Input Flow Research Articles

INFLUENCE OF INFLOW SEWAGE CHARACTERISTICS ON THE PERFORMANCE OF TAHTA WASTE STABILIZATION PONDS IN COMPARISON WITH THE DESIGN ONES

TAHTA waste water treatment plant is a (WSPs) constructed for treatment the domestic waste water of TAHTA city which located at a latitude of 26˚42' N and a longitude of 31˚41'E and it is about 91.00 m above the sea level. The performance of TAHTA plant along the three years of study period is estimated in the form of a comparison between the results of the total system or its components with the allowable values of the studied parameters, or in a relation between the input and the output of these parameters as efficiency. The final effluent characteristics are compared with the designed ones and with those recommended by Egyptian Code of Practice (ECP) and Food and Agriculture Organization (FAO) for re-use of water treated by this type of treatment. The existing operation is considered as unrealistic because of the deviation of its input flow parameters from the designed ones. The plant ponds were designed for full capacity flow rates, recommended influent BOD, etc. So, this research aiming to: 1) Evaluate the performance of the plant under existing operation conditions. 2) Examine whether the treated water quality in the range of standards set by (ECP) for this type of treatment. 3) Identify the problems associates with the plant. 4) Suggest ways to improve the performance of the treatment plant. The study is performed experimentally where the daily sampling and laboratory analysis were carried out according the standard specifications. The study revealed that 1) Plant system is working satisfactory in the period of study to fulfil the requirement of use its treated water in irrigating forest trees which is the one of its construction purposes. 2) As the performance of the plant did not meet the design one at the operation parameters such as low flow rate and low coming BOD5 loadings for treating some parameters due to sludge accumulation in anaerobic ponds, or because the incoming rate of sewage in 2016 is higher than the plant design capacity. So; a) Sludge accumulated in anaerobic ponds should be removed when its depth reaches 1.00 m according the design recommendations or when it is one half full of the sludge by volume [13]. b) Flow distribution should be checked to be uniform otherwise a short circuiting problem is faced. c) Inflow rate must be checked otherwise, to receive more of sewage inflow coming from the surround area than its design capacity some modifications may be used to improve (WSPs) efficiency. 3) According to (ECP) and (FAO) recommendation, the treated wastewater from TAHTA plant is acceptable for re-used in the irrigation of wooden tree forests.

Experimental investigation of hydrogen production by CH4–CO2 reforming using rotating gliding arc discharge plasma

Hydrogen produced from CH4–CO2 reforming by an optimized rotating gliding arc discharge plasma reactor is investigated in this study. The effect of CH4/CO2 ratio (mole ratio), total input flow rate, discharge gap, voltage, and discharge frequency are analyzed. The results show that H2 yield increases with the increase of CH4/CO2 ratio. Arc can be stretched effectively by increasing total input flow rate, then the discharge region is enlarged. Increasing discharge gap can enlarge the discharge region, but the reaction of the gas mixture would be suppressed if the discharge region was excessively large. The discharge region decreases with the increased discharge frequency to a certain degree. Based on the experimental results, the optimal experimental condition is concluded as applied voltage 60 V, discharge frequency 20 kHz, and minimum discharge gap 3 mm. It is anticipated that the results would serve as a good guideline to the application of hydrogen production from hydrocarbon fuels by plasma reforming onboard.

Hydrodynamic Microparticle Separation Mechanism Using Three-Dimensional Flow Profiles in Dual-Depth and Asymmetric Lattice-Shaped Microchannel Networks.

