Biomass is the world’s largest renewable energy source, accounting for approximately 10% of global primary energy supply, and 5% of energy consumed in the United States. Prominent national programs like the U.S. Renewable Fuel Standard incentivize increased use of biomass, primarily as a transportation fuel. There has been comparatively little government support for using biomass as a renewable feedstock for the chemical sector. Such asymmetry in incentives can lead to sub-optimal outcomes in the allocation of biomass toward different uses. Greenhouse gas reduction is among the most cited benefits of bioenergy and bio-based products, however, there is increasing controversy about whether increased use of biomass can actually contribute to greenhouse gas emission targets. If biomass is to play a role in current and future greenhouse gas mitigation efforts its use should be guided by efficient use of natural and economic resources. This thesis addresses these questions through a series of case studies, designed to highlight important tradeoffs in the use of biomass for greenhouse gas mitigation. Should biomass be used as a fuel, a chemical feedstock, or neither? The first case study in this thesis focuses on the ‘fuel vs feedstock’ question, examining the greenhouse gas implications of expanding the scope of the U.S. Renewable Fuel Standard to include credits for bioethylene, an important organic chemical readily produced from bioethanol. Results suggest that an expanded policy that includes bioethylene as an approved use for ethanol would provide added flexibility without compromising greenhouse gas targets – a clear win scenario. Having established that bioethylene based plastics can achieve similar greenhouse gas reductions to bioethanol used as fuel, this thesis expands the analysis by considering how the greenhouse gas emissions from a wider range of bio-based plastics compare to each of the main commodity thermoplastics produced in the U.S. The analysis demonstrates that there are large uncertainties involved in the life cycle greenhouse gas emissions from bio-based plastics, and that only a subset of pathways are likely to be preferable to conventional plastics. The following chapter then builds on the existing model to compare the greenhouse gas mitigation potential of bio-based plastics to the potential for reducing emissions by adopting low carbon energy for plastics production. That chapter concludes that switching to renewable energy across the supply chain for conventional plastics energy cuts greenhouse gas emissions by 50-75%, achieving a greater reduction, with less uncertainty and lower cost, than switching to corn-based biopolymers – the most likely near-term biopolymer option. In the long run, producing bio-based plastics from advanced feedstocks (e.g. switchgrass) and/or with renewable energy likely offers greater emission reductions. Finally, this thesis returns to the dominant form of policy surrounding biomass use: biofuel mandates. That study takes a consequential approach to the ‘fuel or neither’ question. Specifically, this work examines how petroleum refineries are likely to adjust their production in response to biofuel policies, and what this implies for the success of these policies. The research demonstrates that biofuel policies induce a shift toward greater diesel production at the expense of both gasoline and non-combustion petroleum products. This has the potential to result in an increase in greenhouse gas emissions, even before accounting for the emissions from producing the biofuels themselves.

The Food and Agriculture Organization of the United Nations suggest that out of all food that is produced, 1/3 ends up as food waste. In high income countries, such as Sweden, the food waste mainly originates from the last stages of the food chain, e.g. at food stores and households. Sweden is a member of the EU as well as the United Nations, and follows the common legislation for waste in the EU and has adopted the Sustainable Development Goals from the United Nations. In the Sustainable Development Goal number 12, food waste in terms of reduction is addressed, although Sweden does not have a clear goal that addresses how to reduce food waste. Food banks have globally been a strategy to redistribute surplus food from the retail sector to people in need, something that has not been common in the Nordic region of Europe (including Sweden) until the 1980’s. However, in Sweden, food banks have not been used as a way to prevent food waste but as a way to help people in need, perhaps because there is a well-established well-fare system in the country. Recently, initiatives that redistribute surplus food from the retail sector have been developed - working towards different consumer groups and solutions. This study aimed to map out the different surplus food redistributing initiatives in Sweden, categorise them and analyse some of the initiatives that represented different solutions and consumer groups. The chosen initiatives were ReFood, City Mission Uppsala (Matkassen and Mikaelsgården), City Mission Stockholm (Matmissionen), Food2change, Foodloopz and Allwin. The methods used for analysing the chosen initiatives were Environmental Life Cycle Assessment, Social Life Cycle Assessment and Life Cycle Costing. To weigh the environmental-, social- and economic impacts against each other, a total sustainability ranking system was used to point out the most favourable option for a redistributing surplus food initiative, in terms of sustainability. The results showed that the environmental impacts (Green House Gases (kg CO2 equivalents/functional unit)) were the lowest for, in this order, ReFood, Mikaelsgården and Allwin, Foodloopz, Matmissionen and Matkassen, and Food2change. For the social impacts, the results showed that Allwin is the initiative that redistribute the largest amount of surplus food to the consumer group “exposed people”, followed by Matmissionen that redistribute the second largest amount of surplus food to “people with low income”. Allwin is also the initiative with the highest capacity and largest yearly environmental savings, as the company redistributes a much larger amount of food than the other initiatives. The results for the economic impacts showed that all but one initiative, Food2change, have monthly financial losses. The overall sustainability ranking showed that the initiative that is the most favourable is Matkassen followed by Matmissionen and Allwin, Food2change, Foodloopz, ReFood and Mikaelsgården.

