: éditorial

International audienc

Toward the Valorization of Waste and Biomass

International audienceValorization is the conversion of waste and biomass to energy, fuels and other useful materials, with particular focus on environmental indicators and sustainability goals. It is part of the larger endeavor of loop-closing. This topic is the object of cooperation between a large number of actors from various fields of engineering sciences, health and safety. In this paper, the relevance and the interest in this topic is discussed and supported with examples. The two examples proposed concern biomass and plastic films. Biomass has gained a tremendous interest during the ten last years and will be a subject for significant research progress in the future. The evolution of research in the production of biofuels from first, second and third generation biomass is discussed using thermal process. The second example concerns plastic films; valorization of plastics has been investigated for two decades already with relevant progress. However, this paper shows that there are still a number of issues to tackle and overcome for an efficient and effective valorization of plastic films. To improve and reach a significant valorization, integrated processes for proper separation, detection and classification of plastic film from industrial and commercial packaging waste are discussed. The paper also highlights the bottlenecks, barriers and challenging issues such as the emission of pollutants and greenhouse gases, energy efficiency, modeling, characterization, regulation and policy that will drive the development of this field in the future

Agglomeration of Metals During Pyrolysis of Chromated Copper Arsenate (CCA) Treated Wood Waste

Issu de : WasteEng 2008, Patras, GREECE, 3-5 June 2008International audienceThe number of waste disposal sites decreases and redundant poles, piling and lumber, which constitute a large volume of material, may not be accepted at the limited number of sites in the future. CCA contaminated wood contains around 1-5% of metal in form of arsenic pentoxide, hexavalent and trivalent chromium compounds and copper sulfate, which act as fungicides and insecticides throughout the life of the wood. While CCA treatment is gradually becoming a banned practice, approximately 4 million tonnes of CCA treated wood is generated in the EU per year, which is set to continue for many decades as the in-service wood is generated in end of its life. Recycling wood waste is important for the effective utilization of natural resources. The charcoal product resulting from CCA treated wood contains Cu, Cr and As. The metals appear as both agglomerates and diffused in the solid matrix. Moreover, during pyrolysis an agglomeration process takes place, which induces not only the growth of existing mineral agglomerates but also the formation of new agglomerates. The objective of the present work is the valorisation of CCA metals and charcoal from treated wood waste. The research aims at understanding and promoting experimentally, at different pyrolysis heating rates, the generation of charcoal with high specific surface area from pyrolysed treated wood waste

: Préface

International audienc

Stabilization of minerals by reaction with phosphoric acid - Evolution of model compounds

International audienceThe mechanisms of heavy metal stabilization from mineral residues were investigated. The reaction of phosphoric acid with municipal waste incinerator fly ashes and some of its major constituents was assessed. The reaction was monitored by analysis of soluble phosphate contents as a function of time, as well as by pH and temperature variations. Evolution of the solids was followed by X-ray diffraction. Various phosphoric acid concentrations were used and yielded different end products for the case of little and limestone. Silica and calcium sulphate were found to remain inert, while alumina consumed part of the soluble phosphate. Melilite showed it complex process of dissolution and precipitation of amorphous aluminium phosphates. These results help on understanding the phosphate reaction used to stabilize a mineral matrix like fly ash and demonstrate that insoluble minerals are formed such as calcium phosphates which may effectively trap heavy metal ions

Alum sludge as an efficient sorbent for hydrogen sulfide removal: Experimental, mechanisms and modeling studies

International audienceThis paper firstly reported a systematic study of using alum sludge (waterworks residue) for H2S adsorption. Various trials were performed at ambient temperature in a fixed bed column to study the effects of H2S flow rate, sorbent bed depth on the alum sludge adsorption efficiency of H2S. The Breakthrough Curves were simulated by the Thomas model, Bed Depth Service Time model and Yoon-Nelson models. The mechanisms of H2S adsorption onto alum sludge was examined by different physiochemical characterizations of exhausted and raw alum sludge. Moreover, the mass transfer coefficients were determined from mathematical descriptions of breakthrough curves. The alum sludge adsorption capacity was determined to be 374.2 mg of H2S/g, slightly decreasing with the increasing flow rate and increasing with the increasing bed depth. All the three models successfully predict breakthrough curves which could be used for scaling-up purposes. The microporous structure, alkaline pH and the inherent metal species of the alum sludge promoted the formation of metal sulphate species. This study demonstrated that alum sludge could be used as cost-effective, largely available, and efficient sorbent for H2S removal