We herein propose a new hydrodynamic mechanism of particle separation using dual-depth, lattice-patterned asymmetric microchannel networks. This mechanism utilizes three-dimensional (3D) laminar flow profiles formed at intersections of lattice channels. Large particles, primarily flowing near the bottom surface, frequently enter the shallower channels (separation channels), whereas smaller particles flowing near the microchannel ceiling primarily flow along the deeper channels (main channels). Consequently, size-based continuous particle separation was achieved in the lateral direction in the lattice area. We confirmed that the depth of the main channel was a critical factor dominating the particle separation efficiencies, and the combination of 15-μm-deep separation channels and 40-μm-deep main channels demonstrated the good separation ability for 3–10-μm particles. We prepared several types of microchannels and successfully tuned the particle separation size. Furthermore, the input position of the particle suspension was controlled by adjusting the input flow rates and/or using a Y-shaped inlet connector that resulted in a significant improvement in the separation precision. The presented concept is a good example of a new type of microfluidic particle separation mechanism using 3D flows and may potentially be applicable to the sorting of various types of micrometer-sized objects, including living cells and synthetic microparticles.

РОЗПОДІЛ РЕСУРСІВ БАГАТОФАЗНОЇ СИСТЕМИ ОБРОБКИ ВЕЛИКИХ ДАНИХ ПРИ ВИСОКОІНТЕНСИВНОМУ ВХІДНОМУ ПОТОЦІ

Завдання оптимального проектування багатофазної системи обробки великих даних (БФСОВД) при високоінтенсивному вхідному потоці потребують застосування сучасних математичних і комп'ютерних методів та засобів. Предметом дослідження є ресурси багатофазної системи обробки великих даних. Мета дослідження – розроблення методу оптимального розподілу ресурсів БФСОВД при високоінтенсивному вхідному потоці, котрий враховує як можливість проведення аналізу даних у режимі реального часу, так і особливостей високоінтенсивного потоку вхідних даних із багатьох джерел. Результати. Визначено особливості високоінтенсивних потоків вхідних даних та показана можливість апроксимації його з достатньою точністю гауссівським розподілом. Також визначені особливості функціонування багатофазних систем та запропонована схема функціонування багатофазної системи обробки великих даних. Базуючись на отриманих результатах розроблена математична модель процесу оптимізаціі розподілу ресурсів багатофазної системи обробки великих даних при високоінтенсивному вхідному потоці. Для цього використано метод динамічного програмування. Висновок. В результаті отримана мінімальна кількість каналів в кожній фазі БФСОВД, при якій середній час аналізу даних в системі буде мінімальним.

The service-stock trap: analysis of the environmental impacts and productivity of the service sector in Hungary

Urbanization and the emerging share of the service sector in economic output may support the sustainability transition due to lower material input and emissions, while further accelerating the economic growth at the same time. Nevertheless, there are significant barriers to the transition. In this study, the service sector of Hungary and its four commercial sub-sectors have been analyzed with regard to their material requirement (input flows and stock) and greenhouse gas emissions (GHG) emissions utilizing EXIOBASE v3. General policy implications are also provided with special regard to costs, possible taxes and productivity of resources. The share of direct and indirect GHG emissions and material input generated by the sector was stable and moderate. A permanently improving trend is present in GHG, and material input intensity. Material stock accumulation in the service sector (capital stock), however, shows an ascending trend, and it has increased from 42% in 1995 to be 55% in 2015. Material input productivity of investments into services has increased until the economic crisis, then it starts to decline or stagnate; while overall stock productivity has decreased in two sub-sectors, and slow improvement was observable in sub-sectors of transportation and information and communication technology (ICT). Stock productivity of ICT and machinery capital stock was decreased dramatically in all sub-sectors. Four economic sub-sectors of the commercial services analyzed in this study have increased their capital stock from 130 to 288 Mt between 2000 and 2015. The exponential trend in material stock accumulation is an environmental issue with rising scientific concern and awareness, since it constitutes the basis of crucial waste management, resource scarcity and resource use challenges in the future. The current study indicates general reinforcement of the environmental pressure of material stock accumulation by the service sector. This phenomena was defined as the ‘service-stock trap’, which refers to the sign of a trade-off between the descending flow-type environmental impacts and ascending impacts of capital stock accumulation during the economic transition towards a service-based economy. As a promising way out of the trap, the resource tax was discussed in detail, which seems to be suitable for forming investment decisions of the business actors.

