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International audience; Volatile fatty acids (VFA), inorganic carbon (IC) and total ammonia nitrogen (TAN) are key variables in the current context of anaerobic digestion (AD). Accurate measurements like gas chromatography and infrared spectrometry have been developed to follow the concentration of these compounds but none of these methods are affordable for small AD units. Only titration methods answer the need for small plant monitoring. The existing methods accuracy was assessed in this study and reveals a lack of accuracy and robustness to control AD plants. To solve these issues, a new titrimetric device to estimate the VFA, IC and TAN concentrations with an improved accuracy was developed. This device named SNAC (System of titration for total ammonia Nitrogen, volatile fatty Acids and inorganic Carbon) has been developed combining the measurement of electrical conductivity and pH. SNAC were tested on 24 different plant samples in a range of 0–0.16 mol.L−1 TAN, 0.01–0.21 mol.L−1 IC and 0–0.04 mol.L−1 VFA. The standard error was about 0.012 mol.L−1 TAN, 0.015 mol.L−1 IC and 0.003 mol.L−1 VFA. The coefficient of determination R2 between the estimated and reference data was 0.95, 0.94 and 0.95 for TAN, IC and VFA respectively. Using the same data, current methods based on key pH points lead to standard error more than 14.5 times higher on VFA and more than 1.2 times higher on IC. These results show that SNAC is an accurate tool to improve the management of AD plant.

International audience; The growing need to use biofuel raw materials that do not compete with food and feed have resulted in a growing interest in lignocellulosic materials and microalgae. However, the life cycle environmental benefits of both biofuels have been questioned. The aim of this study was to evaluate how environmental sustainability of forest-based and microalgae biodiesel can be estimated by using the life cycle assessment framework. These biofuel chains were chosen because they are contrasting systems, as the first one is based on a “natural” feedstock production system, while the second one is an entirely anthropogenic system using an artificial infrastructure and external inputs to grow microalgae. This study focuses on life cycle impact categories still under methodological development, namely resource depletion, land use and land use change, water use, soil quality impacts and biodiversity. In addition, climate impacts were quantified in order to exemplify the uncertainty of the results and the complexity of estimating the parameters. This study demonstrates the difficulty to assess the absolute range of the total environmental impacts of the two systems. The results propose that the greenhouse gas emissions of microalgae biodiesel are higher than those of forest residue-based biodiesel, but the results of the microalgae chain are very uncertain due to the early development stage of the technology, and due to assumptions made concerning the electricity mix. On the other hand, the microalgae system has other advantages such as low competition on productive land and low biodiversity impacts. The findings help to recognise the main characteristics of the two production chains, and the main remaining research issues on bioenergy assessment along with the methodological development needs of life cycle approaches.; Le besoin croissant d'utiliser des matières premières de biocarburants qui n'entrent pas en compétition avec la nourriture et les aliments ont entraîné un intérêt croissant pour les matériaux lignocellulosiques et microalgues. Cependant, le cycle de vie des avantages environnementaux des biocarburants deux ont été interrogés. Le but de cette étude était d'évaluer comment la durabilité environnementale de biodiesel à base de forêt et microalgues peut être estimée en utilisant le cadre d'évaluation du cycle de vie. Ces filières de biocarburants ont été choisis parce qu'ils sont les systèmes contrastés, que le premier est basé sur un système de production de matières premières "naturel", tandis que le second est un système entièrement anthropique utilisant une infrastructure artificielle et des apports extérieurs pour se développer microalgues. Cette étude se concentre sur les catégories d'impacts du cycle de vie en cours de développement méthodologique, à savoir l'épuisement des ressources, l'utilisation des terres et les changements d'utilisation des terres, l'utilisation de l'eau, les impacts sur la qualité des sols et de la biodiversité. En outre, les effets du changement climatique ont été quantifiés de manière à illustrer l'incertitude des résultats et de la complexité de l'estimation des paramètres. Cette étude démontre la difficulté d'évaluer la portée absolue des impacts environnementaux globaux des deux systèmes. Les résultats suggèrent que les émissions de GES de biodiesel de microalgues sont plus élevés que ceux du biodiesel à base de résidus forestiers, mais les résultats de la chaîne de microalgues sont très incertaines en raison du stade de développement précoce de la technologie, et en raison des hypothèses retenues concernant l'électricité mélanger. D'autre part, le système de microalgues a d'autres avantages tels que la faible concurrence sur les terres productives et son faible impact sur la biodiversité. Les résultats aident à reconnaître les principales caractéristiques des deux chaînes de production, et les principales questions de recherche restant sur l'évaluation de la bioénergie ainsi que les besoins de développement méthodologique des approches du cycle de vie.

International audience; Due to resource depletion and climate change, lipid-based algal biofuel has been pointed out as an interesting alternative because of the high productivity of algae per hectare and per year and its ability to recycle CO2 from flue gas. Another option for taking advantage of the energy content of the microalgae is to directly carry out anaerobic digestion of raw algae in order to produce methane and recycle nutrients (N, P and K). In this study, a life-cycle assessment (LCA) of biogas production from the microalgae Chlorella vulgaris is performed and the results are compared to algal biodiesel and to first generation biodiesels. These results suggest that the impacts generated by the production of methane from microalgae are strongly correlated with the electric consumption. Progresses can be achieved by decreasing the mixing costs and circulation between different production steps, or by improving the efficiency of the anaerobic process under controlled conditions. This new bioenergy generating process strongly competes with others biofuel productions.

LCAs (life cycle assessments) are often based on average data to produce a generic evaluation of a good or service. However, ignoring variability and induced uncertainty of LCA results reduces their significance, especially when dealing with agricultural processes that present high natural fluctuations. The objective of the study was to explore the robustness of LCA results when accounting for variable emissions data, illustrated by the case of slurry application techniques. Four application techniques were compared: band spreading, broadcast spreading, harrowing after surface application and direct injection. On the basis of the normalisation results, acidification, eutrophication and global warming potentials were selected. To estimate field nitrogen emissions, an original approach was developed based on relative nitrogen loss factors for each technique from a literature review. The calculated field emissions from different soil and climate conditions were considered equally probable and were propagated into a range of LCA result using the Monte Carlo method. Injection and harrowing both showed reduced acidification and eutrophication potentials compared to band spreading and broadcast spreading but had larger global warming potentials, which could be particularly important with injection. Harrowing consequently appeared as the best compromise. Despite the large range of LCA results, robust conclusions could be drawn. To achieve a more refined comparison between the techniques, the use of process-based models in contrasted situations is suggested.

The on-line diagnosis is a key requirement in biological processes. This is particularly true in the case of wastewater treatment processes due to the composition of media, the requirements of operating conditions and the wide variety of possible disturbances that necessitate careful and constant monitoring of the processes. Moreover, because only partial information is available in an online context and because of the technical and biological complexities of the involved processes, specific characteristics are required for diagnosis purposes. Several approaches like quantitative model based, qualitative model based and process history based methods were applied over the years. This paper present a methodological framework based on evidence theory to manage the fault signals generated by conventional approaches (i.e., residuals from hardware and software redundancies, fuzzy logic based modules for process state assessment) and to account for uncertainty. The advantages of using evidence theory like modularity, detection of conflict and doubt in the information sources are illustrated with experimental results from a 1 m 3 fixed bed anaerobic digestion process used for the treatment of industrial distillery wastewater.