Uncertainty calculation in life cycle assessments

Goal and Background  Uncertainty is commonly not taken into account in LCA studies, which downgrades their usability for decision support. One often stated reason is a lack of method. The aim of this paper is to develop a method for calculating the uncertainty propagation in LCAs in a fast and reliable manner. Approach  The method is developed in a model that reflects the calculation of an LCA. For calculating the uncertainty, the model combines approximation formulas and Monte Carlo Simulation. It is based on virtual data that distinguishes true values and random errors or uncertainty, and that hence allows one to compare the performance of error propagation formulas and simulation results. The model is developed for a linear chain of processes, but extensions for covering also branched and looped product systems are made and described. Results  The paper proposes a combined use of approximation formulas and Monte Carlo simulation for calculating uncertainty in LCAs, developed primarily for the sequential approach. During the calculation, a parameter observation controls the performance of the approximation formulas. Quantitative threshold values are given in the paper. The combination thus transcends drawbacks of simulation and approximation. Conclusions and Outlook  The uncertainty question is a true jigsaw puzzle for LCAs and the method presented in this paper may serve as one piece in solving it. It may thus foster a sound use of uncertainty assessment in LCAs. Analysing a proper management of the input uncertainty, taking into account suitable sampling and estimation techniques; using the approach for real case studies, implementing it in LCA software for automatically applying the proposed combined uncertainty model and, on the other hand, investigating about how people do decide, and should decide, when their decision relies on explicitly uncertain LCA outcomes-these all are neighbouring puzzle pieces inviting to further work.     

Comparing life cycle assessments of different biofuel options

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Highlights► Biofuel LCAs have high uncertainty and variability, particularly prospective LCAs. ► Variability in biofuel LCAs has two sources: model and methods-induced, and real. ► LCAs of 2nd-generation fuels are so uncertain that no pathway can clearly be preferred. ► Algae biodiesel LCA has greatest variability due to diverse technology, assumptions.     

Addressing the effect of social life cycle assessments

Purpose

In the recently published ??Guidelines for social life cycle assessment of products??, it is stated that the ultimate objective of developing the social life cycle assessment (SLCA) is to promote improvements of social conditions for the stakeholders in the life cycle. This article addresses how the SLCA should be developed so that its use promotes these improvements.

Methods

Hypotheses of how the use of SLCA can promote improvement of social conditions in the life cycle are formulated, after which theories and empirical findings from relevant fields of research are used to address the validity of these hypotheses.

Results

Three in some cases potentially overlapping SLCA approaches are presented, assumed to create a beneficial effect in the life cycle in different ways. However, empirical and theoretical findings show that the beneficial effects proposed to arise from the use of each of these three approaches may all be problematic. Some of these problems may be mitigated through methodological modifications.

Conclusions

Given the significant problems in relation to creating an effect through the use of the SLCAs, and given the significant practical problems in applying the SLCAs, it is questioned whether the development of SLCA is a fruitful approach for improving social conditions in the product life cycle.     

Modeling process and material alternatives in life cycle assessments

Background, Aims and Scope  Although LCA is frequently used in product comparison, many practitioners are interested in identifying and assessing improvements within a life cycle. Thus, the goals of this work are to provide guidelines for scenario formulation for process and material alternatives within a life cycle inventory and to evaluate the usefulness of decision tree and matrix computational structures in the assessment of material and process alternatives. We assume that if the analysis goal is to guide the selection among alternatives towards reduced life cycle environmental impacts, then the analysis should estimate the inventory results in a manner that: (1) reveals the optimal set of processes with respect to minimization of each impact of interest, and (2) minimizes and organizes computational and data collection needs. Methods  A sample industrial system is used to reveal the complexities of scenario formulation for process and material alternatives in an LCI. The system includes 4 processes, each executable in 2 different ways, as well as 1 process able to use 2 different materials interchangeably. We formulate and evaluate scenarios for this system using three different methods and find advantages and disadvantages with each. First, the single branch decision tree method stays true to the typical construction of decision trees such that each branch of the tree represents a single scenario. Next, the process flow decision tree method strays from the typical construction of decision trees by following the process flow of the product system, such that multiple branches are needed to represent a single scenario. In the final method, disaggregating the demand vector, each scenario is represented by separate vectors which are combined into a matrix to allow the simultaneous solution of the inventory problem for all scenarios. Results  For both decision tree and matrix methods, scenario formulation, data collection, and scenario analysis are facilitated in two ways. First, process alternatives that cannot actually be chosen should be modeled as sub-inventories (or as a complete LCI within an LCI). Second, material alternatives (e.g., a choice between structural materials) must be maintained within the analysis to avoid the creation of artificial multi-functional processes. Further, in the same manner that decision trees can be used to estimate ‘expected value’ (the sum of the probability of each scenario multiplied by its ‘value’), we find that expected inventory and impact results can be defined for both decision tree and matrix methods. Discussion  For scenario formulation, naming scenarios in a way that differentiate them from other scenarios is complex and important in the continuing development of LCI data for use in databases or LCA software. In the formulation and assessment of scenarios, decision tree methods offer some level of visual appeal and the potential for using commercially available software/ traditional decision tree solution constructs for estimating expected values (for relatively small or highly aggregated product systems). However, solving decision tree systems requires the use of sequential process scaling which is difficult to formalize with mathematical notation. In contrast, preparation of a demand matrix does not require use of the sequential method to solve the inventory problem but requires careful scenario tracking efforts. Conclusions  Here, we recognize that improvements can be made within a product system. This recognition supports the greater use of LCA in supply chain formation and product research, development, and design. We further conclude that although both decision tree and matrix methods are formulated herein to reveal optimal life cycle scenarios, the use of demand matrices is preferred in the preparation of a formal mathematical construct. Further, for both methods, data collection and assessment are facilitated by the use of sub-inventories (or as a complete LCI within an LCI) for process alternatives and the full consideration of material alternatives to avoid the creation of artificial multi-functional processes. Recommendations and Perspectives  The methods described here are used in the assessment of forest management alternatives and are being further developed to form national commodity models considering technology alternatives, national production mixes and imports, and point-to-point transportation models. ESS-Submission Editor: Thomas Gloria, PhD (t.gloria@fivewinds.com)     