Plasma catalytic steam methane reforming for distributed hydrogen production

Abstract Steam methane reforming (SMR) via thermal catalytic approach is one of the dominant sources of industrial hydrogen, however it proceeds with slow response and low specific productivity. Here we demonstrate a plasma catalytic SMR for distributed hydrogen production, for which warm plasma by gliding arc discharge initiates the reaction, followed by Ni-based catalyst in a heat-insulated reactor without extra heating. In terms of the plasma alone process, specific energy input (SEI), steam/CH4 ratio (S/C) and total inlet flow rate (Ft) contribute to the methane conversion. In parallel, SEI and S/C account for the decrease in C2Hx selectivity hence the increase in selectivity of CO and CO2, while with Ft all the selectivity is approximately constant. The reaction pathway represented by the selectivity can be influenced by SEI and S/C rather Ft. To utilize the heat and active species with the reaction in plasma zone, Ni/CeO2/Al2O3 catalyst bed is coupled. For the coupled process, the conversion approaches the thermodynamic equilibrium values, with the favorable dismissed C2Hx selectivity thus the complete selectivity to CO and CO2. The coupled process was maintained steady for six hours, and the methane conversion of 90% at total hydrogen (t-H2) production rate of 2.7 SLM is achieved under optimum conditions of SEI, S/C, Ft and gas hourly space velocity (GHSV) of 110 kJ/mol, 3, 3 SLM and 18,000 ml·g−1 h−1. Compared to 59% and 2.3 kW h/Nm3 of the plasma alone process, such a coupled process achieves the energy efficiency (of methane to t-H2) of 75% and the low energy cost of 1.5 kW h/Nm3. Consequently, our approach of plasma catalytic SMR features the merits of rapid response, compact system and high specific productivity, which can be anticipated for the emerging needs of distributed hydrogen generation.

Random and stochastic disturbances on the input flow in chemostat models with wall growth

In this paper, we analyze a chemostat model with wall growth where the input flow is perturbed by two different stochastic processes: the well-known standard Wiener process, which leads into several drawbacks from the biological point of view, and a suitable Ornstein-Uhlenbeck process depending on some parameters which allow us to control the noise to be bounded inside some interval that can be fixed previously by practitioners. Thanks to this last approach, which has already proved to be very realistic when modeling other simplest chemostat models, it will be possible to prove the persistence and coexistence of the species in the model without needing the theory of random dynamical systems and pullback attractors needed when dealing with the Wiener process. This is an advantage since the theoretical framework in this paper is much less complicated and provides us much more information than the other.

COMPARISON OF ENERGY FLOW STREAM AND ISENTROPIC METHOD FOR STEAM TURBINE ENERGY ANALYSIS

In this paper, a comparison of two different methods for a steam turbine energy analysis is presented. A high-pressure steam turbine from a supercritical thermal power plant (HPT) was analysed at three different turbine loads using the energy flow stream (EFS) method and isentropic (IS) method. The EFS method is based on steam turbine input and output energy flow streams and on the real steam turbine produced power. The method is highly dependable on the steam mass flow rate lost through the turbine gland seals. The IS method is based on a comparison of turbine steam expansion processes. Observed energy analysis methods cannot be directly compared because they are based on different sources of steam turbine energy losses, so, an overall steam turbine energy analysis is presented. Unlike most steam turbines from the literature, the analysed HPT did not have the highest overall energy efficiency at a full load due to exceeding the water/steam critical pressure at the turbine inlet during such operation.

A Study on Microstructure and Mechanical Properties of Micro Friction Stir Welded Ultra-Thin Al-1060 Sheets by the Shoulderless Tool

The welding tool is the key of micro friction stir welding (μFSW), which affects the heat input and the plastic forming of weld metal. In this paper, 0.8-mm-thick ultra-thin 1060-H24 aluminum sheets μFSW butt joints were used to compare and analyze the influence of the conventional tool and shoulderless tool on weld shaping, microstructure and mechanical properties. Besides, by measuring the axial force, transverse force and weld temperature in μFSW process, the influence of these two different tools on the heat input and metal flow mechanism of the weld were analyzed. The results show that the weld generated by the shoulderless tool has narrower width, less heat input and metal involved in plastic forming resulting in smaller HAZ (heat affected zone). The hardness of NZ (nugget zone) is obviously increased compared with that of the base metal. The highest tensile strength can reach 108.6 MPa, accounting for 78.6% of the base metal and 117.3% of the joint by the conventional tool. But the welding defects have to be overcome for industrial application of the shoulderless tool.

