Identifying Lowest‐Emission Choices and Environmental Pareto Frontiers for Wastewater Treatment Wastewater Treatment Input‐Output Model based Linear Programming

This article proposes a linear programming model that is based on the wastewater treatment input‐output model (W²IO) to identify the lowest‐emission choice among alternative feasible options for wastewater treatment; this model can be considered as an application of the waste input‐output linear programming model (WIO‐LP) to wastewater issues. Using the data of the Tokyo metropolitan W²IO table, I apply this model to obtain the optimal wastewater treatment options under alternative scenarios. The Pareto frontiers of environmental loads are derived to show the trade‐off relationships among various types of environmental load and the effect of the introduction of high‐temperature incineration of dewatered sludge on the generation of environmental loads. The main conclusion of the study is that when all three types of environmental load (landfill level, global warming potential, and chemical oxygen demand) are considered, the introduction of high‐temperature incineration causes the widening of the Pareto frontier of environmental loads and also causes it to move closer to the origin.     

The Waste Footprint of French Households in 2020: A Comparison of Scenarios of Consumption Growth Using Input‐Output Analysis

This study aims at quantifying and analyzing the waste footprint of French household consumption in 2020 with respect to different scenarios of economic growth. Three models are jointly used: (1) a multiregional unilateral input‐output model extended to waste, to quantify waste generation from economic activities induced by household consumption; (2) a coefficient‐based model dedicated to quantifying postconsumer waste as a function of household consumption; and (3) the New Econometric Model of Evaluation by Sectorial Interdependency and Supply (NEMESIS), a macroeconometric model used to elaborate different scenarios of growth in household consumption in the period 2008–2020. Three scenarios consider changes primarily in terms of household consumption volume, while one scenario additionally considers changes in the composition of consumption according to the past‐30‐year trend. First, this study suggests that if the trend in changes of composition is maintained, it will lead, by 2020, to a “relative” decoupling between French household consumption and waste footprint with respect to dry recyclables, mixed wastes, and organic wastes and to an “absolute” decoupling with respect to mineral wastes. Second, this study provides a mapping of the changes in French household waste footprints from 2008 to 2020 as a function of scenarios, with indications of where these changes would actually occur in the economy (waste from economic activities or postconsumer waste) and geographically (in France or abroad). In particular, for most of the scenarios considered, changes in French household consumption from 2008 to 2020 primarily induce changes in organic and mineral waste generation abroad rather than in France.     

A Supply‐Use Approach to Waste Input‐Output Analysis

In this article, we extend Namakura and Kondo's waste input‐output (WIO) framework by incorporating a supply‐use formalism, resulting in waste supply‐use tables (WSUTs). We present the theoretical underpinnings of the WSUT and, in particular, the transition from Nakamura and Kondo's WIO form to the new WSUT form. Further, we offer a mathematical proof of the equivalence of WIO and WSUT multipliers. We illustrate the workings of the WSUT calculus using economic and waste data for the Australian economy in 2008–2009.     

Input-Output Analysis of Waste Management

A new scheme of hybrid life-cycle assessment (LCA) termed the waste input-output (WIO) model is presented that ex-plicitly takes into account the interdependence between the flow of goods and waste. The WIO model has two distin-guishing features. First, it expands the Leontief environmental input-output (EIO) model with respect to waste flows. It turns out that the EIO model is a special case of the WIO model in which there is a strict one-to-one correspondence between waste types and treatment methods. By relaxing this condition, the WIO model provides a general framework for LCA of waste management. Second, the WIO model takes into account the "dynamics of waste treatment", which refers to the fact that the input-output relationships of waste treatment are significantly affected by the level and composition of waste feedstock, by incorporating an engineering process model of waste treatment. Because waste treatment is expected to accept whatever waste is generated by industry and households, a proper consideration of this feature is vital for LCA of waste management. We estimated a WIO table for Japan and applied it to evaluating effects of alternative waste management poli-cies with regard to regional concentration of incineration and the sorting of waste with regard to flammability. We found that concentrating treatment in a small number of large incin-erators combined with an increased degree of sorting could decrease both landfill consumption and the emission of carbon dioxide.     

