Bio-Mediated Soil Improvement Using Plant Derived Enzyme in Addition to Magnesium Ion

• Main Authors: Md Al Imran, Kazunori Nakashima, Satoru Kawasaki
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Crystals
• Subjects: enzyme-induced carbonate precipitation (EICP); urease activity; Mg²⁺/Ca²⁺ ratios; watermelon seeds; CaCO₃ morphology; soil improvement
• Online Access: https://www.mdpi.com/2073-4352/11/5/516

Recently, soil improvement using EICP (Enzyme-Induced Carbonate Precipitation) methods in the geotechnical and geo-environmental field has become a prominent interest worldwide. The objective of this study was to develop an improved extraction technique of crude urease from watermelon seeds in both dry and germinated conditions. Subsequently, this study also analyzed the improvement methodology of crystal polymorphs and soil bonding incorporation of various Mg²⁺/Ca²⁺ ratios. The optimization of enzyme-mediated carbonate precipitation was also investigated by Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) analysis. Results confirmed that the precipitated crystals are mainly calcite, vaterite and aragonite primarily (depending on the Mg²⁺/Ca²⁺ ratios). Therefore, to improve the bonding capacity in between the sand particles a novel improvement methodology was investigated by adding various Mg²⁺/Ca²⁺ ratios. The mechanical properties of the treated soil (Mikawa Sand, <i>D</i>₅₀ = 0.870 mm) specimens were tested by unconfined compressive strength (UCS) and this confirmed the effectiveness of adding various Mg²⁺/Ca²⁺ ratios. The results of the UCS tests showed that, the lower molar ratios of Mg²⁺/Ca²⁺ can significantly improve the UCS of the specimen (up to 50%) which could be considered a significant outcome for different bio-geotechnical applications.