Biological soil improvement using new environmental bacteria isolated from northern Iran

Abstract

New indigenous bacteria, extracted from soil samples that had been collected from different parts of Iran, were introduced to improve dune sand using microbially induced carbonate precipitation (MICP) as an environmental engineering method. In order to isolate urease-producing bacteria from local alkaline soils, a series of standard tests was conducted to evaluate the urease performance and potential of calcium carbonate (calcite) sedimentation. Based on their properties, the bacteria with the best performance were identified by 16S ribosomal ribonucleic acid sequencing. To achieve a better understanding of the performance of the selected isolates, Sporosarcina pasteurii was employed as the control sample. The geotechnical behaviour of bio-mediated sand was studied through a series of geotechnical experiments, including unconfined compressive strength (UCS), constant-head permeability and wind erosion tests. The influence of freeze–thaw cycles and the durability of specimens on the UCS was also investigated. It is worth noting that sand MICP-treated by Bacillus sp. UTMC 2623 gave a performance relatively equal to that of the control sample during all UCS tests. Scanning electron microscopy images and X-ray diffraction were also used to observe calcite precipitation formation using Bacillus sp. UTMC 2623, which indicated precipitation of calcite throughout the sand column.