An Input‐Output Model of Extended Producer Responsibility

Under an extended producer responsibility (EPR) system, when a producer delivers a product to the market it must also pay a takeback fee, which is used to cover the costs of end‐of‐life disposal. EPR systems are currently used in Europe and beyond to manage a variety of products, including packaging and used tires. In this article we develop an input‐output (IO) model that is able to assess the impacts of an EPR system, and is based on the waste IO (WIO) model. The WIO model is itself a hybrid‐unit model extension of the Leontief model that is able to capture the substitution effect between recycled/recovered material/energy from waste treatment and their non‐waste cognates. The resulting EPRIO model, besides the conventional direct and indirect effects of the Leontief model and the substitution effects of the WIO model, is able to capture the opportunity costs of financing the EPR system, and additionally requires the specification of an alternative waste management policy, with its own opportunity costs. The impact of an EPR policy is thus the difference between the impacts of the reference EPR and the alternative waste treament policies. The resulting model is illustrated with a simple example of a used tire management EPR system.     

An Australian Multi‐Regional Waste Supply‐Use Framework

The production of waste creates both direct and indirect environmental impacts. A range of strategies are available to reduce the generation of waste by industry and households, and to select waste treatment approaches that minimize environmental harm. However, evaluating these strategies requires reliable and detailed data on waste production and treatment. Unfortunately, published Australian waste data are typically highly aggregated, published by a variety of entities in different formats, and do not form a complete time‐series. We demonstrate a technique for constructing a multi‐regional waste supply‐use (MRWSU) framework for Australia using information from numerous waste data sources. This is the first MRWSU framework to be constructed (to the authors' knowledge) and the first sub‐national waste input‐output framework to be constructed for Australia. We construct the framework using the Industrial Ecology Virtual Laboratory (IELab), a cloud‐hosted computational platform for building Australian multi‐regional input‐output tables. The structure of the framework complies with the System of Environmental‐Economic Accounting (SEEA). We demonstrate the use of the MRWSU framework by calculating waste footprints that enumerate the full supply chain waste production for Australian consumers.     

Using an Industrial Waste Account to Facilitate National Level Industrial Symbioses by Uncovering the Waste Exchange Potential

The identification of potential by‐product exchanges is important for fostering industrial symbiosis. To discover these potential exchanges, this article extends the analysis of local industrial symbiosis to a national scale. A waste input‐output table, which is a material flow accounting tool, was compiled and used as a database to examine the existing exchanges of by‐products. The supplies and demands of industrial wastes or by‐products were compared to highlight their potential use for promoting higher exchange flows. The analysis of the linkages indicated that the majority of each of the by‐products were reused by the few industries that had the technology and operational capacity for reuse. This finding is useful for determining which industries are good candidates for promoting further industrial symbiosis (IS). Based on a nation‐wide analysis that considered the industrial characteristics of Taiwan comprehensively, 23 types of major by‐products with greater reuse flows and 216 potential exchange patterns were identified between the industries. In addition, three types of eco‐industrial networks were characterized as follows according to their dominant types: (1) fossil fuel, metal, and mineral‐dominated; (2) agricultural and synthetic material‐dominated; and (3) information and communications technology (ICT) and chemical industry‐dominated eco‐industrial networks. This analysis highlights the resource exchange potentials and provides information to new firms for networking with existing businesses.     

Evaluating the Use of Global Sensitivity Analysis in Dynamic MFA

Dynamic material flow analysis (MFA) provides information about material usage over time and consequent changes in material stocks and flows. In order to understand the effect of limited data quality and model assumptions on MFA results, the use of sensitivity analysis methods in dynamic MFA studies has been on the increase. So far, sensitivity analysis in dynamic MFA has been conducted by means of a one‐at‐a‐time method, which tests parameter perturbations individually and observes the outcomes on output. In contrast to that, variance‐based global sensitivity analysis decomposes the variance of the model output into fractions caused by the uncertainty or variability of input parameters. The present study investigates interaction and time‐delay effects of uncertain parameters on the output of an archetypal input‐driven dynamic material flow model using variance‐based global sensitivity analysis. The results show that determining the main (first‐order) effects of parameter variations is often sufficient in dynamic MFA because substantial effects attributed to the simultaneous variation of several parameters (higher‐order effects) do not appear for classical setups of dynamic material flow models. For models with time‐varying parameters, time‐delay effects of parameter variation on model outputs need to be considered, potentially boosting the computational cost of global sensitivity analysis. Finally, the implications of exploring the sensitivities of model outputs with respect to parameter variations in the archetypical model are used to derive model‐ and goal‐specific recommendations on choosing appropriate sensitivity analysis methods in dynamic MFA.     

