End-of-life Tires Research Articles

Modeling the Socioeconomic Metabolism of End-of-Life Tires Using Structural Equations: A Brazilian Case Study

Socioeconomic metabolism (SEM) is the exchange of materials and energy between society and the environment involving the social, economic and environmental sectors. In this paper, a boundary was defined between the economic (consumption) and environmental (waste recovery) limits in a city of 300,000 inhabitants in relation to the circulation (generation, reuse and disposal) of end-of-life tires (ELTs). The objective was to elaborate a theoretical structural model to evaluate the socioeconomic metabolism of waste (SEMw) by means of technical constructs (direct material flows (DMF), reverse material flows (RMF), socioeconomic environment (SEF) and sociodemographic factors (SDF)). Structural Equation Modeling (SEMm) was performed using Partial Least Squares Structural Equation Modeling (SmartPLS) software. The results obtained from the hypotheses show the causal relationships between the technical and social constructs and suggest guidelines for supporting the planning and management of urban solid waste in the collection and final disposal of ELTs. The processed information also contributes to the analysis of the city’s socioeconomic scenarios in relation to the disposal of ELTs. One of the hypotheses tested (RMF have a direct effect on SEMw) shows the importance of managing ELTs through the correct final disposal of waste and recycling. SEMw was evaluated from the perception of the local society and it is concluded that it is possible to plan public policies to avoid the formation of waste inventory in the city.

ERASSTRI - European risk assessment study on synthetic turf rubber infill – Part 3: Exposure and risk characterisation

As the final part of a Europe-wide study on the risk from synthetic turf infill consisting of rubber granules derived from end-of-life tyres (ELT), exposure of sportspeople was assessed and compared with health-based reference values for various chemical substances. Based on information from previous project phases, exposure scenarios were established and exposure was calculated for oral, dermal and inhalation routes. Calculated cancer risks for exposure to polycyclic aromatic hydrocarbons were below 1:1 million. Risk characterisation ratios (RCRs) for non-carcinogenic substances were below 1, indicating no health concerns. For 2-hydroxybenzothiazole no toxicological data were found from which to derive a substance-specific reference value. A threshold-of-toxicological concern approach revealed maximum RCRs slightly above 1, which are acceptable, given the conservativism of the approach. ERASSTRI substantially improved the data available for assessing human health risks from using ELT-derived infill material. Overall, no health concerns could be identified for the use of synthetic turfs with ELT-derived infill material.

The influence of preliminary processing of end-of-life tires on transportation cost and vehicle exhausts emissions

Recovery and recycling end-of-life tires (ELT) incur a significant cost of collection and transportation. Improperly conducted ELT collection contributes to excessive vehicle exhaust emissions and high transportation costs. This study investigates the collection and transportation costs of ELT including preliminary processing of waste tires like cutting, baling and packing tires to reduce the volume of each shipment. Waste collection vehicles exhaust emissions were examined in the collection scenarios. In this study a novel approach of multi-criteria decision support - coupled analytical hierarchy process (AHP) and Preference Ranking Organization METHod for Enrichment of Evaluations (PROMETHEE) methods have been applied for selecting the best scenario, considering costs and environmental impacts in the collection of ELT. The results show the most profitable method of the ELT collection by routing of heavy truck and pickup of waste tires from a local network after preprocessing. Packing the tires in the collection points reduces the total cost between 20-30% and vehicles' exhaust emissions up to 40 %, compared to other methods in the Polish case study. The proposed decision support method is useful for evaluating environmental and cost factors, especially in regions where transport costs due to distances constitute the largest share of costs. This method and the results are useful for the ELT collection companies in promoting sustainable methods of transportation of waste including emission and economic factors. The study encourages using the compacting of ELT at the collection points for more efficient transportation.

Technology comparison for the production of fine rubber powder from end of life tyres

The present paper addresses grinding technologies for the production of rubber powder from end of life tyres (ELT) in industrial scale. Cryogenic grinding was compared with different ambient grinding processes using the same feedstock (truck or passenger car). Processing capacity, energy requirement, particle size distribution and morphology were determined. In addition, the influence of the underlying grinding process on the particle properties and those of the vulcanizates produced therewith are addressed.

