a b s t r a c tThe objective of this work is to give the fundamental information that should be known about wastewater sludge drying. Three methods are mainly applied: convective drying, conductive drying and solar drying, each one presenting different characteristics. When applying convective drying three phases are distin guished: adaptation phase, constant drying rate phase and falling drying rate phase. Experimental works show that several parameters influence the drying kinetic during this process, such as the origin of the sludge and operating conditions. Imaging techniques allow observing three phenomena that happen during convective drying: shrinkage, cracks and skin formation. When applying conductive drying and considering the torque variations, the product passes through: pasty phase, lumpy phase and granular phase. The results show no regular shape of the drying kinetic with high values of the drying rate and the heat transfer coefficient during the first phase. A special focus is given into the sticky phase which reduces performances of the dryer. The third applied drying method is solar drying, which depends wholly on climatic conditions, such solar radiations and air temperature. Besides, for this method no regular shape of the drying kinetic can be observed, with high drying rate values during favorable conditions and low drying rate values during unfavorable conditions. The presented studies dealing with solar drying of wastewater sludge are limited to the variations of the different air temperatures registered inside and outside the drying chamber with the product temperature and their humidity with study of the pathogen reduction. Finally, some innovative developed methods are exposed in this review, such as the use of frying and super heated steam.

Resorcinol-formaldehyde gels were produced at 50, 70 and 90°C and with three different R/C ratios (500, 1000 and 2000). The effect of these variables combined with that of aging time was studied in order to optimize the synthesis conditions. The convective air-drying process was used, and the drying duration was studied with regard to the synthesis conditions. The aging time has no effect on the pore texture after 24 h at 90°C or 48 h at 70°C, whatever the R/C value. The synthesis-aging step can be shortened by increasing the temperature.Nevertheless, the pore size tends then to decrease, especially when R/C is high, but this can be counterbalanced by increasing R/C. Moreover, bubbles often appear in the gel at high synthesis temperature, which limits the temperature to about 70°C in the case of monolithic parts. At 70°C and with an air velocity of 2 m/s, the elimination of 90% of the solvent Manuscript 2 requires 1 h drying when the pore size reaches 400-600 nm, 2.5 h for 50 nm wide pores and 3 h when the pore size decreases to 15-20 nm. The drying duration does not exceed 8 h in all cases and could be shortened by increasing the temperature at the end of the process.

The three space fillers allowed bone formation to occur. Nevertheless, augmented volumes declined in the Clot and Auto groups, while they remained stable with BHA. A slowly resorbable biomaterial might be suitable in sub-sinusal bone augmentation for preventing the re-expansion process and for augmenting the density of the regenerated tissues.

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X-ray microtomography is proposed as a new tool to investigate the evolution of size, shape and texture of soft materials during a drying operation. This study is focused on the drying of mechanically dewatered sludges from a secondary wastewater treatment. The shrinkage phenomenon is shown to play a crucial role in the control of the drying process. The shrinkage curves are determined by analysing the shape and size of cross sectional microtomographic images of sludge extrudates at different levels of drying. The observation of drying and shrinkage curves allows us to determine 3 critical water content values, which define different drying zones where extragranular, intragranular or mixed limitations prevail.When drying is externally controlled, the decrease of the drying rate observed during experiments can be related to the reduction of the external area of the sample, i.e., to shrinkage. When drying is internally controlled, resistances inside the solid govern the process. Between these two extreme situations, the drying rate reduction is the result of both the external area decrease and the development of internal resistances limiting drying. A multizone model is proposed to describe quantitatively these observations. The analysis of the internal texture of the sludge extrudates reveals crack formation at the end of the drying process. The onset of crack formation is clearly related to the appearance of internal transfer limitations, i.e., humidity and temperature gradients inside the material.

Packing simulations of generic, nonspherical pellets were performed and compared with experimental data sets obtained using X-ray computerized tomography (CT). Two modified versions of what was previously a purely geometrical, digitally based packing algorithm were implemented. Both are aimed at incorporating the effects of particle interaction forces, one utilizing the distinct element method (DigiDEM) and the other an intermediate solution (collision-guided packing or DigiCGP). This article summarizes the models and the simulations performed using these two modified versions of DigiPac and, for model validation purposes, compares the predicted results with the corresponding X-ray tomographic scans of packed columns, in terms of bulk density, local packing density profiles, and pellet orientation distributions. For packed beds of relatively large and identical pellets, the simulation results indicate that particle-particle and particle-wall interactions cannot be ignored if realistic packing structures are to be obtained by simulation and even a simplistic treatment of these interactions can produce significantly more realistic packing structure than none at all.