Assessing the availability of life cycle assessments in Austria

The International Journal of Life Cycle Assessment - This study aims to present the availability of studies that are related to life cycle assessments (LCA) in Austria since 2000. This study also...     

Comparative life cycle assessments of incineration and non-incineration treatments for medical waste

Background, aim, and scope  Management of the medical waste produced in hospitals or health care facilities has raised concerns relating to public health, occupational safety, and the environment. Life cycle assessment (LCA) is a decision-supporting tool in waste management practice; but relatively little research has been done on the evaluation of medical waste treatment from a life cycle perspective. Our study compares the environmental performances of two dominant technologies, hazardous waste incineration (HWI) as a type of incineration technology and steam autoclave sterilization with sanitary landfill (AL) as a type of non-incineration technology, for specific medical waste of average composition. The results of this study could support the medical waste hierarchy. Materials and methods  This study implemented the ISO 14040 standard. Data on steam autoclave sterilization were obtained from an on-site operations report, while inventory models were used for HWI, sanitary landfill, and residues landfill. Background data were from the ecoinvent database. The comparative LCA was carried out for five alternatives: HWI with energy recovery efficiencies of 0%, 15%, and 30% and AL with energy recovery efficiencies of 0% and 10%. Results  The assumptions on the time frame for landfill markedly affect the impact category scores; however, the orders of preference for both time frames are almost the same. HWI with 30% energy recovery efficiency has the lowest environmental impacts for all impact categories, except freshwater ecotoxicity. Incineration and sanitary landfill processes dominate global warming, freshwater aquatic ecotoxicity, and eutrophication of incineration and non-incineration alternatives, respectively. Dioxin emissions contribute about 10% to human toxicity in HWI without energy recovery alternatives, and a perturbation analysis yielded identical results. As regards eutrophication, non-incineration treatments have an approximately sevenfold higher impact than incineration treatments. Discussion  The differences between short-term and long-term time frame assumptions mainly are decided by heavy metals dissolved in the future leachate. The high heat value of medical waste due to high contents of biomass, plastic, and rubber materials and a lower content of ash, results in a preference for incineration treatments. The large eutrophication difference between incineration and non-incineration treatments is caused by different N element transformations. Dioxin emission from HWI is not the most relevant to human toxicity; however, large uncertainties could exist. Conclusions  From a life cycle perspective, the conventional waste hierarchy, implying incineration with energy recovery is better than landfill, also applies to the case of medical waste. The sanitary landfill process is the key issue in non-incineration treatments, and HWI and the subsequent residues landfill processes are key issues in incineration treatments. Recommendations and perspectives  Integrating the medical waste hierarchy and constructing a medical waste framework require broader technologies to be investigated further, based on a life cycle approach. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A review of life cycle assessments on wind energy systems

Purpose

Several life cycle assessments (LCAs) of wind energy published in recent years are reviewed to identify methodological differences and underlying assumptions.

Methods

A full comparative analysis of 12 studies were undertaken (ten peer-reviewed papers, one conference paper, and one industry report) regarding six fundamental factors (methods used, energy use accounting, quantification of energy production, energy performance and primary energy, natural resources, and recycling). Each factor is discussed in detail to highlight strengths and shortcomings of various approaches.

Results

Several potential issues are found concerning the way LCA methods are used for assessing energy performance and environmental impact of wind energy, as well as dealing with natural resource use and depletion. The potential to evaluate natural resource use and depletion impacts from wind energy appears to be poorly exploited or elaborated on in the reviewed studies. Estimations of energy performance and environmental impacts are critically analyzed and found to differ significantly.

Conclusions and recommendations

A continued discussion and development of LCA methodology for wind energy and other energy resources are encouraged. Efforts should be made to standardize methods and calculations. Inconsistent use of terminology and concepts among the analyzed studies are found and should be remedied. Different methods are generally used and the results are presented in diverse ways, making it difficult to compare studies with each other, but also with other renewable energy sources.     