Implementation of circular economy principles in management of end-of-life tyres in a developing country (Nigeria)

Linear economy principles still dominates production and consumption model across the globe. However, the pursuit and implementation of circular economy model is growing. This model shift is sustained by the global movement towards the concept of sustainable development. Nigeria, a developing country has a very poor waste management system. This paper review discussed challenges and opportunities offered by post-consumer management of end-of-life tyres in Nigeria. End-of-life tyres (ELTs) cause a multi-faceted problem in Nigeria. They are issues with human health (abattoirs, breeding ground for mosquitoes, emissions, etc) and issues with the environment (linear economy, unrecovered resource, air pollution and contaminated land from abattoirs). These two factors form the underlying challenge which the paper addressed. Currently, the management of ELTs in Nigeria has serious negative ecological implications. It takes more than a century for a tyre to biodegrade, occupies much space in dumpsite, is highly flammable, and is generated annually in large volume. The use of tyre in roasting of meat is a common practice in abattoirs across Nigeria. It has led to elevated levels of heavy metals in meat. Therefore, the need for a sustainable approach. Socioeconomic limitations, scarcity of progressive environmental policy, technical and institutional incapacity have severely limited implementation of proper waste management system which is critical for operationalized circular economy. The paper also discussed potential directions on the application of CE model in ELT management, including policy and legislation. Factors unique to Nigeria supports the proposed integration of extended producer responsibility (EPR) and the free market system as the appropriate circular management approach of end-of-life tyres for the country. The study recommends formation of a producer responsibility organization nationally. However, for effective logistics, regionalization of the collection / processing facilities will foster competition and drive innovation in the post- consumer tyre management.

Assessment of heavy metals in simulated leachates and the ashes of end-of-life tyres

Tyres are rubber-based materials with a complex structure. This study assesses the levels of heavy metals in simulated leachate of end-of-life tyres (EoLT) and its ashes. Two passenger car and motorbike tyres and their ashes were subjected to TCLP, SPLP and DIN Batch test to simulate their environmental impacts. Heavy metals in the simulated leachates and ashes were determined using Atomic Absorption Spectrophotometer (AAS) after acid digestion of the samples. Heavy metals concentrations varied with the types and quality of the tyres. Zinc concentrations was the highest among the heavy metals determined. The concentrations of heavy metals in the TCLP leachates of EoLT ranged from 0.02-0.06 mg/L Cu, 3.13-5.86 mg/L Zn, 0.004-0.03 mg/L Cd, Not detected (ND)-0.04 mg/L Cr, and 0.08-0.13 mg/L Pb. This showed that EoLT are potential source of heavy metals loading in the environment. Thus, the need for their appropriate management is imperative.

Upgrading pyrolytic carbon-blacks (CBp) from end-of-life tires: Characteristics and modification methodologies

Over 1 billion end-of-life tires (ELTs) are generating annually, and 4 billion ELTs are currently abandoned in landfills and stockpiles worldwide, according to the statistics, leading to the environmental and health risks. To circumvent these issues, pyrolysis, as an attractive thermochemical process, has been addressed to tackle the ELTs’ problem to reduce the risks as well as increase the material recycling. However, due to the lack of systematic characteristic analysis and modification methods, poor quality of CBp limits the improvement of ELTs pyrolysis in industry applications, which plays a crucial role in the economic feasibility of pyrolysis process. In this review, we have summarized the state-of-the-art characteristics and modification methodologies of the upgrading of CBp, to in-depth understand the surface microstructures and physiochemical properties of CBp for the foundation for modification afterwards. By virtue of the proper selection of modification methods and modifying agents, the new generation of multifunctional carbon materials with desired properties can be instead of the traditional materials of CB, promising broader and various application fields.

Comparative life cycle assessment of standard, cellulose-reinforced and end of life tires fiber-reinforced hot mix asphalt mixtures

