Optimization of microbial fermentation processes using RSM approach for soil improvement
摘要
The current work relates to the optimization of the microbial fermentation process through Response Surface Methodology (RSM) approach for improving the soil compressive strength by Microbially Induced Calcite Precipitation (MICP). The ureolytic bacteria selected for the study were Geobacillus stearothermophilus and Acetobacter xylinum, based on maximum specific urease activity. The organisms were further tuned for a variety of growth factors, such as calcium carbonate molarity, urea concentration, inoculum size, and reaction time, for effective deposit calcium and improvement of soil strength in engineering aspects. Attempt for flask-based optimization approach was made for the primary analysis and for further use of the Central Composite Design of RSM for detailed examination of growth parameters like calcium chloride concentration, urea concentration, inoculum size and reaction time. Based on RSM, optimized condition for Geobacillus stearothermophilus, 3mM of calcium chloride, 8% of urea, 3 McFarland Standard and 48 h of reaction time and for Acetobacter xylinum, which are 4mM of calcium chloride, 8% of urea, 2 McFarland Standard and 96 h of reaction time were determined. The Geobacillus stearothermophilus and Acetobacter xylinum treated soils were then subjected to unconfined compressive strength analysis for the determination of the soil strength. At highest soil density, Geobacillus stearothermophilus treated red soil attained axial stress of 380 kPa at a strain level of 5.55 whereas, the strength of Acetobacter xylinum treated soil was found to be comparatively low and the calcium yield was also very minimal when compared with the calcium yield of Geobacillus stearothermophilus. This extensive research study has provided conclusive evidence of the ability of Geobacillus stearothermophilus mediated MICP to seal voids and create a revolution in modern day engineering and construction.