An Analysis of Sustainable Consumption by the Waste Input-Output Model

The extension of the waste input-output (WIO) model to analyze households' sustainable consumption patterns is presented in this article. We estimate direct and indirect emission loads induced by household consumption by the WIO model. The WIO model is much more suitable for the analysis of sustainable consumption than the conventional input-output model because it can deal with the disposal stage of consumed goods as well as the purchase and use stages. A simple method for evaluating income rebound effects is also introduced. As indicators of environmental loads, we estimate carbon dioxide (CO₂) emissions and landfill consumption induced by household consumption. The model is applied to some typical sustainable consumption scenarios: shifting transportation modes from a private car to public transportation, the longer use of household electric appliances, and eating at restaurants instead of cooking at home. We found that the income rebound effects should be considered to evaluate environmental loads induced by different consumption patterns.     

Investigating Reasons for Differences in the Results of Environmental,Physical, and Hybrid Input‐Output Models

It is vital to find reasons for differences in the results of environmental input‐output (EIO), physical input‐output (PIO), and hybrid input‐output (HIO) models for industrial and environmental policy analysis. Using EIO, PIO, and HIO models, China's industrial metabolism is calculated. Four reasons were found to account for differences in the results of analysis using EIO, PIO, and HIO models: the manner in which they deal with residential consumption, service sectors, and waste recycling, and the assumption of unique sector prices. The HIO model, which treats residential consumption as sectors of the intermediate delivery matrix, is preferred to the EIO and PIO models for analyzing industrial and environmental policies. Moreover, waste recycling in five sectors—agriculture; the manufacture of paper, printing, and articles for culture, education, and sports activities; the manufacture of nonmetallic mineral products; smelting and pressing of metals; and construction—should be comprehensively considered when using the HIO model to study problems related to these five sectors. Improvements in the EIO, PIO, and HIO models and future work are also discussed.     

Waste treatment in product specific life cycle inventories

The final disposal of waste in sanitary landfills generates environmental impacts in the form of gaseous emissions and effluents in the seepage water. In product specific Life Cycle Assessments, these environmental impacts resulting from the disposal of the product under study frequently have a strong influence on the overall results. The Sanitary Landfill (SL), like the Municipal Solid Waste Incineration (MSWI), is a complex system with a large variety of different types of waste with varying input composition. A direct determination of the environmental impacts resulting from the landfilling of a single input component, e.g. by measurements, is not possible. The model approach described in this paper shows an operationalized concept for the allocation of the environmental effects caused by the landfill process to special input components. The calculation of the landfill emissions in the model is based on the emission spectrum (landfill gas and seepage water) of an average-sized landfill in Germany and the elementary composition of the single waste fraction under consideration. The resulting reactor landfill module comprises an average split for diffuse and captured landfill emissions, the use of captured landfill gases in a gas engine and a cleaning of captured seepage water in a waste water treatment plant. A short case study demonstrates the calculation of the effects of landfilling of a defined waste fraction (bottle fraction in post-consumer plastic waste).     

Waste treatment in product specific life cycle inventories

In product specific Life Cycle Assessment the environmental impacts resulting from the disposal of the product under study frequently have a strong influence on the overall result. Since the major disposal system - the Municipal Solid Waste Incineration (MSWI) and the Sanitary Landfill (SL) - are complex processes specially adapted for the treatment of a large variety of different types of waste with varying input composition, the direct determination of the environmental impacts coming from a single input component for example by measurements is not practicable. Two methods (Part I: MSWI, Part II: SL) of allocating the inventory positions caused by the processes MSWI and SL to individual input fractions are presented. The approaches described are based on process modelling for the calculation of the material and energy inputs and outputs of the disposal systems. For the MSWI process the material related allocation is carried out by means of a study of difference: The input/output balance is calculated with the process model for two variants with different input compositions. The input for the first variant consists of waste of average composition enlarged by a small amount of special waste fraction under study. In the second variant the calculation is done with an input consisting only of waste with average composition. The difference formed between the results of process calculation for both variants gives the effects of the treatment of the waste fraction under study in the disposal process.     

