Microbial calcium carbonate, by bridging sand particles, can play an important role in sand dune stability. A study was carried out on the cementation of sand grains and infilling of pore spaces by CaCO3. Two bacterial species (SPOROSARCINA PASTEURII and SPOROSARCINA ureae), three reactant concentrations (0.5, 1 and 1.5M), and six reaction times (12, 24, 48, 96, 192 and 288 hours) were tested in factorial experiment. Bacterial inocula and reactant solutions were added daily to sandy soil columns (6.5 cm height and inner diameter of 7.7 cm), while precipitation of CaCO3 being investigated within 0-1.5, 1.5-3, 3-4.5 and 4.5-6 cm intervals. Chemical and micromorphological analyses revealed that CaCO3 formation, inorganic C sequestration, and depth of cementation were more profound for S. PASTEURII as compared with S. ureae. Both microbial CaCO3 precipitation and inorganic C sequestration increased with increase in reaction time from 12 to 288 hours. Increase in reactant concentration also caused an increase in CaCO3 precipitation (by 12%). Micromorphological observations showed a high degree of calcite crystals’ bridging, coating on sand particles and as well infilling of pore spaces. S. PASTEURII is thus recommended for being used in stabilization of sand dunes; due to its significant effects on CaCO3 deposition and as well on sand grain cementation.

Biological cementation is a new process in which urea hydrolysis bacteria or free urease enzyme decompose urea and increases the pH of the environment and chemical interactions in the presence of calcium ions to form calcite. Nowadays, nano-calcite is widely used in engineering, such as increasing the strength of soil and concrete, as well as in medicine, such as drug delivery and cancer treatment. This study aimed to investigate the laboratory conditions for producing nano-calcite particles with appropriate quality, size and purity by SPOROSARCINA PASTEURII enzyme extract for use in medical and engineering studies. This investigation aimed to make calcite by S. PASTEURII enzyme extract and optimize influential factors in calcite production. For this purpose, the bacterium S. PASTEURII was cultured in nutrient broth containing urea and nickel, and upon reaching the appropriate time, the cells were separated and washed. Then, their enzyme extract was prepared by sonication, and calcite precipitation was studied in different amounts of urea, calcium chloride, enzyme and temperature. The quality of produced calcite crystals and their ratio compared to other crystals were investigated by XRD and SEM analyses. According to the results of XRD analysis, it was found that in 0.5 M urea and 0.25 M calcium chloride, the highest amount of calcite is produced with 96%, and the least side products are produced. Examining the particle size histogram in the sample containing 0.5 M urea and 0.25 M calcium chloride revealed that the range of particles were between 50 and 100 nm. The nature and type of crystals were studied by electron microscopy, and EDX analysis showed the presence of calcium, oxygen, and carbon. According to the results, it was found that by the increase of the concentrations of urea and calcium, the range of particle size became larger. Also, the percentage of calcite produced in low urea and calcium chloride concentrations is higher than those in high concentrations.

Fast growing of engineering infrastructure to meet human requirements is directly related to the need for a resistant soil to carry out construction load. On the other hand, the importance of environmental issues has led to an ever-increasing demand for new and environmentally friendly methods for soil remediation. The method of microbial induced calcium carbonate precipitation (MICP) is considered by the researchers as one of the most environmentally friendly methods. The purpose of this study was to investigate the effect of MICP on the uniaxial strength of carbonate sand. Therefore, samples of Bushehr carbonate sand were cured after the injection of bacteria and cement solution. Then a uniaxial compression tests were carried out to evaluate the compressive strength. Also, the effect of cement solution concentration and curing time on the results of MICP method was investigated. The results show that maximum uniaxial strength of sand stabilized with MICP is about 3. 5 kg/cm2, which indicates the proper performance of MICP method for stabilization of carbonate sand. The UCS of the samples depends on the concentration of cement solution. Stabilized samples with a higher cementation of concentration solution had more uniaxial resistance than samples with lower cement concentrations. The curing time more than 14 days did not significantly affect the uniaxial resistance.

Wind erosion and its dust are serious danger in erodible soil degradation, environment, air pollution and human health. It is an important problem in Iran and especially in Khuzestan province. In the current research, the effect of SPOROSARCINA PASTEURII bacteria in Tryptic Soy Broth (TSB) and sugarcane molasse as a culture media on wind erosion was investigated. The sandy soil sample was obtained from the Hamidyeh area in the Azadegan plain of Khuzestan province and the effect of time and culture media on the test was considered. The treatments were conducted with sugarcane molasse (10%) and TSB as a culture media and urea (2%) and calcium chloride as an injection solution. The experiment was carried out with the basis of completely randomized design with three replications. After 7, 15 and 30 days of injection, calcium carbonate content, penetration resistant and erodibility by wind tunnel were considered. Results showed that the highest concentrations of calcium carbonate were observed under 10% molasses treated with bacteria, which increased the percentage of calcium carbonate by 52%. The highest resistance to penetration was related to treatment 10% molasses application, which resulted in an increase of 1000 times the penetration resistance. The penetration resistance and the percentage of calcium carbonate accumulated in the soil showed a significant increase at the 5% level by LSD test, over time. The investigation of erodibility for selected samples was performed in wind tunnel with an average wind speed of 16 m/s. The amount of erosion in the sandy soil was decreased from 52% to zero, which indicates a 100% reduction in erosion. The results of this study indicate the significant role of molasses in reducing the erodibility of sandy soil and increasing the penetration strength. Thus, it can be suggested as a method to stabilize the sand.

