitative process to characterize and assess the
uptake from nature (Werner et al., 2003). It is remark-                 effects of the environmental burdens identified in the
able that allocation according to monetary value has                    Inventory (Consoli, 1993). Damage oriented impact
the fundamental disadvantage that market prices for                     assessment methodology has received attention in re-
forest products have a very volatile variation over                     cent years (Goedkoop and Spriensma, 2000; Hertwich
time, so it must be revised according to the short-                                                ¨¨        ¨ ¨¨
                                                                        and Hammitt, 2001; Seppala and Hamalainen, 2001;
term market disturbances.                                               Erlandsson and Lindfors, 2003). This approach pro-
                                                                        vides not only characterization (potential impacts of
2.1.6. Sensitivity analysis                                             impact categories such as climate change), but also
   To estimate the variability of the results obtained,                 damage assessment for safeguard subjects such as
two suppositions were considered:                                       human health (Goedkoop et al., 1998). This impact
                                                                        assessment was performed with the Ecoindicator 99
    ! Proportion of recycled material. Different percen-                methodology, which reflects the state of art in LCA
      tages of recycled material from 10% to 50% were                   (Itsubo, 2002). The inventory data are assigned to
      considered with the subsequent modifications of                   categories that represent basic environmental issues.
      the inventory data associated to the flows of raw                 Three conditions affecting human and environment are
      materials substituted.                                            considered: Human Health (HH), Ecosystem Quality
    ! Emissions data from wood waste combustions.                       (EQ) and sufficient supply of Resources (R). Model-
      There are various technical possibilities of energy               ling and estimation of an environmental indicator for
      generation from wood waste. Those aspects to be                   each category or issue are completed. Damages to HH
      taken into account for the analysis are the conver-               are expressed in Disability Adjusted Life Years
      sion efficiency from fuel to electricity and/or heat,             (DALY). Damages to EQ are expressed as Potentially
      the electricity / heat ratio, emissions to air (flue gas          Disappeared Fraction (PDF) and Potentially Affected
      cleaning system) and ash treatment (Jungmeier et                  Fraction (PAF) of species due to an environmental
      al., 2003). Three alternatives were analyzed con-                 impact. The PDF and PAF values are then multiplied
      sidering the effect of the cogeneration plant scale               by the area size and the time period to obtain the
      and the emissions to air. Bioenergy A involves a                  damage. Damages to R are expressed as the surplus
      cogeneration unit of 6400 kWth (option selected in                energy for the future mining of the resources.
      Scenario 2). The same unit is proposed in the
      Bioenergy B scenario with a stricter control of                   2.4. Interpretation
      emissions (filter for particulate matter and selective
      non-catalytic reduction for NOx). Bioenergy C                        The interpretation phase may involve the iterative
      corresponds to a cogeneration unit of 1400 kWth.                  process of reviewing and revising the scope of the
                              B. Rivela et al. / Science of the Total Environment 357 (2006) 1–11                       7

LCA, as well as the nature and quality of the data                 combustion of wood under a sustainable wood pro-
collected consistent with the outlined goal (ISO,                  duction might be CO2-neutral, but not CO2-free. En-
2000).                                                             ergy generation avoids natural oxidation (respiration)
                                                                   of biomass by emitting the same amount of CO2;
                                                                   therefore in a 50-years scenario the carbon cycle
3. Results and discussion                                          might be closed (Jungmeier et al., 2003).
                                                                      Wood combustion emissions have been shown in
3.1. Life cycle inventory                                          previous studies to be highly variable and dependent
                                                                   on many factors related to burning conditions, fuels
    The wood waste collection in the fair reveals a                and appliances (McDonald et al., 2000). Complete
consumption of 3.2 L diesel per ton collected. The                 combustion is difficult to obtain and it is rarely
main data of the subsystem covering transport and                  achieved; during incomplete combustion several
crushing activities are summarized in Fig. 3. Option A             harmful byproducts can be formed including polycy-
entails the transport of wood waste to a recovery                  clic aromatic hydrocarbons and particulate matter
plant, located 25 km far from the fair, by trucks                  (Kralovec et al., 2002). Moreover, there have been
with an average load of 2.5 tons; the wood waste is                many reports on formation of dioxins and dioxin-like
crushed with an electrical grinder and further trans-              compounds (polychlorinated dibenzofurans) (Yasu-
ported an average distance of 100 km to the particle-              hara et al., 2003). In this work, the module of inven-
board factory or the cogeneration unit by truck with               tory data for bioenergy describes the combustion of
an average load of 17 tons. The proposed Option B                  wood chips, including the infrastructure, the wood
comprises a transportable grinder with a processing                input, the emissions to air, the transport of fuel and
capacity of 100 tons a day, the consumption of crush-              the disposal of ashes. Inventory data also include the
ing and transport of the grinder covering a round trip             substances needed for operation: lubricating oil, urea,
of 50 km. In this case, crushed wood is transported to             organic chemicals, sodium chloride, chlorine and free-
the same destination that Option A (100 km approx-                 CO2 water. Data from Ecoinvent database have been
imately) by trucks with an average load of 17 tons.                considered to inventory cogeneration alternatives in
Option C entails the direct transport of wood waste to             order to make feasible a revision for all the readers
the particleboard factory or the cogeneration unit by              (Werner et al., 2003); nevertheless the complexity of
truck and further crushing there with an electrical                wood combustion should involve a more detailed and
grinder. The wastes coming from the crushing opera-                specific analysis of the operational conditions.
tion, mainly plastics, represent only the 3% of the
main flow. Emissions generated in the landfill are                 3.2. Transport and crushing: on site vs. off site
not considered since they do not significantly modify
the global results (Werner et al., 1997). Moreover,                   Fig. 4 shows the environmental fingerprint of
equal amounts of waste of the same composition are                 options A, B and C. The diagram represents a com-
treated in all scenarios, so the environmental burdens             parative analysis of the environmental advantages and
associated to their treatment can be rejected according            disadvantages of the three alternatives. For each cat-
to the principle of excluding identical activities for             egory, the characterization values were obtained and
comparative assessments (Consoli, 1993; Raynolds et                they are relatively compared, assigning a value b1Q to
al., 2000; Boughton and Horvath, 2004).                            the least favorable alternative in the category under
    It is assumed that wood particles for conventional             analysis. The possibility of crushing the wood waste
particleboard manufacture have to be taken from for-               in the particleboard or cogeneration plant involves a
estry and sawmill to satisfy the present demand of the             high capacity of transport, which leads to higher
particleboard industry (industrial wood and industrial             environmental burdens in all the categories analyzed.
residue wood, respectively). Emissions from the asso-              When comparing options A with B, it is observed that,
ciated activities were considered as well as the envi-             with the exception of the category of Ozone Layer, the
ronmental burdens allocated to edgings and chips                   results obtained show a significant improvement in
proceeding from sawmill. It is noteworthy that the                 the environmental performance of transport and crush-
8                                   B. Rivela et al. / Science of the Total Environment 357 (2006) 1–11

