arnaud Hélias - Academia.edu (original) (raw)
Papers by arnaud Hélias
L'essor de l'elevage intensif sur l'ile de la Reunion a induit une forte production d... more L'essor de l'elevage intensif sur l'ile de la Reunion a induit une forte production d'effluents qui ne peut plus etre negligee face aux contraintes environnementales et reglementaires. Modeliser les actions d'epandage, leurs causes et consequences, apparait alors comme un point de pour tester des scenarios de gestion des effluents d'elevage. Cet article porte sur la representation dynamique d'un reseau de producteurs (i.e., les elevages) et de consommateurs (i.e., les cultures) d'effluents. II nous faut pour cela confronter des dynamiques de stocks imprecises (considerees comme continues) avec des modeles discrets de representation des actions. Notre approche est basee sur une modelisation par le formalisme des automates temporises et la definition d'une procedure, automatisee et generique, d'approximation des modeles continus, avec prise en compte d'imprecisions sur leurs etats initiaux et variables d'entree. Pour chacune des unites (...
During the cheese ripening, airflow pattern and climatic conditions inside cheese-ripening rooms ... more During the cheese ripening, airflow pattern and climatic conditions inside cheese-ripening rooms are determinant for cheese weight losses. Due to the variation of air velocity inside ripening chambers, homogeneity in the distribution of climatic conditions is very hard to achieve at every single point of it. We are hence faced with imprecise and incomplete knowledge. In practice, it is common that some model parameters may be represented by single probability distributions, justified by substantial data, while others are more faithfully represented by possibility distributions due to the partial nature of available knowledge. This paper applies recent methods, designed for the joint propagation of variability and imprecision, to a cheese ripening mass loss model. Joint propagation methods provide lower & upper probability bounds of exceeding a certain value of cheese mass losses.
ABSTRACT Fossil fuel depletion and climate change have lead many research groups and private comp... more ABSTRACT Fossil fuel depletion and climate change have lead many research groups and private companies to focus on use of biomass to produce renewable energy and fuel. Because of their high production yield, micro-algae have been pointed as an interesting alternative. A relevant mean to upgrade the energy value of micro-algae with optimal performances is the anaerobic digestion of the algae. It enables achievement of environmental benefits and production of energy from renewable resources. However such processes only exist at lab-scale. In order to assess and optimize its performances and environmental impacts, one has to stimulate its behaviour through dynamical models. In broad outline the two major compartments of the system (micro-algae culture and anaerobic digestion process) are linked by internal flows (micro-algae, digestatesldots) and receive external flows (light, cosubstratesldots). As a consequence, overall behaviour is determined by the interaction of several time-dependent processes. For example, the temporal availability of winery effluents induces a better anaerobic digestion due to the high C/N ratio of this kind of cosubstrate, and consequently a bigger production of biogas. So, due to the close loop operating, the needs of chemical fertilizers are lower, and the emissions caused by their production too. This shows the necessity to realize a dynamic Life Cycle Assessment. In our context, a pertinent Life Cycle Inventory can not be achieved without taking into account the dynamic of several processes; some economic flows are determined according to the temporal evolution of processes. Consequently, we integrate dynamic system modeling of micro-algae growth and anaerobic digestion of biomass in the LCA in order to obtain dynamic flows. This approach allows us to obtain dynamic data for the Life Cycle Inventory. This is a preliminary step to more accurate impact assessment.
Because of intensive animal farming, the problem of animal wastes disposal has become very acute ... more Because of intensive animal farming, the problem of animal wastes disposal has become very acute in the Reunion Island, namely for liquid wastes such as pig slurry. In this paper we address the problem of determining efficient supply policies of a slurry treatment plant collectively managed by individual farmers. For this, we built a simulation model with a continuous part (i.e., slurry stocks modeled as ordinary differential equations) and a discrete part (i.e., transport allocation as a Linear Program). Simulations are carried out considering the specific constraints of farmers in a critical zone in the Reunion Island. The results emphasize the positive role of a closed-loop control, which means organizing slurry transportation according to the current states of individual stocks. (Resume d'auteur)
Langlois et al. (2012; 2014a) proposed characterization factors (CF) for fish biotic resource ext... more Langlois et al. (2012; 2014a) proposed characterization factors (CF) for fish biotic resource extraction impact assessment at the species level. This paper is an improvement of this approach. In the present work, the CF depends on the Maximum Sustainability Yield (MSY), weighted by the ratio of the current total fishing effort to the fishing effort at the MSY value. Because this ratio often cannot be computed from current databases, it is here obtained from the ratio of total catches to MSY and roots of the parabola linking catches to fishing effort. The new version of the CF is proposed for 125 fish stocks. This work allows assessment of fisheries in the LCA formalism. It contributes to a better representation of the depletion of biotic resources.