A change in the current waste management practices is needed to improve the reuse and recycling rates and limit the increasing environmental impacts (EI) on the environment. The construction sector is one of the major contributors to the global EI, regarding energy consumption, emissions released into the atmosphere and extracted natural resources. In this context, the reuse of waste and scraps from other sectors/production chains (i.e. fibers from end of life tires – ELT) in road pavements potentially represents a best practice.This study presents a comparative life cycle assessment (LCA) among three different typologies of hot mix asphalt mixtures (HMA): standard, cellulose-reinforced and ELT fiber-reinforced. The study focuses on the environmental analysis of the realization and maintenance of 1 m2 of HMA mixtures for a motorway road, during a time lapse of 30 years. The life cycle inventory includes primary data, collected from different industrial companies and from laboratory test, secondary data, derived from the GaBi professional database 2016. The service lives of the different typologies of HMA have been evaluated through a laboratory study and a full-scale application in a trial section located in an important Italian motorway. The porous asphalt mixture containing ELT fibers showed about 70% increase in the fatigue resistance with respect to the porous asphalt mixture containing cellulose fibers. The environmental impacts have been quantified in terms of Cumulative Energy Demand (CED), Global Warming Potential (GWP), and ReCiPe midpoint and endpoint indicators.The obtained results show that raw materials (particularly bitumen) are the most impactful flows for all the three considered mixtures and for all the impact categories. Also the transportation phases contribute with relevant impacts, while energy flows consumed during the HMA preparation and laying are almost negligible. Considering the CED, GWP and ReCiPe endpoint indicators, the ELT fiber-reinforced HMA resulted the best alternative (reduction of 25% in comparison with the standard HMA), followed by the cellulose-reinforced HMA (−10%), thanks to the higher service life. For some ReCiPe midpoint categories (Agricultural land occupation, Freshwater ecotoxicity, Freshwater eutrophication, Marine eutrophication and Terrestrial ecotoxicity), instead, the worst scenario is the cellulose HMA, due to the high contribution of the cellulose material.

Sustainable reuse of Waste Tire Textile Fibers (WTTFs) as reinforcement materials for expansive soils: With a special focus on landfill liners/covers

Abstract As a sub-product in the treatment process of End of Life Tires (ELTs), Waste Tire Textile Fibers (WTTFs) are hazardous waste materials that are traditionally buried or burned as opposed to the international laws. Due to the soaring demand for tires and vehicles, disposing of WTTFs imposes a heavy burden on the environment mainly because of two reasons: i) they occupy massive valuable space in landfills, and ii) burning them leads to dangerous gas emission. In this research, the feasibility of reusing WTTFs as reinforcement agents in an expansive soil was investigated through a comprehensive set of laboratory experiments, i.e. standard compaction, Split Tensile Strength (STS), swelling-consolidation, volumetric shrinkage, and desiccation cracking tests. According to the results, WTTFs can enhance all of the investigated geotechnical characteristics of the expansive soil. Moreover, it was proven that WTTF-expansive soil mixtures can be used as a suitable material for impermeable liners and covers in landfills. Therefore, instead of burying or burning them, WTTFs can be competently employed as reinforcement materials in expansive soils.

Methods of the end-use of end-of-life tires

The main objective of the study, presented in the article, is to review the possible methods of final recovery of End-of-Life Tires (EOLT). Applied methods of the end-use of EOLT used in Republic of Bulgaria and in some other countries in the European Union are presented and commented in the paper. Also the end-use of EOLT waste criteria is discussed. The possibilities for post-recovery including recycling of the waste generated by the tire recovery process have been explored. The application of the identified methods in Republic of Bulgaria and other European Union Member States have been analyzed and assessed.

Novel biofuels derived from waste tyres and their effects on reducing oxides of nitrogen and particulate matter emissions

Abstract There are tons of waste tyres produced each year globally. Production of oil from the waste tyre not only manages the wastes but also produces fuels for compression ignition engines. In this investigation, a novel approach developed by Green Distillation Technologies in Australia was used to convert whole end of life tyres (ELTs) into carbon, steel, and tyre oil. The physicochemical properties of the tyre oil are similar to diesel fuel, and the fuel is miscible with diesel in any blended ratio. An engine experiment was conducted on a EURO IIIA diesel engine. All experiments were performed at constant speed and four different engine loads. Two blends (10% and 20%) of tyre oil were compared to reference diesel fuel. Exhaust emissions, including gaseous emissions, particulate matter (PM) and particulate number (PN) were investigated. The results indicate simultaneous reductions in both diesel PM and nitrogen oxides (NOx) emissions with the tyre oil blends when compared to diesel. NOx emissions were reduced by approximately 30% with both blends with respect to diesel. The reduction in PM and PN emissions were in the range of 35–60% and 5–20%, respectively. Carbon monoxide (CO) were increased by ∼ 10% compared to the reference diesel except at quarter load. Insignificant change in brake power (BP), brake mean effective pressure (BMEP) and brake thermal efficiency (BTE) were observe with the tyre oil blends. The engine remained compliant with its EURO IIIA guidelines during the use of the tyre oil blends. Based on the engine performance and emission result, the tyre oil could be alternative to traditional diesel fuel.