Separation of BTX chemicals from biomass pyrolysis oils via continuous flash distillation

Partially deoxygenated pyrolysis oils, such as those produced by tail gas reactive pyrolysis (TGRP), show promise for use in biorefineries if they can integrate into standard refinery operations, one of which is distillation. A feasible method for modeling the process and for removing aqueous components will advance progress. This study investigated the potential of continuous flash distillation for fractionating partially deoxygenated bio-oil component chemicals benzene, toluene, and xylene (BTX), which are critical feedstocks for producing many refinery products. A model bio-oil mixture was used to evaluate process performance, and process conditions were investigated with respect to separation efficiency (temperature = 120, 130, and 140 °C; input flow rate = 2 or 3 mL min−1). Mean BTX yield (gout gin−1) for an oil flow rate of 2 mL min−1 ranged between 0.134 and 0.222 gout gin−1, while for 3 mL min−1 yields ranged from 0.135 to 0.400 gout gin−1. In all treatments, the measured amounts of BTX from model bio-oil were less than those from ASPEN simulations. From the distillates, aqueous fractions phase separated while sequestering acetic acid from the organics. Residence time within the drum was positively correlated with concentration of BTX in the distillates. At no point did solid residues form within the flash drum. When compared with analogous experiments at optimal conditions, BTX yields from real TGRP oil were comparable but less than the analogous model experiment. These results suggest that continuous, atmospheric pressure distillation of low-oxygen bio-oils can be used for separating commodity, refinery-grade chemicals such as BTX from biomass pyrolysis-derived bio-oils.

Implementation of an urban efficiency index to comprehend post-metropolitan territories—The case of Greater Milan in Italy

The objective of this research is to develop a large-scale interdisciplinary urban analysis of a post-metropolitan area in Northern Italy and provide outcomes that can be useful for policymakers, public utilities, urban designers, and other stakeholders in defining strategies to improve the territory. This research, implemented within a wide national academic study on several urban regions in Italy, focuses on a 100 × 100 km2 square territory around the centre of Milan that encompasses 904 municipalities. The main local input and output flows are analysed for each municipality by considering available databases. Urban performance is investigated in the research framework of urban metabolism, by applying a fuzzy logic model. The overall structure of the model, definition of subsystems, set of indicators, adopted benchmarks, and levels of importance of variables are calibrated to suit the particular context of applications.The model provides the UEI (urban efficiency index) outcome and a geographical information system (GIS) representation to facilitate the comparison between municipalities and territories and determine the low or high-performance areas that necessitate further investigations.This work represents an important attempt in developing and applying methods for supporting decisions and defining policies towards more sustainable urban areas.