                                            RI                           categories of Carcinogens, Respiratory organics, Res-
                                                                         piratory inorganics, Climate change, Radiation and
                                                                         Ozone layer; damage to Ecosystem Quality is associ-
                                                        RO               ated to the categories of Ecotoxicity, Acidification/
                                                                         Eutrophication and Land use and damage to
                                                                         Resources is related to the categories of Minerals
                                                                         and Fossil fuels. The damage to Human Health is
                                                                         considerably higher in Scenario 2 (1.9 d 10À 4 DALY
                                                                         in Scenario 1 and 5.9 d 10À 4 DALY in Scenario 2).
                                                                         The damage to Ecosystem Quality is also favorable to
                                                         FF              Scenario 1 (37.3 PDF m2 year for Scenario 1 vs. 74.2
                                                                         PDF m2 year for Scenario 2). On the other hand,
          A/E                                                            Scenario 1 presents the largest contributions of dam-
                                             M                           age to Resource (782 MJ surplus in Scenario 1 and
                                                                         456 MJ surplus in Scenario 2).
Fig. 4. Environmental fingerprint of Option A vs. Option B. C:               The contribution of the different subsystems to the
Carcinogens; RO: Respiratory organics; RI: Respiratory inorganics;       total impact of each Scenario was analyzed in detail.
CC: Climate change; R: Radiation; OL: Ozone layer; E: Ecotoxicity;       The subsystems of bwood collectionQ and btransport
A/E: Acidification/Eutrophication; LU: Land use; M: Minerals; FF:
                                                                         and crushingQ are common for both scenarios and
Fossil fuels. Symbols: (n) Option A; (E) Option B; (x) Option C.
                                                                         present a minor contribution to the overall impact in
                                                                         most of the categories analysed (under 10%); only the
ing activities when Option B is considered (from 57%                     contributions of two categories are relevant: Ozone
to 80% for the categories analyzed). This fact is                        Layer (47.9% in Scenario 1 and 40.8% in Scenario 2)
explained in simple terms by the saving of diesel in                     and Acidification/Eutrophication (25.6% in Scenario
transport when the waste is crushed before being                         1 and 14.6% in Scenario 2). The main differences
transported. The use of electricity as energy source                     between the scenarios are explained by the reduction
for crushing would improve the environmental per-                        of the environmental impact caused by forest activities
formance but the available mobile grinder consumes
diesel as fuel.                                                                                     CC
   The Option B, corresponding to the optimized
subsystem of btransport and crushingQ, is suitable for                               R
both Scenario 1 and 2; thus, it is the option that will be
further considered in the next section.
3.3. Scenario 1 vs. scenario 2
   The analysis of the contribution of the different
subsystems to the impact categories is required to                           E
detect the bhot spotsQ. According to the accepted
LCA protocol of Ecoindicator 99, a methodical pro-
cedure for classifying and characterizing the types of
environmental effects of each element was performed
and potential environmental impacts were assessed                                                     LU
(Goedkoop and Spriensma, 2000; Rivela et al., 2004).
   The results for the characterization step are shown                   Fig. 5. Environmental fingerprint of Scenario 1 vs. Scenario 2. C:
                                                                         Carcinogens; RO: Respiratory organics; RI: Respiratory inorganics;
in Fig. 5. Considering the damage assessment as the                      CC: Climate change; R: Radiation; OL: Ozone layer; E: Ecotoxi-
computation of all the individual contributions of the                   city; A/E: Acidification/Eutrophication; LU: Land use; M: Minerals;
categories, damage to Human Health is related to the                     FF: Fossil fuels. Symbols: (E) Scenario 1; (n) Scenario 2.
                                                                     B. Rivela et al. / Science of the Total Environment 357 (2006) 1–11                                                       9