Accounting for correlational structures in stochastic comparative life cycle assessments through copula modeling

The International Journal of Life Cycle Assessment - The presence of correlations between input parameters in a life cycle assessment (LCA) is a well-known issue. On top of that, the univariate...     

Cell cycle: check for asynchrony

During metazoan development cells destined for different fates become asymmetric, not just in morphology and developmental potential but also in cell-cycle timing. A recent study has now shown that differential cell-cycle timing in the first cell divisions of the Caenorhabditis elegans embryo is in part controlled by a DNA replication checkpoint.     

Accounting for spatial variability in life cycle cost-effectiveness assessments of environmental impact abatement measures

The International Journal of Life Cycle Assessment - The environmental and economic impacts of livestock production systems are typically assessed using global characterisation factors and data,...     

Scientometric sorting by importance for literatures on life cycle assessments and some related methodological discussions

Purpose

This paper aims to sort the literatures on life cycle assessments (LCA) by their respective importance through citation and co-citation analysis and to further discuss the strengths and weaknesses of these kinds of scientometric methods in the case of LCA research.

Methods

CiteSpace II was used to generate document co-citation networks based on 3,824 articles retrieved from the ISI Web of Science database on this topic.

Results

Table 1 provides the top 50 highest cited documents in the LCA field. Here, we use two indicators, i.e., citation frequency in citation analysis and betweenness centrality metric in co-citation analysis, to measure the importance of these LCA literatures.

Conclusions

Citation and co-citation analysis are useful for environmental scientists and engineers to get a better understanding of the inner structure of LCA research. However, like all other research methods, this kind of analysis has some limitations. On the one hand, Scientometric studies and related software are very dependent on ISI Web of Science database, but considering the ISI Web of Science only began to track the LCA field fairly recently, the Scopus database would probably give a fuller picture. On the other hand, since the essence of scientometrics analysis is outsiders commenting insiders, so with only citation and co-citation analysis, to our understanding of the past, present, and future of LCA field, is insufficient.     

Reference situations for biodiversity in life cycle assessments: conceptual bridging between LCA and conservation biology

The International Journal of Life Cycle Assessment - In life cycle assessment (LCA) literature addressing land use impacts on biodiversity, several potential reference situations are proposed....     

Review: life cycle assessments in Nigeria,Ghana, and Ivory Coast

Purpose

Life cycle assessments (LCAs) are considered common quantitative environmental techniques to analyze the environmental impact of products and/or services throughout their entire life cycle. A few LCA studies have been conducted in West Africa. This study aimed to discuss the availability of LCA (and similar) studies in Nigeria, Ghana, and Ivory Coast.

Methods

An online literature review of reports published between 2000 and 2016 was conducted using the following keywords: “life cycle assessment,” “carbon footprinting,” “water footprinting,” “environmental impact,” “Nigeria,” “Ghana” and “Ivory Coast.”

Results and discussion

A total of 31 LCA and environmental studies in Nigeria, Ghana, and Ivory Coast were found; all but one were conducted after 2008. These were mainly academic and most were publicly available. The industries studied included energy sector, waste management, real estate, food sector, and others such as timber and gold. The minimal number of studies on LCAs and environmental impacts in these West African states could be because companies are failing to promote quantitative environmental studies or studies are kept internally for the use of other assessment techniques. Furthermore, it could be that academic research institutions lack cutting-edge research resources for LCA, environmental impact, carbon, and water footprinting studies.

Conclusions

Further quantitative environmental studies should be conducted in Nigeria, Ghana, and Ivory Coast to increase the understanding of environmental impacts. In these countries, the existence of LCA studies (and by association the localized life cycle inventory (LCI) datasets) is crucial as more companies request this information to feed into background processes.

     

Evaluation and selection of functional diversity metrics with recommendations for their use in life cycle assessments

The International Journal of Life Cycle Assessment - In life cycle assessments (LCAs), the focus of modelling the impact of human-induced pressures on biodiversity has been mainly on taxonomic...     

A general framework for including biogenic carbon emissions and removals in the life cycle assessments for forestry products

The International Journal of Life Cycle Assessment -     

On the calculation of fuel savings through lightweight design in automotive life cycle assessments

Background, aim, and scope  

Lightweight design is a common means of reducing a passenger car's fuel consumption. In order to calculate the resulting fuel savings, one has to estimate the total energy that is needed to move a certain weight over a defined distance in a distinct way, and express this energy in liter of gasoline or diesel. This can be accomplished by the so-called fuel reduction value (FRV) and based on a standardized driving cycle, e.g., the New European Driving Cycle (NEDC). The aim of this paper is to explain the theoretical background of the calculation of fuel savings in automotive lightweight life cycle assessments (LCAs) of internal combustion engine (ICE) vehicles in greater detail than it has been done before, to describe the resulting factors and their different applications, and to point out some notable particularities that need to be taken into account when conducting this type of LCA study.     

(Sprayed) concrete production in life cycle assessments: a systematic literature review

The International Journal of Life Cycle Assessment - The carbon intensity that accompanies concrete manufacturing has been widely investigated. However, depending on the intended use,...