Key factors influencing the environmental performance of pyrolysis, gasification and incineration Waste-to-Energy technologies

International audienceWaste-to-Energy (WtE) has started playing an increasingly important role in the recovery of energy from municipal solid waste (MSW). A number of WtE technologies are being developed. However, selecting a more environmentally sustainable option is difficult due to data limitation and methodological inconsistencies. Using life cycle assessment (LCA) as a tool, this paper aims to identify key factors influencing the potential environmental impacts of four representative WtE technologies, namely the incineration (S1), pyrolysis (S2), gasification (S3), and gasification coupled with ash melting (S4). The systems are constructed using inventory data based on on-site operation of several industrial-scale reference plants. A comprehensive sensitivity analysis is conducted, assessing a range of critical input parameters, processes, operating conditions and modelling assumptions. The results demonstrate that all analysed WtE systems exhibit environmental benefits (i.e. negative environmental impacts) for most of the impacts, while S3 seems to be more optimal due to an intermediate syngas cleaning process, which results in both reduced emissions and increased energy recovery. Parameters driving the environmental impacts are energy recovery efficiency, feedstock variability, NOx and CO2 emissions at stack, and recycling of metals. Moreover, the overall ranking of different WtE systems is strongly dependent on operating conditions, such as effectiveness of the air pollution control process, utilization pathway of pyrolysis char, and to a lesser extent, bottom ash management (landfill or recycling). The LCA modelling conditions, such as substituted source of electricity, choice of functional unit and time frame are also shown to significantly affect the quantified environmental performance. Finally, the study highlights the directions, towards which, efforts should be focused throughout all stages of each WtE technology to obtain further improvements

Stabilisation of heavy metal containing dusts by reaction with phosphoric acid: study of the reactivity of fly ash

International audienceWater-washed fly ash was reacted with phosphoric acid in order to transform available heavy metals into insoluble metal phosphate compounds. The temperature, pH and concentration of free phosphate were monitored during the first 80 min of reaction. Phosphoric acid reacted rapidly with second order kinetics and an apparent rate constant of 0.015 l/(mol s m(2)). Analysis of the evolution of the concentrations of other major elements of fly ash shows that the reaction follows a dissolution-precipitation type mechanism. The solubility of trace heavy metals tends to increase at low pH values. Various heat and mass transfer coefficients are derived and help understand the phosphate stabilisation procedure and design industrial reactors for this purpose. Calcium phosphates are formed which can trap heavy metals in a stable apatite mineral structure

Study the Nature and the Effects of the Impurities of Phosphate Rock in the Plants of Production of Phosphoric Acid

Phosphate rocks from different deposits vary widely in composition, and these variations have important effects in phosphoric acid production. All phosphate rocks contain many impurities. Knowledge of the nature and contents of the various elements in the phosphate is required in the manufacturing process of phosphoric acid. All these chemical characteristics can help the operator to foresee its objectives under the operating conditions and the cost of production in the manufacturing process of phosphoric acid.Two Tunisian natural phosphates coming from two different deposits were selected. We propose in this work studying the effects of the impurities that depending on their concentration can affect decisively the behavior of these ores in the process of production of phosphoric acid. Study the chemical composition of these ores is carried out according to standard analytical methods used for raw phosphates.The results obtained show a slight difference in chemical properties between the two types of sedimentary phosphates and their aptitude to be used in the plants of production of phosphoric acid.Â

Accumulators for the Capture of Heavy Metals in Thermal Conversion Systems

International audienceA clay ceramic with organic additives (biomass and biochar) was investigated for the development of highly porous accumulators to capture heavy metals in thermal conversion systems. The structure was characterized using X-ray pair distribution function analysis, differential scanning calorimetry, and scanning electron microscopy. It was found that the organic additives transformed into porosity during firing. The morphology of the pores also corresponded to the morphology of the organic additives. Hence, the clay ceramic with a 15-wt% addition of biochar had a porosity of 46 vol% with 20-μm interconnected pores after firing. The resulting accumulator was found to capture cadmium (a model for heavy metals with high volatility) via condensation of the cadmium vapor as 2-μm beads in the pores. The cadmium capture efficiency reached up to 57% using a 15-wt% addition of biochar. Furthermore, cadmium was captured at higher temperatures than the condensation temperature in the atmosphere. This means that heavy metals may be captured before they condense in fly ash to promote the recycling of this material