INFLUENCIA DE LA INCORPORACIÓN DE FIBRAS DE CAUCHO PROCEDENTE DE NEUMÁTICOS FUERA DE USO (NFU) EN MORTEROS DE YESO. ESTUDIO DE LAS PROPIEDADES MECÁNICAS, TÉRMICAS Y ACÚSTICAS

In this paper, results about an experimental study performed on plaster compounds with the incorporation of rubber in the form of fibers from end of life tires are reported and analyzed. Test samples of plaster are prepared adding different volumetric fractions of rubber fibers that had been previously classified into two different sizes. The same consistency is fixed for every compound studied. Physical and mechanical properties are analyzed. Thermal behavior is also studied comparing thermal conductivity values and relating them with the bulk density of the resulting material. The results show an improvement in the thermal behavior proportional to the reduction of the density and the mechanical properties, as the proportion of rubber increases. It is also observed that there are no significant differences depending on the size of the fibers. These results confirm that the new material obtained is comparable to other materials of lightweight plaster with improved thermal properties and therefore with the same possibilities of use as these materials. The new material could be used for slabs and compression layers in building rehabilitation. Keywords: Plaster, rubber fibers, mechanical properties, thermal conductivity, acoustic insulation.

End of Life Tires as a Possible Source of Toxic Substances Emission in the Process of Combustion

Several million tons of end of life tires (ELTs) are piled annually as a result of human activities. Various methods have been proposed for the extraction and recycling of the resource potential of ELTs. The chemical composition of ELTs seems to enable their usage as a fuel after mechanical separation of a steel cord. Indeed, in the rubber of ELTs, up to 90 mass% accounts for carbon and hydrogen. Currently, it is by incineration that a significant proportion of ELTs is utilized. However, ELTs contain not only sulfur, which is used for vulcanization, but also nitrogen-containing additives. The behavior of these heteroatoms during oxidation is poorly investigated. It has been shown that the pyrolysis liquid fuel obtained from ELTs contains such sulfur compounds as mercaptans and nitrogen in the form of hydrocyanic acid and cyanogen. Deep oxidation of ELTs results in the oxidation of sulfur compounds to dioxide, but the oxidation products have been found to contain traces of cyanogen. Taking this into account, one should pay attention to the ways of transforming heteroatoms during the process of ELT oxidation and the products of ELT pyrolysis as potential sources of highly toxic gas emissions.

Study on the Thermal Decomposition of Plastic Residues

The use of plastics in the last decades significantly increased, thus plastic recycling processes are needed. Generally, mixtures of plastic materials are disposed together, hence the recovery of the polymeric material is difficult and expensive. Plastic residues could be valorized by thermal degradation processes aimed at recovering energy and/or valuable compounds for chemical industry. The main technologies used for this purpose are gasification and pyrolysis. The latter is a thermal degradation process that occurs in the absence of oxygen at moderate temperature (300-700°C), that could be used to recover the thermal power of biomasses. The reaction products are bio-oil, biogas and biochar. The aim of this work was to employ pyrolysis to energetically exploit different pure plastic materials, namely polyethylene terephthalate (PET), polyamide (Nylon-6), polyvinyl chloride (PVC) and polyurethane (PU), as well as a complex one such as end of life tyres (ELT). The reaction was performed at 400 °C for 90 min. The pyrolysis system was composed by a tubular quartz reactor heated with a tubular vertical oven. An integrated condenser was used to separate the liquid reaction products, while the incondensable gases were collected in a latex balloon. The reaction products were quantified gravimetrically and, in order to evaluate the functional groups, characterized by FTIR analysis. The reaction gases were also analyzed by GC-MS to determine the composition of this fraction. Results obtained from the different plastics were significantly different in terms of distribution and composition. In particular, PET produced a biogas consisting mainly of acetaldehyde and hydrocarbons, while the liquid fraction was composed of benzoic and terephthalic acids. Nylon-6 degraded producing a large amount of reaction gas (65 g/100g) composed of ammonia and light hydrocarbons, while the reaction liquid was mainly caprolactam. Around 53 g/100g of PVC reaction products were gaseous, mainly hydrochloric acid, followed by toluene and benzene at high concentrations. The degradation of PU produced a reaction gas, mainly composed by formic and acetic aldehydes. ELT pyrolysis was responsible for the production of high amounts of solid residue, while reaction gas and liquid seemed to be mainly constituted by hydrocarbons. In general, the study of pure plastic pyrolysis could help to better understand the thermal decomposition of complex plastic residues such as ELT.