The building and construction sectors are one of the main contributors to the socio-economic development of a country. Globally, these sectors generate around 5% to 10% of national employment and around 5% to 15% of a country's gross domestic product during construction, use and demolition. On the other hand, the sectors consume around 40% of world primary energy, use 30% of raw materials, generate 25% of solid waste, consume 25% of water, and use 12% of land. Furthermore, the sectors account for up to 40% of greenhouse gas (GHG) emissions, mainly from energy use during the life cycle of buildings. This study aims to assess the potential environmental benefits of reusing concrete and ceramic roof tile within the Swedish context in terms of their CO2 emission. Methodology used was a comparative LCA was to quantify the emissions. In order to calculate LCA, OpenLCA 1.7.0 software was used and to evaluate the emissions, LCIA method selected was ReCiPe, midpoint, Hierarchist model, climate change category expressed in GWP 100 years (in kg CO2eq). The FU of the study was a square meter of roof covering for a period of 40 years with potential to extent up to 80 years. A square meter of concrete roof tile weight 40 kg while ceramic 30 kg. The environment impact evaluation considered three product system, single use (cradle to grave), single use covering (cradle to user) and single reuse (user to cradle) within 40 years lifespan. In order to compare LCA of the roof tiles, two scenarios were created, Scenario 1 concrete RT in single use and single reuse whilst Scenario 2 evaluates ceramic RT. The outcomes of both scenarios were communicated through a model single family house. Dalarna’s Villa is located in Dalarna region in Sweden and a storage facility Ta Till Våra was to validate the benefits of reused materials. Comparative LCA revealed that concrete RT in single use released almost 80% more CO2 emissions than ceramic RT and generated 25% more disposable material by weight. The CO2 released by the single use vs. single reuse concrete RT showed higher emissions in the production of the concrete RT than the single reuse, the same occur with ceramic RT. The reuse of the tiles on the same site had an insignificant impact on the environment in both materials. The comparison shows that reuse reduces associated emissions by about 80% in both cases, reusing concrete is more beneficial, as emissions are reduced by 9.95 kg/m2 as opposed to 2.32 kg/m2 at the ceramics. This study reveals the benefit of reusing concrete and ceramic roof tile. In addition, the advantage of building a storage facility to reuse the disposable building materials, reducing the roofing materials ending at the landfill after 40 years. Furthermore, it demonstrated the reduction of CO2 emissions associated with the embodied energy.

A presente se tese desenvolve uma metodologia para comparar as substâncias emitidas na construção e operação de sistema frigorífico por absorção e por compressão de vapor de amônia usando a metodologia denominada Análise do Ciclo de Vida (ACV). Pesquisas bibliográficas feitas pelo autor desse trabalho permitem a conclusão de haver poucas informações que permitam a elaboração de um inventário de ciclo de vida para ciclo frigorífico por absorção e por compressão de vapor tendo como fluido de trabalho a amônia. Realizado todo o dimensionamento termodinâmico e mecânico dos ciclos e aplicada a metodologia ACV, os resultados demonstram que a operação do ciclo frigorífico por compressão produz 626,91% mais de hidrocarbonetos quando comparada com a quantidade emitida devido a construção. Demonstram ainda que as substâncias emitidas são diferentes para o ciclo por absorção e para o por compressão de vapor de amônia. / This thesis proposes to develop a way to compare the substances emitted in the construction and operation of a refrigeration cycle by absorption and compression of vapor ammonia using the methodology called Life Cycle Analysis (ACV). Bibliographic researches made by the author of this study suggest there is little information to allow the construction of an inventory of the life cycle to a refrigeration systems. Carried out all the thermodynamic and mechanical design cycles and applied the ACV methodology, the results demonstrate that the operation of the compression cycle produce 626,91% more hydrocarbon in comparison with the construction. The results shows that the substances emitted by absorption or compression cycle are different.

