Drying of porous media is of significant importance in many fields ranging from hydrology and agriculture, to industrial applications, e.g., food sciences and chemical engineering. The drying process depends on both the external atmospheric conditions and structure of the porous medium. Previous research has shown that hydrogel produced by plant seeds/roots or bacteria can change the physical and hydraulic characteristics of porous media, however, the role of hydrogel on the drying process remains unclear. In this study, we measured water evaporation in Accusand (40/50 mesh) as influenced by bacterial EPS (extracellular polymeric substances; produced by Bacillus subtilis strain FB17) and a bacterial EPS surrogate xanthan using weight measurements and neutron radiography imaging (NRI). Less evaporative water loss, slower Stage I evaporation, and shorter duration of Stage I evaporation were observed for EPS-amended samples than their corresponding controls. We discussed three mechanisms that are potentially responsible for the observed EPS effects, (1) large water holding capacity of EPS, (2) broader effective pore size distribution, and (3) modification in physicochemical properties (reduced surface tension and increased viscosity) due to EPS presence. These findings improve our understanding of the drying process as affected by hydrogel, with the potential application in engineering rhizosphere for agriculture production under restricted water availability.
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