Improving the Environmental Sustainability of Low Noise Pavements: Comparative Life Cycle Assessment of Reclaimed Asphalt and Crumb Rubber Based Warm Mix Technologies

Increasing environmental awareness is pushing towards sustainable approaches to the design and management of transport infrastructures. A life cycle assessment of low noise pavements is carried out here, with the aim to evaluate and compare the use of warm mix asphalts containing crumb rubber (CR) from end-of-life tires (ELTs) and reclaimed asphalt pavement (RAP). Different scenarios have been considered, taking into account production, construction, maintenance activities, and end-of-life of the pavement, according to a cradle to grave approach. Hot mix asphalt (HMA) was used as a reference wearing course. Results show that the simultaneous implementation of warm asphalt technologies and recycled materials can lead to a 50% reduction of the environmental burdens, compared to the standard scenario. The difference is mainly ascribed to the material depletion, the energy consumption, and the emissions associated with the frequency of maintenance of the wearing course. The use of asphalt rubber is environmentally advantageous, if compared to polymer modified binders (PMB); moreover, rubberized open-graded mixtures require the lowest bitumen content and maintenance. The findings of this research support the use of recycled materials and warm technologies as a way to improve the environmental sustainability of low noise pavements.

Tire waste management system in Cyprus in the framework of circular economy strategy.

Worldwide, waste raised from tires counts 1.3-1.5 billion tonnes/year and by the end of 2025, is expected to be more than 2.5 billion tonnes. On 2013, the EU countries reached 3.6 million tonnes of used tires. However, the cheapest treatment method since now is landfilling and is considered to be a major threat for the environment and the public health. In Cyprus, the total tires that were imported on 2015 was 835,142 pieces (5.8% more than the 2014), which were equal to 9638 t, while at the same time, the total waste from those tires were 6629 tonnes. Moreover, the cement industry used 6691 tonnes of tires as alternative fuel. Until now, there are three management systems in place in Cyprus, for the end-of-life tires (ELTs). The collection of ELTs on 2011 was 1817 tonnes while at the end of 2016 was 7201 tonnes. The main treatment methods in Cyprus are the use of ELTs as alternative fuel in cement industry or to produce rubber granules (609-2738 tonnes/year) to be used to construct artificial surfaces or substrate for artificial lawn grounds and limited to pyrolysis (324-837 tonnes/year). At the same time, the environmental fees for the collection of tires varies and depends on the tire category. Furthermore, the market share of ELTs is up to 1.5 million € and the total recovery index from the market is closed to 90% the last 6 years (2013-2017). This paper evaluates and assess the existing tire waste management system (TWMS) in Cyprus in order to promote strength and weakness as well as to propose a holistic management system in insular communities in order to adopt the targets set by the concept of circular economy. The SWOT analysis identified as the main weaknesses the absence from the legislation of specific target for the recovery index of tires and the absence of any centralized logistic system to control the existing management systems while the main threats includes bureaucracy and the absence of technical and economic data which will guarantee the financial viability of a centralized treatment unit.

Cost-benefit analysis of a circular economy project: a study on a recycling system for end-of-life tyres