Global plastic pollution of the natural environment is extremely detrimental as it is causing deaths of animal species. More than 80 % of marine litter is made up by plastics and 70 % of those are made up by disposable items. For this reason, the European Parliament has agreed to abolish the top ten single-use plastic items found in the marine environment from the EU market from 2021. Therefore, the fossil-based disposables will need to be substituted by disposables made from renewable materials. It is thus important to investigate the environmental impact of these alternatives through their life cycle in order to support sustainable consumption and production. In this study, environmental impact of disposable plates made from two different renewable materials (paper and leaf) were analysed by means of life cycle assessment (LCA). The aim of the study was to examine the environmental performance of the two plates in the impact category global warming potential (GWP); and reveal the processes with the largest contributions to the overall GWP of each plate. The leaf plate was produced in India and the paper plate in the Nordics, however, both plates were used and disposed of in Uppsala, Sweden. The results showed that the leaf plate has a higher GWP due to its long-distance transport and electricity use derived from fossil fuels. Scenario analysis has proved that its GWP can be reduced when sea transport route is chosen instead of flying and production is increased. When it comes to the paper plate life cycle, the processing stage was identified to contribute the most to the total GWP. It could be further improved by applying a biodegradable layer for its coating. To keep the good performance in GWP the plate should be incinerated with energy recovery. The disposal of the plates has a substantial positive influence on their total carbon footprint as both plates substitute use of fossil fuels. However, the credits allocated for the different waste management options are specific to Uppsala and thus the results of this study should be applied only under similar conditions.

A noção de que o consumo de produtos manufaturados atinge adversamente o suprimento de recursos e a qualidade do meio ambiente fez com que o mercado consumidor exigisse das corporações e dos organismos reguladores medidas mais eficientes quanto a preservação da Natureza. Através de iniciativas como essa renasceu um instrumento de gestão ambiental conhecido por Análise de Ciclo de Vida - ACV. A ACV é uma metodologia criada para identificar aspectos ambientais e quantificar seus impactos associados, ao longo de todo seu ciclo de vida, ou seja, desde a extração de matérias-primas, até a disposição final do produto, novamente no meio natural. Seu uso auxilia na priorização de ações de melhoria visando a prevenção da poluição,permitindo uma alocação mais adequada de recursos materiais, humanos e econômicos. Além disso, estimulariam o aumento da competência e favoreceriam a inovação tecnológica, considerando sempre a relação custo-benefício envolvida. O objetivo desse trabalho é propor um modelo de ACV que seja adaptado às condições brasileiras. Para a comprovação do modelo, foi estudado o caso de produção de um fertilizante fosfatado - superfosfato simples. Verificou-se que por ser a ACV uma metodologia amplamente dependente de dados precisos e confiáveis, a indisponibilidade de bancos de dados genuinamente nacionais limita em muito seu raio de aplicação no país. Entretanto, foi possível constatar também, que mesmo diante dessa limitação,o uso da ACV amplamente aplicável na prática, principalmente no que se refere a hierarquização de ações de melhoria de desempenho ambiental de um produto. Verificou-se ainda que o ciclo de vida de manufatura do superfosfato simples não traz impactos significativos sobre o meio ambiente. Suas maiores contribuições em termos de impactos ambientes são relativas ao Aquecimento Global - dada a predominância de transporte rodoviário np país - a Eutrofização - em função das constantes ) perdas de processo - e a redução do espaço físico, motivada pela elevada geração de resíduos sólidos por ocasião da etapa de beneficiamento da rocha fosfática. / The society is actually convinced that the manufactured products bring problems to the Nature mainly, in terms of resource depletion and environment quality. This posture make the government and the corporations change their ways to deal with environmental management. In this picture, appeared again the life cycle assessment. LCA is a tool used to identify environmental damage, and evaluate it\'s proportion. From the cradle to grave of a product. Besides, LCA can support improvement actions, in the way of the pollution prevention, permitting tha allocation of material, human and economic resources. The goal of this scientific work is to propose a model of life cycle assessment specific to the brasilian condition. To test the model it was studied the manufacturing life cycle from the single superphosphate. The main conclusion\'s were that, even with deep limitation in term of databases extricate from Brazil, limited the use of the methodology to qualitative conclusions. On the other side, the model, even needing some sets, proved being useful in practical studies. In term of superphosphate, the most significative environmental impacts are Global Warming, because of the material transportation in Brazil is basically by road do the Nitrification, because the losses of the process. In general, the single superphosphate has, in reality low environmental profile.

