Energy recovery from wet biomass and waste

Certaines catégories de déchets organiques comme les boues, certains déchets agricoles ou des industries agro-alimentaires sont généralement considérés comme peu compatibles avec une utilisation en tant que combustibles solides en raison de leur forte teneur en eau. Cet article examine les concepts étudiés au cours de la dernière décennie, pour améliorer le bilan énergétique d'une filière basée sur la production de combustibles solides à vocation industrielle. Il démontre l'importance de l'efficacité énergétique de la déshydratation et du séchage pour assurer une réelle substitution des combustibles fossiles

Heat and mass transfer during fry-drying of sewage sludge

Deep-frying, which consists of immersing a wet material in a large volume of hot oil, presents a process easily adaptable to dry rather than cook materials. A suitable material for drying is sewage sludge, which may be dried using recycled cooking oils (RCO) as frying oil. One advantage is that this prepares both materials for convenient disposal by incineration. This study examines fry-drying of municipal sewage sludge using recycled cooking oil. The transport processes occurring during fry-drying were monitored through sample weight, temperature, and image analysis. Due to the thicker and wetter samples than the common fried foods, high residual moisture is observed in the sludge when the boiling front has reached the geometric center of the sample, suggesting that the operation is heat transfer controlled only during the first half of the process followed by the addition of other mechanisms that allow complete drying of the sample. A series of mechanisms comprising four stages (i.e., initial heating accompanied by a surface boiling onset, film vapor regime, transitional nucleate boiling, and bound water removal) is proposed. In order to study the effect of the operating conditions on the fry-drying kinetics, different oil temperatures (from 120 to 180 degrees C), diameter (D = 15 to 25 mm), and initial moisture content of the sample (4.8 and 5.6 kg water(.)kg(-1) total dry solids) were investigated

The environmental performance of an alternative fry-drying process for sewage sludge: a life cycle assessment study

Most adverse environmental impacts result from design decisions made long before manufacturing or usage. In order to prevent this situation, several authors have proposed a new life cycle assessment application: Life Cycle Design (LCD). In this study, LCA is used to assess some selected aspects of the environmental performance of the fry-drying process, which is an innovative drying process for sewage sludge. An analytical comparison between a conventional drying process and the new proposed fry-drying process is reported with reference to some crucial environmental impact categories. The results of this study, applied at the earliest stages of the design of the process, contribute to the evaluation of the fry-drying process for sewage sludge

Origine et post-traitements des digestats : impact sur la dynamique de l’azote et sur la valeur fertilisante azotée et amendante des produits finaux - Résultats du projet DIVA

National audienceDigestates are a key issue for the anaerobic digestion plants management. Indeed these residues from the digestion represent volumes comparable to the volumes of treated inputs and have to be properly valorized in order to ensure good environmental and economic performance of the whole biological treatment scheme. Digestates are generally used as soil improvers or organic fertilisers on cropped soils. Nevertheless the quality of the applied product is largely influenced by the type of organic resources treated in the digester and by the post-processing (phase separation, composting or drying of the solid phase, membrane filtration of the liquid phase, ammonia concentration, etc.). Moreover the way of post-processing and the quality of the final digestate product will influence the environmental impacts after their application. The proposed work aimed at characterizing the quality of different types of digestates and at obtaining mass balances of organic matter and nutrients along post-processing and after spreading. The presented results focus on the fate of nitrogen which is one of the most important nutrients found in digestate

Life Cycle Assessment (LCA) Applied to the Design of an Innovative Drying Process for Sewage Sludge

Most adverse environmental impacts result from design decisions made long before manufacturing or usage. In order to prevent this situation, several authors have proposed the application of life cycle assessment (LCA) at the very first phases of the design of a process, a product or a service. The study in this paper presents an innovative thermal drying process for sewage sludge called fry-drying, in which dewatered sludge is directly contacted in the dryer with hot recycled cooking oils (RCO) as the heat medium. Considering the practical difficulties for the disposal of these two wastes, fry-drying presents a potentially convenient method for their combined elimination by incineration of the final fry-dried sludge. An analytical comparison between a conventional drying process and the new proposed fry-drying process is reported, with reference to some environmental impact categories. The results of this study, applied at the earliest stages of the design of the process, assist evaluation of the feasibility of such system compared to a current disposal process for the drying and incineration of sewage sludge