RESEARCH OF QUEUEING SYSTEMS WITH SHIFTED ERLANGIAN AND EXPONENTIAL INPUT DISTRIBUTIONS

Context. In queuing theory, the study of G/G/1 systems is particularly relevant due to the fact that until now there is no solution in the final formin the general case. The problem of the derivation in closed form of the solution for the average waiting time in the queue for ordinary systems witherlangian and exponential input distributions and for the same systems with shifted distributions is considered.Objective. Obtaining a solution for the main system characteristic – the average waiting time for queue requirements for three types of queuingsystems of type G/G/1 with conventional and shifted erlangian and exponential input distributions.Method. To solve this problem, we used the classical method of spectral decomposition of the solution of Lindley integral equation, which allowsone to obtain a solution for average the waiting time for systems under consideration in a closed form. The method of spectral decomposition ofthe solution of Lindley integral equation plays an important role in the theory of systems G/G/1. For the practical application of the results obtained,the well-known method of moments of probability theory is used.Results. The spectral decompositions of the solution of the Lindley integral equation for the three kinds of systems were first obtained with thehelp of which the calculated expressions for the average waiting time in the queue for the above systems in a closed form were derived.Conclusions. The introduction of the time shift parameter in the laws of input flow distribution and service time for the systems under considerationturns them into systems with a delay with a shorter waiting time. This is due to the fact that the time shift operation reduces the coefficient ofvariation in the intervals between the receipts of the requirements and their service time, and as is known from queuing theory, the average wait timeof requirements is related to these coefficients of variation by a quadratic dependence. The system with erlangian input distributions of the secondorder is applicable only at a certain point value of the coefficients of variation of the intervals between the receipts of the requirements and their servicetime. The same system with shifted distributions allows us to operate with interval values of coefficients of variations, which expands the scopeof these systems. Similarly the situation and with the shifted exponential distributions is. In addition, the shifted exponential distribution contains twoparameters and allows one to approximate arbitrary distribution laws using the first two moments. This approach allows us to calculate the averagelatency for these systems in mathematical packages for a wide range of traffic parameters. All other characteristics of the systems are derived from thewaiting time. The method of spectral decomposition of the solution of the Lindley integral equation for the systems under consideration makes itpossible to obtain a solution in a closed form and these solutions are published for the first time.

Inherited learning in a system of minimum dissipation: The case of the Yumhu of Ixtenco-Mexico

Introduction This article aims to show the way in which a social system of minimum dissipation -like the Yumhu of Ixtenco- has the capacity to counteract its entropic levels avoiding reaching thermal death, due to the type of non-formal learning that is developed in this and its way of reproducing. In this regard, Objective was to identify the forms of non-formal learning in the social system of minimum dissipation of the Yumhu of Ixtenco that in a contrasting, dynamic and changing environment has been able to provide the Yumhu adapt and survive in time despite the weakening of its energy potential. Materials and methodsused was qualitative with ethnographic tools applied to seven research subjects. The main Results point to the fact that non-formal learning in the Yumhu system happens under the principles of an indigenous pedagogy of low dissipation, which allows the survival of the system. The main Conclusions are that learning takes place from an inherited base that the Yumhu have used to preserve themselves over time, due to their functioning as a minimal dissipation system, which weakens their energetic potential (such as information) Discussion in proportion to their input flows, which allows them to adapt to their context with minimal energy reaching a stable state.

DATA PAPERS AS A FORM OF SECONDARY SCIENTIFIC INFORMATION SOURCES

Data papers are a form of metadata publications in peer-reviewed scientific journals and are considered as secondary sources of scientific and technical information (STI). The specificity of data finding and collecting in the field of grey literature (GL) and, in particular, GL devoted to STI is characterized. The sources of data concerning the input flow of documents (scientific and technical reports and dissertations) to the Federal GL Information System are described. The data is open for a potential reuse once properly obtained from the System.

Spray, Combustion and Soot of Water-in-Fuel (n-Dodecane) Emulsions in a Constant Volume Combustion Chamber; Part II: Effects of Low Temperature Conditions and Oxygen Concentrations