A sustentabilidade do planeta é responsabilidade coletiva e ações para melhorar o ambiente global são necessárias e implicam na adoção de práticas de produção e consumo sustentáveis. O desenvolvimento da Indústria Têxtil e Confecção incorpora tecnologias nos campos das ciências físicas, químicas e biológicas necessárias às atividades do setor, desde a obtenção da matéria-prima, produção de fios e tecidos e, seus respectivos acabamentos, consumindo grandes quantidades de recursos e energia. O Desenvolvimento Sustentável ao expandir o foco econômico para as dimensões ambiental e social dos processos de produção e serviços originou uma visão sistêmica dos inputs e outputs do processo produtivo e suas consequências ambientais, estruturando o conceito de ciclo de vida do produto (ACV). O objetivo desse estudo é avaliar o ciclo de vida de uma calça feminina confeccionada em malha de poliamida, utilizada como uniforme do ensino médio estadual no Paraná, do berço ao túmulo, com 3 possibilidades de descarte. Foi realizado um estudo de caso para verificar a viabilidade de aplicação da ferramenta ACV para avaliação do impacto ambiental do produto final por meio do software LCA SimaPro8.1.16Faculty. A coleta de dados foi realizada por meio de questionário, baseado nas diretrizes da NBR ISO 14040 que determinam as fases e procedimentos gerais da execução de um estudo de ACV, para identificar a estrutura produtiva da empresa de confecção permitindo o levantamento quantitativo de dados referentes ao processo produtivo, a identificação das entradas e saídas de materiais e energia elétrica e, a quantificação dos resíduos gerados. Algumas informações foram retiradas do banco de dados de inventários de processos disponíveis no software utilizado para este estudo. A avaliação do ciclo de vida da calça de poliamida foi baseada no Manual do Sistema Internacional de Referência de Dados sobre o ciclo de vida de produtos e processos (ILCD). A tabulação dos dados do produto foi realizada no software SimaPro8.1.16Faculty. A base de dados de inventário selecionada foi a Ecoinvent v.2 e, para realização da análise de impacto foi adotado o método de impacto gerado Eco-indicator 99. O software LCA SimaPro 8.1.16 Faculty mostrou-se ferramenta eficiente para a realização da avaliação do ciclo de vida da calça de poliamida com os três cenários de descarte, permitindo a análise dos impactos ao nível da categoria de danos para a saúde humana, qualidade do ecossistema e recursos e, possibilitando a análise da carga ambiental por categoria de impacto, de acordo com o que propõe a ISO 14042 sobre os elementos de seleção de definição de categorias para a fase de Avaliação / The sustainability of the planet is collective responsibility and actions to improve the global environment are necessary and imply the adoption of sustainable production and consumption practices. Development of Textile and Confection incorporates technologies in the fields of physical, chemical and biological sciences necessary to the sector\'s activities, from obtaining the raw material, production of yarn and fabric and their finishes, consuming large amounts of resources and energy . Sustainable Development to expand economic focus to environmental and social dimensions of production processes and services led to a systemic view of the inputs and outputs of the production process and its environmental consequences, structuring the concept of product life cycle (LCA). The aim of this study is to evaluate the life cycle of a woman\'s pants made of polyamide fabric, used as a uniform average state school in Parana, from cradle to grave, with 3 possibilities for disposal. A case study was performed to verify the application feasibility of LCA tool for assessing the environmental impact of the final product through ACL SimaPro 8.1.16 Faculty software. Data collection was conducted through a questionnaire, based on the guidelines of ISO 14040 which determine the general phases and procedures of the execution of an LCA study, to identify the productive structure of the clothing firm allowing the quantitative survey data for the production process, the identification of the inputs and outputs of materials and energy, and the quantification of waste generated. Some information was taken from the inventory database processes available in the software used for this study. The evaluation of the polyamide trousers life cycle was based on the International System Manual Data Reference on the lifecycle of products and processes (ILCD). Tabulation of the product data was performed in SimaPro8.1.16Faculty software. The selected inventory database was Ecoinvent v.2 and to perform impact analysis was adopted impact generated method Eco-indicator 99. The LCA SimaPro 8.1.16 Faculty software was efficient tool for the realization of assessment of the life cycle of the polyamide pants with three disposal scenarios, allowing the analysis of impacts on the category of damage to human health, ecosystem quality and resources, enabling the analysis of environmental load by impact category, according to which it proposed to ISO 14042 on the selection of elements to define categories for the phase evaluation

