Microbially induced carbonate precipitation (MICP) is a process that has emerged as an attractive alternative ground improvement technique in Geotechnical and Civil Engineering using ureolytic bacteria for soil strengthening and stabilisation. Locally isolated Sporosarcina pasteurii from limestone cave samples of Sarawak were found to have high urease-producing abilities. Optimisation of various cultural conditions (incubation temperature, initial pH medium, incubation period and urea concentration) were performed using conductivity and optical density measurements to determine the maximum specific urease activity. In addition, an in vitro biocement test was done to define the prospect of using these bacterial isolates in civil engineering work for the improvement of soils with inferior properties. The experimental results showed that urease activities were optimum at 25 to 30°C, pH 6.5 to 8.0, 24 hr incubation and 6 to 8% (w/v) urea concentration. It was also demonstrated that biocementation using the local ureolytic bacteria can improve the strength of poorly graded soils. However, the efficiency of the MICP process in improving the soil's strength varied among samples treated with different bacterial cultures.

Urease is a key enzyme in the chemical reaction of microorganism and has been found to be associated withcalcification, which is essential in microbially induced calcite precipitation (MICP) process. Three bacterialisolates (designated as LPB19, TSB31 and TSB12) were among twenty-eight bacteria that were isolated fromsamples collected from Sarawak limestone caves using the enrichment culture technique. Isolates LPB19, TSB31and TSB12 were selected based on their quick urease production when compared to other isolates. Phenotypiccharacteristics indicate all three bacterial strains are gram-positive, rod-shaped, motile, catalase and oxidasepositive. Urease activity of the bacterial isolates were measured through changes in conductivity in the absence ofcalcium ions. The bacterial isolates (LPB19, TSB12 and TSB31) showed urease activity of 16.14, 12.45 and 11.41mM urea hydrolysed/min respectively. The current work suggested that these isolates serves as constitutiveproducers of urease, potentially useful in inducing calcite precipitates.

The process of ureolysis-driven biocementation is used to improve granular soils. The precipitation of calcium carbonate (CaCO3) crystals results from the reactions of urease generated by ureolytic bacteria and chemical reagents, which strengthen or bind soil particles together. Using a lab-based scaled physical model, this paper investigated the influence of selected spacing intervals (107 mm, 214 mm and 321 mm) on the effectiveness of biocementation via the injection-suction or ‘push-pull’ approach. Polystyrene moulds were used to create soil specimens. It was then injected with 6 cycles of the treatment solutions at the intervals stated. The compressive strengths and CaCO3 content of the biocemented soil specimens were measured after curing, as well as scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared (FTIR) spectroscopy, and effluent analysis (pH and ammonium measurements). The biocemented soil specimens with different spacing intervals obtained compressive strengths of 2.53 ±1.06 to 4.2 ±2.3 MPa, while the CaCO3 contents were from 2.78 ±0.3 to 11.16 ±1.5%, respectively. The elemental compositions and bonding of CaCO3 precipitates in the biocemented soil were confirmed by EDS and FTIR spectra, while SEM micrographs revealed chip-like and irregular rhombohedral crystal forms. The results demonstrated that injection spacing had an effect on MICP-treated biocemented soil.