L'essor de l'elevage intensif, notamment a l'ile de la Reunion, induit une forte prod... more L'essor de l'elevage intensif, notamment a l'ile de la Reunion, induit une forte production d'effluents qui ne peut plus etre negligee face aux contraintes environnementales et reglementaires associees. Modeliser les decisions d'epandage, leurs causes et consequences apparaissent alors comme des points cles pour tester des scenarios de gestion des effluents d'elevages. Cette these porte sur la representation dynamique d'un reseau de producteurs (i. E. , les elevages) et de consommateurs (i. E. , les cultures) d'effluents. Il faut alors confronter des dynamiques de stocks imprecises avec des modeles discrets de prise de decision. Notre approche est (i) une modelisation par le formalisme des automates temporise accompagnee de (ii) la definition d'une procedure, automatisee et generique, d'approximation des modeles continus, avec prise en compte d'imprecisions SUl les etats initiaux et les variables d'entree. L'approche de discretisat...
Postharvest Biology and Technology
Science of The Total Environment
Low carbon strategies recently focus on soil organic carbon (SOC) sequestration potentials from a... more Low carbon strategies recently focus on soil organic carbon (SOC) sequestration potentials from agriculture and forestry, while Life Cycle Assessment (LCA) increasingly becomes the framework of choice to estimate the environmental impacts of these activities. Classic LCA is limited to static carbon neutral approaches, disregarding dynamic SOC flows and their time-dependent GHG contributions. To overcome such limitation, the purpose of this study is to model SOC flows associated with agricultural land use (LU) and the provision of agricultural substrates to transport biofuels, thus generating dynamic inventories and comparatively assessing energy policy scenarios and their climate consequences in the context of dynamic LCA. The proposed framework allows computing SOC from annual and perennial species under specific management practices (e.g. residue removal rates, organic fertiliser use). The results associated with the implementation of three energy policies and two accounting philosophies (C-neutral and C-complete) show that shifting energy pathways towards advanced biofuels reduces overall resource consumption, LU and GHG emissions. The French 2015 Energy Transition for Green Growth Act (LTECV) leads towards higher mitigation targets compared with business-as-usual (BAU) and intermediate (15BIO) policy constraints. C-neutral results show reduced radiative forcing effects by 10% and 34% for 15BIO and LTECV respectively, with respect to BAU. C-complete (i.e. dynamic assessment of all biogenic- and fossil-sourced C flows) results reveal further mitigation potentials across policies, whereof 50%-65% can be attributed to temporal C sequestration in perennial rhizomes. A sensitivity analysis suggests important SOC variations due to temperature increase (+2°C) and changes in residue removal rates. Both parameters affect mitigation and the latter also LU, by a factor of -0.56 to + 5. This article highlights the importance of SOC modelling in the context of LU in LCA, which is usually disregarded, as SOC is considered only in the context of land use change (LUC).
Data
Assessing the state of fish stocks requires the determination of descriptors. They correspond to ... more Assessing the state of fish stocks requires the determination of descriptors. They correspond to the absolute and relative (to the carrying capacity of the habitat) fish biomasses in the ecosystem, and the absolute and relative (to the intrinsic growth rate of the population) fishing mortality resulting from catches. This allows, among other things, to compare the catch with the maximum sustainability yield. Some fish stocks are well described and monitored, but for many data-limited stocks, catch time series are remaining the only source of data. Recently, an algorithm (CMSY) has been proposed, allowing an estimation of stock assessment variables from catch and resilience. In this paper, we provide stock reference points for all global fisheries reported by Food and Agriculture Organization (FAO) major fishing area for almost 5000 fish stocks. These data come from the CMSY algorithm for 42% of the stock (75% of the global reported fish catch) and are estimated by aggregated values ...
The International Journal of Life Cycle Assessment
Resources, Conservation and Recycling
Science of The Total Environment
Agronomy for Sustainable Development
Sciences Eaux & Territoires
Science of The Total Environment
Science of The Total Environment
The International Journal of Life Cycle Assessment
Biotechnology for Biofuels
Background Microalgae are 10 to 20 times more productive than the current agricultural biodiesel ... more Background Microalgae are 10 to 20 times more productive than the current agricultural biodiesel producing oleaginous crops. However, they require larger energy supplies, so that their environmental impacts remain uncertain, as illustrated by the contradictory results in the literature. Besides, solar radiation is often too high relative to the photosynthetic capacity of microalgae. This leads to photosaturation, photoinhibition, overheating and eventually induces mortality. Shadowing microalgae with solar panels would, therefore, be a promising solution for both increasing productivity during hotter periods and producing local electricity for the process. The main objective of this study is to measure, via LCA framework, the energy performance and environmental impact of microalgae biodiesel produced in a solar greenhouse, alternating optimal microalgae species and photovoltaic panel (PV) coverage. A mathematical model is simulated to investigate the microalgae productivity in race...