Wind erosion and the phenomenon of Dust with all of its controlling methods is serious problem. This phenomenon lead environment degradation and fugitive dust storms. So, Study and use of the new methods to control this natural phenomenon is essential. In this study, the novel and environmental friendly method of soil biological stabilization was investigated with using an abundant bacterial species founding in nature and soil deposits. The scientific name of this bacterium is SPOROSARCINA Pasturii (PTCC 1645) and uses as the urease-positive bacterium. This bacterium produce urease enzyme which converts urea to ammonium and carbonate, resulting in the precipitation of calcite crystals that bridge the soil particles. In this study a mixture of cementation and bacterial-cell solutions uniformly sprayed onto the exposed top surfaces of the soils. The concentration of bacterial-cell solution was quantified in terms of its optical density at 600nm wavelength (OD600) which equal 1.5 (that is, approximately 1.5×108 bacterial cells·ml−1). The prepared equimolar urea–calcium chloride cementation solution included nutrient broth (3g.l-1), ammonium chloride (10g.l-1) and sodium bicarbonate (2.12g·l-1) prepared at 0.5M concentration. The mixture volume sprayed onto each specimen was equal to 1.5Vv (where Vv is the pore voids volume of the topmost 3-mm thick layer of the 20–mm deep loose sand tray-specimens). The bench scale experimental programme presented investigates the proposed technique’s effectiveness for stabilisation of two clean, angular to sub-angular medium silica sands and carbonate silty sands with different gradations (sand t60 and sand t90 with size ranges of 0.125–0·50 and 0.075–0.85mm, respectively and carbonate sand with size ranges of 0·001–0·85mm, and mean particle size (D50) values of 0.28, 0.24 and 0.20 mm, respectively), the time-dependent (retention time 3, 7, 14, 20 and 28 days) compressive strength development for the crustal sand layer following single- and double-MICP (with interval of 6 days) spray treatments, as well as wind tunnel experiments under the condition of wind velocity of 20 ms-1. The effect of dew formation on crustal compressive strength development with curing period and the efficiency of the MICP treatment for the outdoor environment compared to laboratory-controlled test conditions. A pocket penetrometer was used to determine the compressive strength of soils. Significant improvements in the Compressive strength of the treated soil samples were observed. The results show improving compressive strength with time. The highest compressive strength in the carbonate sand was obtained equals to 84 kPa. Silica sand with finer size distribution has shown more compressive strength than two other soils. Also the results showed that double-MICP spray treatments of the bacteria solution and cementation was more effective than single- MICP spray treatments in the compressive strength of soils, especially in the silica sand equals to 190% in a curing period of 28 days. Also, the cured MICP-treated crustal sand layer was stable to 20 m·s−1 winds that demonstrating the potential of biological stabilisation via the MICP process as an appropriate option for dealing with desertification and motion of sandy soil deposits.

Bio-cementation is a new process in which urea hydrolyzing bacteria decompose urea into ammonia and produce calcium carbonate crystals in higher pH due to the production of an alkaline environment. The aim of this study was to investigate the production of calcite using S. PASTEURII in precipitation medium and optimization the factors affecting on this reaction. In addition, in this study, the effect of carbon sources in precipitation medium was studied. In this study, according to the results of quantitative XRD analysis, it was found that 1% urea with 94% calcite, 2.4% vaterite and 2% calcium with 92.3% calcite, 4.9% vaterite productivity, respectively, were the best condition for the highest calcite productivity in precipitation medium. Particle size analysis using FESEM revealed that particles produced in 1% urea were often in the range below 100 nm. With increasing urea concentration, the frequency of particles below 100nm in size decreased. The particle size distribution showed that the particles of less than 100nm were lower in 2% urea compared to 1%.FESEM analysis showed that with increasing calcium chloride particles of less than 50nm decreases significantly. The same was true of urea, and it was found that the particle size of the crystals increased at high concentrations of the reactants. In addition, the effect of the presence of carbon sources in the precipitation medium on the production of calcium carbonate crystals was also investigated, which was not significantly different from their absence ( glucose and sucrose). Maltose sugar decreases calcite and increases other crystals.