The application of water-in-fuel (n-dodecane) emulsions (WFE) with a fixed water mass fraction of 10 wt% has been investigated in an optically accessible constant volume combustion chamber (CVCC) at varying low ambient temperatures conditions (Tgas=760–800K/ρgas=22.8kg/m3) such as found in direct-injection (DI) Diesel engine operations with (extreme) “Miller”-timing. Furthermore, oxygen concentrations have been decreased to 18 vol% and 15 vol% in order to emulate exhausRd in DI engines.As in Part I two injection strategies have been employed: first, a constant injection pressure case as for neat fuel and prolonged injection duration (strategy (A)), second, the injection pressure has been increased to keep a constant energy input flow, therefore, with constant injection duration (strategy (B)).Spray parameters and combustion characteristics have been assessed by Schlieren imaging, Mie-scattering, diffused back-illumination extinction imaging (DBIEI) and OH∗-chemiluminescence, respectively. Furthermore, the spray flame’s soot formation has been investigated through the detection of soot incandescence signals.For the WFE liquid lengths (LL) penetrate farther downstream the respective LOL at all ambient conditions, whereas, utilizing neat n-dodecane LLs remain upstream the LOL. The interaction between LL and the high-temperature reaction zone dominates the soot behaviour of WFE resulting in decreased dwell times between ignition and first soot occurrence. Decreasing gas temperatures at atmospheric oxygen concentrations generally decrease dwell times, even though, ignition delays and LOLs increase by the utilization of neat n-dodecane.Soot incandescence signal amplitudes decrease strongly employing WFE (150–270 times lower maximum signal values) compared to neat n-dodecane injections. During mixing-controlled combustion phase apparent heat-release rate (aHRR) amplitudes increase for WFE with injection strategy (B) compared to the neat fuel sprays. At the gas temperature of 760 K non-sooting lifted flames have been detected for both fuels. Calculated fuel-to-air ratios Φ evaluated at the respective LOL agree well with soot occurrences for both fuels. Utilizing WFE, the additional latent heat introduced by the water increases LOLs and to a further extent the liquid fuel core which is found within the spray flame and therefore, a fuel rich combustion zone is suggested to surround the liquid-phase WFE. Hence, soot formation persists for calculated fuel-to-air ratios Φ<2 at the LOL, although, detected soot incandescence signals were on very low amplitude levels injecting the WFE.

Entropic Analysis of Mirror Symmetry Breaking in Chiral Hypercycles.

Replicators are fundamental to the origin of life and evolvability. Biology exhibits homochirality: only one of two enantiomers is used in proteins and nucleic acids. Thermodynamic studies of chemical replicators able to lead to homochirality shed valuable light on the origin of homochirality and life in conformity with the underlying mechanisms and constraints. In line with this framework, enantioselective hypercyclic replicators may lead to spontaneous mirror symmetry breaking (SMSB) without the need for additional heterochiral inhibition reactions, which can be an obstacle for the emergence of evolutionary selection properties. We analyze the entropy production of a two-replicator system subject to homochiral cross-catalysis which can undergo SMSB in an open-flow reactor. The entropy exchange with the environment is provided by the input and output matter flows, and is essential for balancing the entropy production at the non-equilibrium stationary states. The partial entropy contributions, associated with the individual elementary flux modes, as defined by stoichiometric network analysis (SNA), describe how the system’s internal currents evolve, maintaining the balance between entropy production and exchange, while minimizing the entropy production after the symmetry breaking transition. We validate the General Evolution Criterion, stating that the change in the chemical affinities proceeds in a way as to lower the value of the entropy production.

A Random Interrupt Dithering SAR Technique for Secure ADC Against Reference-Charge Side-Channel Attack

A side-channel attack (SCA) on a reference-charge flow in successive approximation register (SAR) analog-to-digital converters (ADCs) discloses analog information acquired at a sensor frontend. A random interrupt dithering masks the correlation between analog input and reference charge flow by injecting extremely large dither of 1/4 full scale. An internal dither-tracking comparator yet guarantees rail-to-rail operation, resulting in no penalty in conversion accuracy. The comparator functions as a physical-random source for dithering. The unpredictable randomness based on comparator metastable operation by thermal noise enhances the security level while the shared use of the comparator reduces the associated hardware overhead. The additional silicon area penalty for the proposed technique is only 7% of an unprotected ADC core area. A 10-bit 1 MS/s secure SAR ADC was fabricated in 0.18- $\mu \text{m}$ CMOS. The measurement results demonstrate the proposed secure ADC suppresses the information leakage from 4.6 bit to 0.8 bit against reference-charge SCA.