                                                                                    Percentage of recycled material
                    Climate Change Variation (DALY)•105         0%          10%             20%            30%             40%               50%
                                                          25                                                                                   25

                                                                                                                                                     Land Use Variation (PDF•m2yr)
                                                          20                                                                                   20
                                                          15                                                                                   15
                                                          10                                                                                   10
                                                           5                                                                                   5
                                                           0                                                                                   0
                                                           -5                                                                                  -5
                                                          -10                                                                                  -10
                                                          -15                                                                                  -15

Fig. 6. Climate Change and Land Use Deviation results for characterization in relation to percentage of material recycled (reference scenario:
30% material recycled). Symbols: (E) Climate Change; (n) Land Use.

in Scenario 1. However, it is remarkable that the use                                                     level of recycling. A percentage of 30% was selected
of natural gas for energy purposes instead of wood in                                                     as the representative of value considered in industry,
Scenario 1 turns into a significantly higher value for                                                    but different percentages in a range of 10–50% were
the category of Fossil fuels.                                                                             analyzed to evaluate the effect of this supposition.
   In order to discuss the obstacles and limitations of                                                      The results obtained for the characterization step of
this work, a sensitive analysis was carried out.                                                          Scenario 1 exhibit a minor influence of this topic for
                                                                                                          most of the categories studied with a deviation lower
3.3.1. Wood recycling ratios                                                                              than 5%. Obviously, the new scenarios have different
   Technologies available for recycling management                                                        inputs of natural gas, according to the energy gener-
were studied in order to establish the most adequate                                                      ated in each case if the same quantity of wood waste

Table 1
Characterization data of different scenarios for energy generation from 0.42 m3 of wood waste
Characterization step
Category                                                                   Unit                         Bioenergy A                 Bioenergy B                                      Bioenergy C
Carcinogens                                                                DALY.10   5                    4.40                        4.43                                                  4.76
Respiratory organics                                                       DALY.107                       1.27                        1.28                                                  1.36
Respiratory                                                                DALY.104                       3.37                        1.01                                                  7.60
Inorganics                                                                 DALY.105                       1.48                        2.43                                                  1.45
Climate change                                                             DALY.107                       1.49                        1.51                                                  1.66
Radiation                                                                  DALY.109                       2.27                        2.38                                                  2.65
Ozone layer                                                                PAF.m2yr                     162.00                      163.00                                                175.00
Ecotoxicity                                                                PDF.m2yr                       5.00                        4.94                                                  6.50
Eutrophication                                                             PDF.m2yr                      15.40                       15.50                                                 16.50
Land use                                                                   MJ surplus                     0.96                        0.98                                                  1.49
Minerals                                                                   MJ surplus                    19.40                       20.50                                                 23.00
Fossil fuel

Damage assessment
Human health                                                               DALY.104                        4.0                         1.7                                                   8.2
Ecosystem quality                                                          PDF.m2yr                       36.7                        36.8                                                  40.5
Resources                                                                  MJ surplus                     20.3                        21.5                                                  24.5
10                             B. Rivela et al. / Science of the Total Environment 357 (2006) 1–11

used in the particleboard manufacture was burned in a               leads to a significant reduction of the environmental
cogeneration unit; thus, characterization results for the           burdens of the process. As a first approach, the recy-
category of Fossil Fuels vary from 80.7 to 656.0 MJ                 cling of the wood waste for particleboard manufacture
surplus. Moreover, two categories show a significant                seems to be more favorable from an environmental
effect of recycled percentage: Climate Change and                   point of view. In this sense, alternative renewable en-
Land Use. Fig. 6 represents the variation (difference               ergies should be encouraged to avoid damage to
in relation to a scenario with 30% of recycled mate-                resources.
rial) of the characterization results according to the
percentage of recycled material considered. Increasing
the percentage of recycled material increases the con-              Acknowledgments
sumption of natural gas as well as reduces the assim-
ilation of CO2 from atmosphere from the raw                            This work was supported by the Galician Auto-
materials substituted, worsening the results of the                 nomous Government, Xunta de Galicia (Project
Climate Change category. On the other hand, Land                    references: PGIDIT04TAL262003PR and PGIDIT02-
Use category improves with the increase in recycling.               TAM26201PR).
3.3.2. Effect of energy emissions
   The results from the characterization step of the
three alternatives considered for the subsystem of                  References
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