L'essor de l'elevage intensif sur l'ile de la Reunion a induit une forte production d... more L'essor de l'elevage intensif sur l'ile de la Reunion a induit une forte production d'effluents qui ne peut plus etre negligee face aux contraintes environnementales et reglementaires. Modeliser les actions d'epandage, leurs causes et consequences, apparait alors comme un point de pour tester des scenarios de gestion des effluents d'elevage. Cet article porte sur la representation dynamique d'un reseau de producteurs (i.e., les elevages) et de consommateurs (i.e., les cultures) d'effluents. II nous faut pour cela confronter des dynamiques de stocks imprecises (considerees comme continues) avec des modeles discrets de representation des actions. Notre approche est basee sur une modelisation par le formalisme des automates temporises et la definition d'une procedure, automatisee et generique, d'approximation des modeles continus, avec prise en compte d'imprecisions sur leurs etats initiaux et variables d'entree. Pour chacune des unites (...
During the cheese ripening, airflow pattern and climatic conditions inside cheese-ripening rooms ... more During the cheese ripening, airflow pattern and climatic conditions inside cheese-ripening rooms are determinant for cheese weight losses. Due to the variation of air velocity inside ripening chambers, homogeneity in the distribution of climatic conditions is very hard to achieve at every single point of it. We are hence faced with imprecise and incomplete knowledge. In practice, it is common that some model parameters may be represented by single probability distributions, justified by substantial data, while others are more faithfully represented by possibility distributions due to the partial nature of available knowledge. This paper applies recent methods, designed for the joint propagation of variability and imprecision, to a cheese ripening mass loss model. Joint propagation methods provide lower & upper probability bounds of exceeding a certain value of cheese mass losses.
ABSTRACT Fossil fuel depletion and climate change have lead many research groups and private comp... more ABSTRACT Fossil fuel depletion and climate change have lead many research groups and private companies to focus on use of biomass to produce renewable energy and fuel. Because of their high production yield, micro-algae have been pointed as an interesting alternative. A relevant mean to upgrade the energy value of micro-algae with optimal performances is the anaerobic digestion of the algae. It enables achievement of environmental benefits and production of energy from renewable resources. However such processes only exist at lab-scale. In order to assess and optimize its performances and environmental impacts, one has to stimulate its behaviour through dynamical models. In broad outline the two major compartments of the system (micro-algae culture and anaerobic digestion process) are linked by internal flows (micro-algae, digestatesldots) and receive external flows (light, cosubstratesldots). As a consequence, overall behaviour is determined by the interaction of several time-dependent processes. For example, the temporal availability of winery effluents induces a better anaerobic digestion due to the high C/N ratio of this kind of cosubstrate, and consequently a bigger production of biogas. So, due to the close loop operating, the needs of chemical fertilizers are lower, and the emissions caused by their production too. This shows the necessity to realize a dynamic Life Cycle Assessment. In our context, a pertinent Life Cycle Inventory can not be achieved without taking into account the dynamic of several processes; some economic flows are determined according to the temporal evolution of processes. Consequently, we integrate dynamic system modeling of micro-algae growth and anaerobic digestion of biomass in the LCA in order to obtain dynamic flows. This approach allows us to obtain dynamic data for the Life Cycle Inventory. This is a preliminary step to more accurate impact assessment.
Because of intensive animal farming, the problem of animal wastes disposal has become very acute ... more Because of intensive animal farming, the problem of animal wastes disposal has become very acute in the Reunion Island, namely for liquid wastes such as pig slurry. In this paper we address the problem of determining efficient supply policies of a slurry treatment plant collectively managed by individual farmers. For this, we built a simulation model with a continuous part (i.e., slurry stocks modeled as ordinary differential equations) and a discrete part (i.e., transport allocation as a Linear Program). Simulations are carried out considering the specific constraints of farmers in a critical zone in the Reunion Island. The results emphasize the positive role of a closed-loop control, which means organizing slurry transportation according to the current states of individual stocks. (Resume d'auteur)
Langlois et al. (2012; 2014a) proposed characterization factors (CF) for fish biotic resource ext... more Langlois et al. (2012; 2014a) proposed characterization factors (CF) for fish biotic resource extraction impact assessment at the species level. This paper is an improvement of this approach. In the present work, the CF depends on the Maximum Sustainability Yield (MSY), weighted by the ratio of the current total fishing effort to the fishing effort at the MSY value. Because this ratio often cannot be computed from current databases, it is here obtained from the ratio of total catches to MSY and roots of the parabola linking catches to fishing effort. The new version of the CF is proposed for 125 fish stocks. This work allows assessment of fisheries in the LCA formalism. It contributes to a better representation of the depletion of biotic resources.
