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One of the main concerns about biomass fluidized bed gasification and combustion is the risk of bed particle agglomeration due to ash melting. Although many studies have been conducted about the agglomeration mechanism using silica sand, olivine is mostly mentioned as an alternative bed material for tar decomposition, and its interaction with biomass ash has not been yet fully understood. The aim of this work is to investigate the agglomeration of miscanthus ashes, focusing on thermophysical and thermochemical aspects. Three different bed materials (silica sand (SiO 2 ), raw and calcined olivine ((Mg,Fe) 2 SiO 4 )) and an additive to prevent agglomeration (dolomite (CaMg(CO 3 ) 2 ) were tested. The effects of atmosphere and miscanthus harvest time were also investigated. It was found that the key parameter of agglomeration is the wettability of bed particles by molten ashes. In contact with ashes all three bed material showed good wetting tendencies, while dolomite had non-wetting properties. The adhesion between bed materials and molten ashes increases in the order of silica, olivine and calcined olivine. While in the case of silica sand only physical adhesion occurred, the diffusion of iron oxide into the molten ash was observed using olivine. Calcined olivine has a roughened surface which further increased the adhesion. The atmosphere did not influence the mechanism of ash/bed material interaction. On the other hand, miscanthus harvest time had a significant effect on ash reactivity and interaction with raw and calcined olivine.

Understanding biofilm interactions with surrounding substratum and pollutants/particles can benefit from the application of existing microscopy tools. Using the example of biofilm interactions with zero-valent iron nanoparticles (nZVI), this study aims to apply various approaches in biofilm preparation and labeling for fluorescent or electron microscopy and energy dispersive X-ray spectrometry (EDS) microanalysis for accurate observations. According to the targeted microscopy method, biofilms were sampled as flocs or attached biofilm, submitted to labeling using 4',6-diamidino-2-phenylindol, lectins PNA and ConA coupled to fluorescent dye or gold nanoparticles, and prepared for observation (fixation, cross-section, freezing, ultramicrotomy). Fluorescent microscopy revealed that nZVI were embedded in the biofilm structure as aggregates but the resolution was insufficient to observe individual nZVI. Cryo-scanning electron microscopy (SEM) observations showed nZVI aggregates close to bacteria, but it was not possible to confirm direct interactions between nZVI and cell membranes. Scanning transmission electron microscopy in the SEM (STEM-in-SEM) showed that nZVI aggregates could enter the biofilm to a depth of 7-11 µm. Bacteria were surrounded by a ring of extracellular polymeric substances (EPS) preventing direct nZVI/membrane interactions. STEM/EDS mapping revealed a co-localization of nZVI aggregates with lectins suggesting a potential role of EPS in nZVI embedding. Thus, the combination of divergent microscopy approaches is a good approach to better understand and characterize biofilm/metal interactions.

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