Introduction: The present study was focused on the statistical optimization of growth parameters for enhancing the Microbially Induced Calcite Precipitation (MICP) using ureolytic yeast strain.
Materials and Methods: Thirteen yeast strains were tested for the synthesis of urease enzyme by phenol-hypochlorite assay and were further evaluated for calcite precipitation test. The growth parameters were optimized using the best ureolytic strain by Box-Behnken Design (BBD) and the extracted MICP was characterized through instrumental analysis.
Results: Among thirteen yeast strains, Candida tropicalis NN4, Spathospora sp. NN04, Wickerhamomyces anomalus VIT-NN01 and Candida dubliniensis NN03 showed positive results for the synthesis of urease enzyme. Spathospora sp. was found to be the most potent strain for MICP. A significant enhancement in MICP by Spathospora sp. was observed under optimized conditions viz. A-urea concentration (80.0 g/L), B-calcium chloride (45.0 g/L), C-pH (9.0) and D-inoculum dosage (8%, v/v). The actual value (34.4±0.12 g/L) was in agreement with predicted value (34.7±0.01 g/L) with the R² value (0.9900), confirming the validity of the model. The FTIR of MICP confirmed the fundamental bands of CO₃ stretching and bending vibrations, observed at 1394.23 and 874.85 cm^-1. The Scanning Electron Microscope (SEM) images of biomotar revealed aggregated polymorphs of MICP interconnected with yeast mycelium and spores. The Energy Dispersive X-Ray Spectrometer (EDX) analysis indicated the presence of calcite in the biomotar. A remarkable improvement in the compressive strength (28 to 44 MPa) and morphological changes were observed in biocement mortar as compared to cement mortar.
Conclusions: This result is the first report on the implementation of ureolytic Spathospora towards the application of biocementation through MICP using BBD.