L'essor de l'elevage intensif, notamment a l'ile de la Reunion, induit une forte prod... more L'essor de l'elevage intensif, notamment a l'ile de la Reunion, induit une forte production d'effluents qui ne peut plus etre negligee face aux contraintes environnementales et reglementaires associees. Modeliser les decisions d'epandage, leurs causes et consequences apparaissent alors comme des points cles pour tester des scenarios de gestion des effluents d'elevages. Cette these porte sur la representation dynamique d'un reseau de producteurs (i. E. , les elevages) et de consommateurs (i. E. , les cultures) d'effluents. Il faut alors confronter des dynamiques de stocks imprecises avec des modeles discrets de prise de decision. Notre approche est (i) une modelisation par le formalisme des automates temporise accompagnee de (ii) la definition d'une procedure, automatisee et generique, d'approximation des modeles continus, avec prise en compte d'imprecisions SUl les etats initiaux et les variables d'entree. L'approche de discretisat...
Postharvest Biology and Technology
Science of The Total Environment
Low carbon strategies recently focus on soil organic carbon (SOC) sequestration potentials from a... more Low carbon strategies recently focus on soil organic carbon (SOC) sequestration potentials from agriculture and forestry, while Life Cycle Assessment (LCA) increasingly becomes the framework of choice to estimate the environmental impacts of these activities. Classic LCA is limited to static carbon neutral approaches, disregarding dynamic SOC flows and their time-dependent GHG contributions. To overcome such limitation, the purpose of this study is to model SOC flows associated with agricultural land use (LU) and the provision of agricultural substrates to transport biofuels, thus generating dynamic inventories and comparatively assessing energy policy scenarios and their climate consequences in the context of dynamic LCA. The proposed framework allows computing SOC from annual and perennial species under specific management practices (e.g. residue removal rates, organic fertiliser use). The results associated with the implementation of three energy policies and two accounting philosophies (C-neutral and C-complete) show that shifting energy pathways towards advanced biofuels reduces overall resource consumption, LU and GHG emissions. The French 2015 Energy Transition for Green Growth Act (LTECV) leads towards higher mitigation targets compared with business-as-usual (BAU) and intermediate (15BIO) policy constraints. C-neutral results show reduced radiative forcing effects by 10% and 34% for 15BIO and LTECV respectively, with respect to BAU. C-complete (i.e. dynamic assessment of all biogenic- and fossil-sourced C flows) results reveal further mitigation potentials across policies, whereof 50%-65% can be attributed to temporal C sequestration in perennial rhizomes. A sensitivity analysis suggests important SOC variations due to temperature increase (+2°C) and changes in residue removal rates. Both parameters affect mitigation and the latter also LU, by a factor of -0.56 to + 5. This article highlights the importance of SOC modelling in the context of LU in LCA, which is usually disregarded, as SOC is considered only in the context of land use change (LUC).
Data
Assessing the state of fish stocks requires the determination of descriptors. They correspond to ... more Assessing the state of fish stocks requires the determination of descriptors. They correspond to the absolute and relative (to the carrying capacity of the habitat) fish biomasses in the ecosystem, and the absolute and relative (to the intrinsic growth rate of the population) fishing mortality resulting from catches. This allows, among other things, to compare the catch with the maximum sustainability yield. Some fish stocks are well described and monitored, but for many data-limited stocks, catch time series are remaining the only source of data. Recently, an algorithm (CMSY) has been proposed, allowing an estimation of stock assessment variables from catch and resilience. In this paper, we provide stock reference points for all global fisheries reported by Food and Agriculture Organization (FAO) major fishing area for almost 5000 fish stocks. These data come from the CMSY algorithm for 42% of the stock (75% of the global reported fish catch) and are estimated by aggregated values ...
The International Journal of Life Cycle Assessment
Resources, Conservation and Recycling
Science of The Total Environment
Agronomy for Sustainable Development
Sciences Eaux & Territoires
Science of The Total Environment
Science of The Total Environment
The International Journal of Life Cycle Assessment
Biotechnology for Biofuels
Background Microalgae are 10 to 20 times more productive than the current agricultural biodiesel ... more Background Microalgae are 10 to 20 times more productive than the current agricultural biodiesel producing oleaginous crops. However, they require larger energy supplies, so that their environmental impacts remain uncertain, as illustrated by the contradictory results in the literature. Besides, solar radiation is often too high relative to the photosynthetic capacity of microalgae. This leads to photosaturation, photoinhibition, overheating and eventually induces mortality. Shadowing microalgae with solar panels would, therefore, be a promising solution for both increasing productivity during hotter periods and producing local electricity for the process. The main objective of this study is to measure, via LCA framework, the energy performance and environmental impact of microalgae biodiesel produced in a solar greenhouse, alternating optimal microalgae species and photovoltaic panel (PV) coverage. A mathematical model is simulated to investigate the microalgae productivity in race...