End-of-life vehicles (ELV) represent a relevant waste source in Europe, even if ELV recycling is a priority of the European Union waste legislation and Environment Action Programmes (EAPs). End-of-Life Tires (ELTs) constitute a relevant portion of ELV waste. Textile fibre, which is a relevant portion of the ELT material, is considered as a special waste (European Waste Catalogue – EWC code 19.12.08). The main problem related to textile fibre is its contamination with rubber which does not allow to obtain a pure product economically and qualitatively useable.The aim of this paper is to illustrate an innovative technology for ELT fibre's recycling, which allows to transform textile fibre into a useful secondary raw material for different applications.In particular, the use of ELT fibre as additive for bituminous conglomerates has been investigated. The different processes have been analysed from an environmental point of view, applying the Life Cycle Assessment methodology. It came up there is an impact reduction in case the ELT fibre is reused as additive for bituminous conglomerates, instead of disposing it (through incineration).Moreover, the financial and economic sustainability of the related technological process has been evaluated to check whether the process is sustainable in the long term. Starting from the results of the Life Cycle Assessment, economic performance indicators have been calculated, by applying the European Commission methodology for cost-benefit analysis. According to the present cost-benefit analysis, in the medium and long term the system is financially viable, and the high economic profitability makes the process economically sustainable. Furthermore, a sensitivity analysis as well as a risk assessment have been carried out in order to identify critical variables, evaluate risks and define risk mitigation measures. According to the sensitivity analysis performed, the project is not highly risky since even in the worst scenario the possible loss is moderate.Based on the results of this analysis, it can be concluded that this ELT fibre's recycling system can be replicated across Europe, conveniently fostered by national policies (such as subsidies, value added tax etc.).

Defining the process of including sustainable rubber particles under sleepers to improve track behaviour and performance

The inclusion of rubber particles derived from end-of-life tyres (ELTs) under the sleepers has been demonstrated in previous studies to be a potential solution to improve the behaviour and durability of railway tracks, and then, minimizing the negative impacts associated with the need for maintenance. Nonetheless, more in-depth studies are still required to define the optimal procedure prior to its application in real tracks. The present paper therefore focused on assessing the main parameters for defining the procedure for adding rubber particles to create an elastic layer under sleepers through a two-step stoneblowing process. Such parameters included the size of the rubber particles; the position of the elastic layer (above or below the conventional small aggregates used in the stoneblowing process); the need to compact the first layer before injecting the subsequent one; the effect of rubber dosage; and the impact of service conditions (traffic levels and temperatures). For this purpose, a number of laboratory tests were carried out on testing boxes simulating the effects of train passages, assessing diverse properties such as particles percolation, section settlement, stiffness and dissipated energy. The results revealed that the inclusion of rubber particles (ranging between 14 and 20 mm) as an elastic layer over the compacted small stones through a two-step stoneblowing process, provides an effective solution to graduate and optimize global track behaviour by using different quantities of rubber, which could reduce the need for track maintenance and its environmental impacts.

End‐of‐life product management as a resilience driver for developing countries: A policy experiment for used tires in Ecuador

AbstractOver the last decades, a number of new environmental policies have been designed to improve waste management. Among them, extended producer responsibility (EPR) has introduced a mechanism to shift the environmental and financial burden of end‐of‐life products from public management to producers. Recently, EPR has been adopted by a growing number of developing countries, but this policy often struggles in being effectively implemented in such contexts, missing the opportunity of using waste management as a sustainability driver. By discussing the EPR for end‐of‐life tires (ELTs) in Ecuador, this paper proposes a different approach in designing and implementing EPR schemes in developing countries: it recommends consideration of social sustainability, rather than merely copying foreign management frameworks. To address this point, two case studies on socially directed ELT applications were designed and carried out. The case studies aimed at improving resilience of vulnerable populations to natural disasters by increasing the resistance of housing and settlements against catastrophic events using civil engineering applications. The analysis of the case studies’ outcomes brings to light possible policy adjustments, in which social sustainability goals are taken into account within the national EPR scheme. The Ecuadorian case also highlights the benefit of employing an adaptive governance approach when dealing with challenging urban management topics, such as informality (a widespread phenomenon in developing countries) and resilience.

Reuse of carbon black from end-of-life tires in new pneumatic formulations and life-cycle assessment of the thermolysis process

Carbon black derived from end-of-life tires (ELTs) through thermolysis process was studied. The main attraction of this material is the low market price (€450 ton−1) compared with virgin carbon black (about €700 ton−1). Investigation was focused on the vulcanization reaction of rubber with the addition of both types of carbon black, that is, carbon black recycled (CBr) from the thermolysis of ELTs and carbon black virgin (CBv) from traditional oil process. The aim of the research was to verify that CBr has similar reactivity than CBv when blended with rubber and vulcanized. Furthermore, environmental benefits of recovering CBr and the other coproducts were evaluated by means of the life-cycle assessment methodology.