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Author: search.filters.author.Leung, Anthony KwanSubject: search.filters.subject.Hydraulic conductivity

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    Spatiotemporal variations of sand hydraulic conductivity by microbial application methods
    (2024-01-01)
    Kamchoom, Viroon
    ;
    Khattiwong, Thiti
    ;
    Treebupachatsakul, Treesukon
    ;
    Keawsawasvong, Suraparb
    ;
    Leung, Anthony Kwan
    The spatiotemporal distributions of microbes in soil by different methods could affect the efficacy of the microbes to reduce the soil hydraulic conductivity. In this study, the specimens of bio-mediated sands were prepared using three different methods, i.e. injecting, mixing, and pouring a given microbial solution onto compacted sand specimens. The hydraulic conductivity was measured by constant-head tests, while any soil microstructural changes due to addition of the microbes were observed by scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) tests. The amount of dextran concentration produced by microbes in each type of specimen was quantified by a refractometer. Results show that dextran production increased exponentially after 5–7 d of microbial settling with the supply of culture medium. The injection and mixing methods resulted in a similar amount and uniform distribution of dextran in the specimens. The pouring method, however, produced a nonuniform distribution, with a higher concentration near the specimen surface. As the supply of culture medium discontinued, the dextran content near the surface produced by the pouring method decreased dramatically due to high competition for nutrients with foreign colonies. Average dextran concentration was negatively and correlated with hydraulic conductivity of bio-mediated soils exponentially, due to the clogging of large soil pores by dextran. The hydraulic conductivity of the injection and mixing cases did not change significantly when the supply of culture medium was absent.
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    Changes in Pore-Size Distribution and Hydraulic Conductivity of Compacted Soils by Grass-Derived Hydrochar
    (2023-09-01)
    Dong, Huan
    ;
    Leung, Anthony Kwan
    ;
    Chen, Rui
    ;
    Lourenco, Sergio
    ;
    Kamchoom, Viroon
    Hydrochar is a biomass-derived carbon-rich material produced by the hydrothermal carbonization process which requires less energy than the pyrolysis production of biochar. The effectiveness of using hydrochar to amend soil properties, especially hydraulic conductivity, and the underlying mechanism that hydrochar follow remain unknown. This study measured the effects of grass feedstock and grass-derived hydrochar produced at two temperatures (180°C and 240°C) on the pore size distributions (PSDs) and saturated hydraulic conductivity (ks) of compacted silty-clay sand. Hydrochar affected the ks through predominantly the change of macropores of amended soil. Specifically, the addition of 180°C hydrochar [with a 60% specific gravity (GHs) of the soil] at the mass proportion (fH) of 2.5% evolved the PSD from unimodal to trimodal, creating a more open soil structure and increasing the ks by more than half an order of magnitude. When fH exceeded the threshold of 2.5%, the improvement of ks decreased in effectiveness following the compression of macropores. The 240°C hydrochar that has a larger GHs (than the 180°C case) has a high threshold of 5% and introduced a great increase in ks. Test results highlight the importance of avoiding adding excessive hydrochar to prevent the reduction of the effectiveness of drainage improvement.