Hybrid LCC of Appliances with Different Energy Efficiency (10 pp)

Goal, Scope and Background This paper is concerned with a life cycle assessment (LCA) and life cycle costing (LCC) by the use of the waste input-output (WIO) quantity- and price model of air conditioners with different energy efficiency at the use phase (high-end, low-end and average models) that were available in Japan as of winter 2002. The functional unit is an air conditioner of the 2.5kW type that is used for 10 years, and then subjected to an end-of-life (EoL) process that is consistent with the Japanese law on the recycling of appliances. Methods This is the first simultaneous application of the WIO methodology to an LCA and LCC over the entire life-cycle of a product including the use phase, and represents a methodological extension (in the sense of considering the use phase) and integration (in the sense of a simultaneous application) of previous studies by us (Kondo and Nakamura, Int. J. LCA, 2004, Nakamura and Kondo, Ecol. Econ., 2005, in press). The main body of data is provided by the WIO table for the year 2000, an update of the previous table for 1995 that was used in the above WIO studies. Compared with the WIO table for 1995 that consisted of only about 80 industry sectors, the current one consists of about 400 industry sectors, and includes air conditioner as a separate sector. The data on the purchase price and efficiency of air conditioners indicate wide variations: the cheapest one (the low-end model) costs half of the most expensive one (the high-end model), but its efficiency is about half of the latter. Results and Discussion When the cost in the use and EoL phases is included, the low-end model becomes the most expensive one, and the high-end model with the highest purchase cost the least expensive. This reversal of the relative cost levels is attributed to the difference in the efficiency in the use phase. A sensitivity analysis indicates that a reduction of the electricity price in the use phase by about 40% does not alter the significant superiority of the high-end model over the low-end model. In spite of the largest amount of input in the production phase, the high-end model performs the best in terms of both global warming potential (GWP) and landfill, while the low-end model performs the worst. The use phase generates the largest amount of waste for landfill across the three models, the largest component of which is flyash generated from coal firing power plants. A possible internalization of externality in the form of carbon tax was found to work in favor of the high-end model. The cost advantage of the high-end model, however, is sensitive to the rate of discounting of future costs: discounting at 15% diminishes its advantage over the low-end model. Recommendation and Perspective The results indicate the effectiveness of the pricing based on the life cycle cost for achieving sustainability, that is, for promoting the shift of the demand away from appliances with low environmental performance to the one with higher environmental performance. Acceptance by society of pricing based on life cycle costing would require, among other things, an economy-wide standardization of the LCC concept (in a manner analogous to ISO-LCA) that can be used complementary to ISO-LCA.     

Waste Treatment and Assessment of Long-Term Emissions (8pp)

Goal, Scope and Background The disposal phase of a product’s life cycle in LCA is often neglected or based on coarse indicators like ‘kilogram waste’. The goal of report No. 13 of the ecoinvent project (Doka 2003) is to create detailed Life Cycle Inventories of waste disposal processes. The purpose of this paper is to give an overview of the models behind the waste disposal inventories in ecoinvent, to present exemplary results and to discuss the assessment of long-term emissions. This paper does not present a particular LCA study. Inventories are compiled for many different materials and various disposal technologies. Considered disposal technologies are municipal incineration and different landfill types, including sanitary landfills, hazardous waste incineration, waste deposits in deep salt mines, surface spreading of sludges, municipal wastewater treatment, and building dismantling. The inventoried technologies are largely based on Swiss plants. Inventories can be used for assessment of the disposal of common, generic waste materials like paper, plastics, packaging etc. Inventories are also used within the ecoinvent database itself to inventory the disposal of specific wastes generated during the production phase. Inventories relate as far as possible to the specific chemical composition of the waste material (waste-specific burdens). Certain expenditures are not related to the waste composition and are inventoried with average values (process-specific burdens). Methods The disposal models are based on previous work, partly used in earlier versions of ecoinvent/ETH LCI data. Important improvements were the extension of the number of considered chemical elements to 41 throughout all disposal models and new landfill models based on field data. New inventories are compiled for waste deposits in deep salt mines and building material disposal. Along with the ecoinvent data and the reports, also Excel-based software tools were created, which allow ecoinvent members to calculate waste disposal inventories from arbitrary waste compositions. The modelling of long-term emissions from landfills is a crucial part in any waste disposal process. In ecoinvent long-term emissions are defined as emissions occurring 100 years after present. They are reported in separate emission categories. The landfill inventories include long-term emissions with a time horizon of 60’000 years after present. Results and Discussion As in earlier studies, the landfills prove to be generally relevant disposal processes, as also incineration and wastewater treatment processes produce landfilled wastes. Heavy metals tend to concentrate in landfills and are washed out to a varying degree over time. Long-term emissions usually represent an important burden from landfills. Comparisons between burdens from production of materials and the burdens from their disposal show that disposal has a certain relevance. Conclusion The disposal phase should by default be included in LCA studies. The use of a material not only necessitates its production, but also requires its disposal. The created inventories and user tools facilitate heeding the disposal phase with a similar level of detail as production processes. The risk of LCA-based decisions shifting burdens from the production or use phase to the disposal phase because of data gaps can therefore be diminished. Recommendation and Perspective Future improvements should include the modelling of metal ore refining waste (tailings) which is currently neglected in ecoinvent, but is likely to be relevant for metals production. The disposal technologies considered here are those of developed Western countries. Disposal in other parts of the World can differ distinctly, for logistic, climatic and economic reasons. The cross-examination of landfill models to LCIA soil fate models could be advantageous. Currently only chemical elements, like copper, zinc, nitrogen etc. are heeded by the disposal models. A possible extension could be the modelling of the behaviour of chemical compounds, like dioxins or other hydrocarbons.     