Este trabalho desenvolve um método de seleção de fronteiras para Análise de Ciclo de Vida (ACV) de sistemas que emitem componentes tóxicos. Isto envolve o desenvolvimento de um modelo de predição de concentração e dose de poluentes emitidos de chaminés, que tem a vantagem de ser simples e não requerer grande número de dados de entrada. Esse modelo e mais os dados de valoração econômica de danos ambientais disponíveis na literatura, compõem o modelo geral de estimativa de custos devido à emissão de poluentes, ou seja, a Análise de Custos em Ciclo de Vida (ACCV). O modelo geral é então usado para definir as fronteiras do sistema de ACCV. Demonstra-se a aplicação do novo método em um ciclo de vida hipotético de produção de celulose. / This work develops a method for Boundary Selection (BS) for Life Cycle Assessment (LCA) of systems with stacks emitting toxics compounds. The new approach involves the development of a model of concentrations and dosage of pollutants in the vicinity of emission source that is simple and non-intensive data is required. This model plus impact costs estimations available at environmental economic studies, comprise the general model of Life Cycle Cost Analysis (LCCA) based on exposure. This general model is then used in the Boundary Selection in LCCA. A demonstration of the application of the model is performed to a hypothetical inventory system of a pulp mill.

O presente estudo apresenta a construção de uma ferramenta para avaliação do ciclo de vida - ACV das edificações durante a fase de construção. A princípio, é realizada uma vasta pesquisa, visando à contextualização do tema, por meio da elaboração do estado da arte da ACV na construção civil, que abrange estudos diversos (nacionais e internacionais), focados na pesquisa do consumo de energia - Eprim e fator de emissão de CO2 - FE. Posteriormente, parte-se para a elaboração dos métodos, que envolve a definição dos principais insumos materiais, cálculo de consumo de Eprim e FE dos insumos energéticos e materiais, e dos equipamentos usados durante a fase de obra. O método contempla a descrição da construção da ferramenta propriamente dita. Nesta etapa, observa-se que há uma variação considerável nos valores de Eprim e FE para um mesmo insumo material, como por exemplo, a madeira usada na obra, cujo consumo de energia primária variou entre 5 GJ e 48 GJ, e seu fator de emissão entre 0,07 kgCO2/t e 4.199 kgCO2/t, isso porque há diferenças entre os estudos analisados, que envolvem a matriz energética do país de origem do material, seu processo produtivo e o escopo adotado pelo autor. O trabalho apresenta os principais materiais da obra em termos de massa, e também a representatividade deles em relação ao consumo de energia primária e a emissão de CO2, assim o concreto isoladamente representa no edifício, 61% de massa, 68% do consumo de energia primária e 60% das emissões de CO2. A análise do uso do edifício por meio de dados genéricos de consumo de eletricidade, de gás natural e de água/esgoto, indica que a maior representatividade em termos de consumo de energia primária, se dá pela eletricidade com quase 85%, enquanto a emissão de CO2 representada pelo gás natural é de 43%. Já nas etapas de construção, 93% do consumo total de energia primária estão associadas aos insumos materiais, e esta fase representa 81% do total das emissões de CO2. / This study presents the construction of a life cycle assessment - LCA tool of buildings, with spetial focus on the construction phase. Initial an extensive research is carried out in order to contextualise the issue, through the development of state of the art of LCA in construction, covering several studies (national and international), research focused on primary energy consumption - Eprim and CO2 emission factor - EF. Later, we proceed to the elaboration of methods, involving the definition of key material inputs, calculations of Eprim and FE of materials and energy inputs, and equipment used during the construction phase. The method includes the description of the tool construction itself. In this step, it is observed that there is considerable variation among the values of Eprim and EF for the same input material, such as wood used in the work, whose primary energy consumption varied between 5 GJ and 48 GJ, and its factor emission between 0.07 kgCO2/t and 4.199 kg CO2/ t, this is because there are differences between the analyzed studies involving the energy matrix of the country of origin of the material, its production process, and the scope adopted by the author. The master thesis indentifies the main material in terms of mass, and also the representativeness of the materials in relation to primary energy consumption and CO2 emissions. Concrete represents 61% by weight, 68% of primary energy consumption and 60% of CO2 emissions. The analysis of the use phase of the building through generic consumption data of electricity, natural gas and water / sewer, indicates that utilities are important in terms of primary energy consumption, electricity is almost 85%, while the CO2 emission represented by the natural gas is 43%. Already in the construction stages, 93% of the consumption of primary energy are associated with material inputs, this phase represents 81% of total CO2 emissions.

