Document Type : Research Article
Authors
Urmia University
Abstract
Introduction: Dust is one of the most important destructive phenomena in the world, that annually causing damage to human health and the environment. This issue ranks after two major challenges of climate change and water scarcity as the third most important challenge facing the world in the 21st century that is considered. Microbial-induced calcite precipitation (MICP) is a relatively green and sustainable soil improvement technique. It utilizes biochemical process that exists naturally in soil to improve engineering properties of soils. The calcite precipitation process is uplifted by the mean of injecting higher concentration of urease positive bacteria and reagents into the soil. In this process, the enzyme present in the bacteria hydrolyzes the urea in the environment and through reacting with the calcium ion, leads in the deposition of calcium carbonate. The main objective of this study is isolation native ureolytic bacteria from different soil of around Urmia Lake and then, the evaluation their efficiency in the MICP for stabilization of sandy soils and reduce windy erosion.
Materials and Methods: In order to isolate ureolytic bacteria, 25 soil samples were taken from different land use in West Azarbaijan province, Iran. To increase the number of ureolytic bacteria in soil samples were used from the enrichment solution and then ureolytic bacteria were isolated and purified. These isolates were subjected to various biochemical tests, as well as the growth curve and urease activity were determined. In order to investigate the potential for soil improvement, a factorial experiment was conducted based on a completely randomized design with two factors including microbial treatment in eight levels (including five isolated bacteria (U3, U8, U16, U35 and U40) and Bacillus pasteurii (as control Positive), non-bacterial and non-cementation (as control negative) and non-microbial but with cementation solution treatments) and another factor including different concentrations of calcium chloride solution with urea at three levels (0.1, 0.5 and 1 molar), in three replications. After injection of cementation solution and bacterial solution to soil, penetration resistance and windy erosion rates in sandy soil were assessed
Results and Discussion: In study, overall 45 isolates of the bacteria were isolated and purified. Among of 44 isolates, five bacterial isolates (U3, U8, U16, U35 and U40) had the highest urease activity. The growth curve of bacterial isolates showed that the highest urease activity and microbial population were in the time period of 13 to 16 hours after microbial culture, which it is represents the best time use bacterial solution in the MICP process. According to the results of soil improvement tests, the amount of soil erosion in the MICP treatment at a wind speed of 25 m/s was zero and the rate of penetration resistance was averaged over 13 MPa, which has a very impressive impact on MICP in controlling wind erosion, especially at high speeds of wind. The results showed that U3 and U16 isolates had the highest amount of urea hydrolysis and also U16 and U3 had the lowest and the highest tolerance to salinity, respectively. The results of the wind tunnel showed that the wind erosion threshold in negative control samples (non-bacterial and non-cementation) were 9.4 m/s and for MICP samples (including five isolated bacteria and Bacillus pasteurii ) were much higher than the wind tunnel speed in the wind tunnel machine in Urmia university (25 m/s). The maximum penetration resistance (13.5 MPa) was obtained in the sample treated with U3 isolate and 1 molar calcium chloride, but negative control treatments (non-bacterial and non-cementation) as well non-microbial but with cementation solution treatments were 0 and 97.0 MPa, respectively.
Conclusion: The amount of soil wind erosion was zero in MICP treatment with the wind tunnel speed 25 m/s that indicates very important effects MICP to control wind erosion of sandy soils to compare control treatments (non-bacterial and non-cementation and non-microbial but with cementation solution) in high wind speeds. The application of MICP treatment in the soil, in addition to increasing its wind erosion resistance, also increased penetration resistance in the soil. Increasing the penetration resistance of MICP treatments (including five isolated and Bacillus pasteurii) can be due to the activity of bacterial isolates, chemical interactions, and the formation of calcium carbonate precipitation into soil cavities, which causes to form a hard layer in soil. Also, obtained resistance by using isolated bacteria indicates that there are many unknown microorganisms that can carry out MICP better than Bacillus pasteurii and probably they will be better compatible and establish because they are native.
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