Extraction of Soil-Based Fungal Urease and Its Application for Bio-Cementing Sands with Subtle Permeability Reduction

In this study, multiple samples were collected from different urea-fertilized agricultural lands, and their fungal strains were isolated using the tenfold serial dilution method on potato dextrose agar plates. In total, 21 strains were identified as urease-positive through primary screening on Christensen medium. Secondary screening of selected fungal isolates conducted through submerged fermentation could then identify the fungal strain 10−5 S11 brown as the most effective urease producer that exhibited maximum urease activity (682 U/mL/min). It was identified by scotch tape microscopy for morphological characterization and subsequently confirmed through 18S rRNA sequencing as Aspergillus terreus. Further, optimization of fermentation conditions showed that M9 medium containing 1.5% urea as a nitrogen source at pH 5.5, in addition to 3% sucrose as a carbon source, 4% inoculum size, and 7 days of incubation at 30 °C, produced the best fermentation and enhanced the urease activity from 682 U/mL/min to 1050 U/mL/min. Subsequently, the optimized urease enzyme was mixed with clean sand to induce carbonate precipitation to enhance its unconfined compressive strength from 22.5 kPa for untreated samples to 154.2 kPa for treated samples after 28 days, with subtle permeability reduction from 4.26 × 10−3 cm/s to 1.7 × 10−3 cm/s.