Maintenance and Expansion: Modeling Material Stocks and Flows for Residential Buildings and Transportation Networks in the EU25

Material stocks are an important part of the social metabolism. Owing to long service lifetimes of stocks, they not only shape resource flows during construction, but also during use, maintenance, and at the end of their useful lifetime. This makes them an important topic for sustainable development. In this work, a model of stocks and flows for nonmetallic minerals in residential buildings, roads, and railways in the EU25, from 2004 to 2009 is presented. The changing material composition of the stock is modeled using a typology of 72 residential buildings, four road and two railway types, throughout the EU25. This allows for estimating the amounts of materials in in‐use stocks of residential buildings and transportation networks, as well as input and output flows. We compare the magnitude of material demands for expansion versus those for maintenance of existing stock. Then, recycling potentials are quantitatively explored by comparing the magnitude of estimated input, waste, and recycling flows from 2004 to 2009 and in a business‐as‐usual scenario for 2020. Thereby, we assess the potential impacts of the European Waste Framework Directive, which strives for a significant increase in recycling. We find that in the EU25, consisting of highly industrialized countries, a large share of material inputs are directed at maintaining existing stocks. Proper management of existing transportation networks and residential buildings is therefore crucial for the future size of flows of nonmetallic minerals.     

The Impact of Scale,Recycling Boundary,and Type of Waste on Symbiosis and Recycling

Innovative waste recycling through industrial processes such as industrial and urban symbiosis has long been practiced and recently received much attention in the field of industrial ecology, with researchers making efforts to identify key contributing factors to successful industrial symbiosis. By analyzing 88 sample recycling projects in 23 eco‐towns in Japan, this article focuses on the factors of project scale, recycling boundary, and types of waste in relationship to environmental benefits and operational performance. The results showed that larger eco‐towns achieved more savings of virgin materials and higher stability in operation. Large‐scale projects tended to locate closer to the users of recycled products than did small‐scale projects. For treating similar types of waste, projects producing recycled products for special users (e.g., feedstock to a blast furnace for iron production) tended to locate closer to the users than those not producing for special users. The type of waste had a strong effect on the savings of virgin materials and recycling boundaries, while local factors had significant impacts on operational performance. The results also showed that agglomeration did not significantly contribute to the environmental benefits or operational performance of eco‐town projects. Another finding was that national agencies were helpful for facilitating cross‐prefecture transportation and long‐distance transaction of wastes. Implications of the findings are also discussed.     