Integrated variable speed limit and ramp metering control study on flow interaction between mainline and ramps

During peak periods, bottlenecks are often triggered by excessive demand from both on-ramp and mainline input flows. To relieve bottleneck severity and improve traffic safety, ramp metering and variable speed limit are implemented to control the on-ramp and mainline input flows, and sometimes they are integrated. This article presents a proactive integrated control, with goals to save network-wide travel time and increase traffic flow. A METANET-based macroscopic traffic model was adopted as a prediction model. Micro-simulation tests were performed to evaluate and compare the control approaches among integrated and isolated control scenarios. By decoupling the traffic prediction and simulation models, the control error sources were analyzed. The evaluation revealed that both isolated and integrated controls benefit the traffic network to different extents under varying demand scenarios. Under proactive integrated control, ramp metering is activated solely during slight congestion; or it is activated during high-congestion periods to assist variable speed limit and thus integration maximizes the infrastructure utility.

Approaches to fill data gaps and evaluate process completeness in LCA—perspectives from solid waste management systems

Large data amounts are required in an LCA, but often, site-specific data are missing and less representative surrogate data must be used to fill data gaps. No standardized rules exist on how to address data gaps and process completeness. We suggest a systematic evaluation of process completeness, identification of data gaps, and application of surrogate values to fill the gaps. The study focus on foreground process data. A solid waste management (SWM) scenario was used to illustrate the suggested method. The expected input and output flows in a waste incineration model were identified based on legislation and expert judgment, after which process completeness scores were calculated and missing flows identified. To illustrate the use of different types of surrogate data to fill data gaps, data gaps were selected for 16 different parameters in five SWM processes. We compared the global warming potential (GWP) from using surrogate data, and from leaving the gap, to identify the data gaps where representative surrogate data should be used. The completeness score for the material inputs to waste incineration was 78%, and the missing flows were auxiliary fuels and precipitation chemicals. The completeness score for air emissions were between 38 and 50% with and without expert judgment. If only greenhouse gases were considered (CO2, CH4, and N2O), the completeness score would be 67%. Applying weighting factors according to the greenhouse gas contribution in the USA gave a completeness score of 94%. The system-wide data gaps, where representative surrogate data should be applied, were the CH4 release from composting; electricity generation efficiency of incineration; recovery efficiencies at a material recovery facility; and composition of the plastic, metal, and paper fractions in the household waste; in these cases, leaving the gap changed the GWP results by > 5%. Completeness evaluation should take into account the relevance and importance of flows; relevance depends on the considered life cycle impact methods and importance depends on the weighting of the different flows. The set of expected flows and evaluation of relevance and importance must be documented in a transparent manner. The choice of surrogate values to fill data gaps depends on the availability of secondary data and on whether the data gap matters, i.e., significantly affects the LCA results. The suggested method can be used to properly document the identification of missing flows and to select and apply surrogate values to fill the data gaps.

Sensitivity of Life-Cycle Assessment Outcomes to Parameter Uncertainty: Implications for Material Procurement Decision-Making

This paper aims to apply an analytical approach to propagate parameter uncertainty through Life-Cycle Assessment (LCA) outcomes, and identify equivalence intervals that are applicable during material procurement decision-making. LCA outputs are usually presented as point estimates without accompanying confidence intervals, or associated margins of error, due to methodological ambiguity in accounting for uncertainties, be they epistemic (due to inherent randomness) or aleatory (due to lack of knowledge). This reduces the reliability of using LCA for design selection, and of decision-making during material procurement. This paper aims to fill this gap using a methodology based on Taylor’s first-order approximation to examine LCA outcomes for asphalt mixtures. The method is applied to assess the impact of variation in input flows on the estimated output emissions by propagating the parameter uncertainties through the LCA. It allows for the reporting of LCA outputs using intervals rather than point estimates. For competing designs, the overlap in intervals is used to construct equivalence intervals within which the effective impact of the designs can be considered equivalent due to expected variability in input parameters. The method is applied to construct equivalence intervals for the Global Warming Potential (GWP) of three asphalt mixtures, each having different levels of Reclaimed Asphalt Pavement (RAP). Their role in communicating LCA outcomes for decision-making is illustrated. Foreground data collected from 40 North American asphalt plants were used to estimate uncertainty in the input parameters of electricity and energy use in asphalt production. The paper adds to existing literature on uncertainties in pavement LCAs by establishing the need to incorporate uncertainty when using LCA to support decision-making during material procurement.