Recentemente, a sociedade tem empreendido ações visando minimizar os impactos ambientais associados ao atendimento de suas necessidades. A reciclagem é uma atividade de destaque e que pode contribuir para que este novo objetivo seja atingido. Porém, as eventuais vantagens decorrentes da reciclagem devem ser analisadas de forma quantificada e sistêmica, ou seja, através de estudos de Avaliação do Ciclo de Vida (ACV) dos produtos. Por outro lado, o método de execução de estudos de ACV apresenta aspectos não consolidados. Um exemplo, é a modelagem de sistemas de produto que envolvam o reaproveitamento de rejeitos, para a qual não há consenso na comunidade científica a respeito da abordagem mais adequada. Neste contexto, esta pesquisa visa a consolidação das alternativas para a abordagem do reaproveitamento de rejeitos em estudos de ACV. Os modelos identificados variam, basicamente, segundo três abordagens. Uma delas é baseada na expansão do sistema, com o objetivo de se evitar a necessidade de alocação de cargas ambientais. Esta abordagem tem a vantagem de considerar diretamente os eventuais benefícios decorrentes do reaproveitamento dos resíduos. Já a segunda abordagem baseia-se na alocação das cargas ambientais associadas aos processos de obtenção das matérias-primas e/ou ao reaproveitamento em si, bem como a disposição final dos rejeitos entre os Sistemas de Produto envolvidos. Por fim, a última abordagem prega a atribuição das cargas ambientais associadas aos processos citados anteriormente exclusivamente à função atendida por cada sistema. Assim, o sistema que fornece um produto pós-consumo para o reaproveitamento arca com as cargas decorrentes da obtenção das matérias-primas, enquanto o sistema que reaproveita o produto pós-consumo fica responsável pelas cargas associadas à reciclagem em si, bem como à eventual disposição final. Salienta-se que este tipo de modelagem privilegia as situações em que um determinado sistema de produto utiliza insumos reciclados, uma vez que estes entram no sistema livres de carga ambiental pregressa. / Recently, human society has taken actions in order to minimize the environmental impacts associated with meeting their needs. Recycling is an important activity that can contribute to the achievement of this new goal. However, the possible benefits of recycling should be considered systemically, i.e., through Life Cycle Assessment (LCA) of products. On the other hand, LCA method implementation has some unconsolidated aspects. One example is the modeling of product systems end-of-life involving waste recycling, for which there is no consensus in the scientific community regarding the most appropriate approach. In this context, this research aims to consolidate the alternative approaches for modeling wastes recycling in LCA studies. The identified models vary primarily according to three approaches. One of them is based on product system expansion in order to avoid the need for environmental burdens allocation. This approach has the advantage of directly considering the possible benefits of reusing waste. The second approach is based on the allocation of environmental burdens associated with raw materials processing, recycling and final waste disposal between product systems involved. Finally, the last approach considers the attribution of environmental burdens associated with the mentioned processes exclusively the function served by each system. Thus, the system providing a post-consumer product for reuse bears the burdens arising from raw materials processing, while the system that recoveries the post-consumer product is responsible for the loads associated with the recycling as well as eventual final waste disposition. It is noted that this modeling approach favors situations in which a particular system uses a recycled product as raw material, since they enter the product system free of previous environmental burdens.