A Comparison of Two Methods to Conduct Material Flow Analysis on Waste Tires in a Small Island Developing State

The disposal of scrap tires is one of the biggest solid waste issues facing some small island developing states (SIDS) in the Caribbean. Dominica is a small Caribbean island nation that seeks to maintain its well‐founded image as the “Nature Island of the Caribbean.” The economy has seen a steadily increasing import of both tires and cars, with no mechanism for exportation of spent tires. This study used data gathered from both government and international sources to estimate the quantity of tires currently on the island and projected each year up to 2020 to determine potential reuse options. We performed a material flow analysis (MFA) using tire import, vehicle registration records, and projected per capita income to determine the expected accumulation of waste tires. Vehicle registration is expected to rise with the island's wealth, which will affect the annual flow of tires. Two methods were used to predict vehicle growth over time. Our analysis showed an average waste tire output from the economy of 47,000 to 50,000 passenger tire equivalents (PTEs) per year, or approximately 470 to 500 short tons per year of mass. Such an output does not justify large expenditures of tire shredding and processing equipment, but whole tire applications may be feasible as potential disposition options. The methods can be easily replicated to give low‐range and high‐range estimates of waste tires disposed in the environment.     

The Waste Input-Output Approach to Materials Flow Analysis

Abstract: A general analytical model of materials flow analysis (MFA) incorporating physical waste input-output is proposed that is fully consistent with the mass balance principle. Exploiting the triangular nature of the matrix of input coefficients, which is obtained by rearranging the ordering of sectors according to degrees of fabrication, the material composition matrix is derived, which gives the material composition of products. A formal mathematical definition of materials (or the objects, the flow of which is to be accounted for by MFA) is also introduced, which excludes the occurrence of double accounting in economy-wide MFAs involving diverse inputs. By using the model, monetary input-output (IO) tables can easily be converted into a physical material flow account (or physical input-output tables [PIOT]) of an arbitrary number of materials, and the material composition of a product can be decomposed into its input origin. The first point represents substantial saving in the otherwise prohibitive cost that is associated with independent compilation of PIOT. The proposed methodology is applied to Japanese IO data for the flow of 11 base metals and their scrap (available as e-supplement on the JIE Web site).     

Anthropogenic Carbon Stock Dynamics of Pulp and Paper Products in Germany

Carbon‐based materials (CBMs) for energetic and material purposes combine biogenic and anthropogenic carbon cycles. In the latter, numerous manufactured products with various in‐use lifespans accumulate as anthropogenic carbon stocks. Understanding the behavior of these stocks is an important requirement to estimate not only future waste amounts, source for secondary raw materials, but also the impacts and effects in carbon emissions and carbon management. Previous models have estimated material stock changes; however, a lack of research in carbon stocks is perceived. Moreover, studies follow in‐use lifespan estimation approaches, such as decay functions, which do not coincide with observed consumption and waste treatment patterns. In the first part of this article, we present a carbon stock‐flow model to analyze inter‐relationships between carbon flows and stocks from raw materials to waste treatment processes considering a consumer perspective, where the dynamics of anthropogenic carbon stocks are completely described. In the second part, we study the pulp and paper industry in Germany under a scenario approach to analyze the behavior, development, and impacts of paper stocks and flows between 2010 and 2040. The model provided coherent results, with industrial data estimating 33.9 million metric tons in 2010 in paper stocks, equivalent to 410 kilograms per person. Consumption per capita and in‐use lifespan of products were identified as the most significant variables in carbon stock building. Model simulations show a sustained growth in stocks for the next 30 years, with increase in waste and carbon emissions. But in combination with recycling and reuse mechanisms and consumption patterns, environmental impacts are reduced.     

Generalized Make and Use Framework for Allocation in Life Cycle Assessment

Allocation in life cycle inventory (LCI) analysis is one of the long‐standing methodological issues in life cycle assessment (LCA). Discussion on allocation among LCA researchers has taken place almost in complete isolation from the series of closely related discussions from the 1960s in the field of input?output economics, regarding the supply and use framework. This article aims at developing a coherent mathematical framework for allocation in LCA by connecting the parallel developments of the LCA and the input?output communities. In doing so, the article shows that the partitioning method in LCA is equivalent to the industry‐technology model in input?output economics, and system expansion in LCA is equivalent to the by‐product‐technology model in input?output output economics. Furthermore, we argue that the commodity‐technology model and the by‐product‐technology model, which have been considered as two different models in input?output economics for more than 40 years, are essentially equivalent when it comes to practical applications. It is shown that the matrix‐based approach used for system expansion successfully solves the endless regression problem that has been raised in LCA literature. A numerical example is introduced to demonstrate the use of allocation models. The relationship of these approaches with consequential and attributional LCA models is also discussed.