Evaluation of stabilized soil by Bacillus sp. HAI4 in different conditions through Taguchi method

Abstract

Introduction: The process of calcite precipitation resulted from metabolic activities by microorganisms is biocalcification. In this process, calcite (CaCO3) is deposited on the soil grains by metabolic activities of microorganisms resulting in increased stiffness/strength and reduced erodibility of soil. Materials and methods: In this study, urea hydrolysis and calcite precipitation rates in soil stabilization process were evaluated by the bacterium Bacillus sp. HAI4 through Taguchi method. Also, it was designed a wind tunnel for analysis of soil stabilization rate. Results: In this investigation, three factors (NH4Cl, urea and molasses) were surveyed in optimization of soil stabilization. Results of this study illustrated that Taguchi method is one of effective methods for optimization of effective factors in soil stabilization process. In this case, urea concentration had higher effect on soil stabilization and calcite sedimentation by Bacillus sp. Also, evaluating factors interaction showed relationship of factors together. Three levels (0.5, 1 and 1.5 g/L), were determined for NH4Cl factor in which the highest effect (4.353%) in soil stabilization was related to level 3. Increasing of NH4Cl resulted in high soil stabilization rate. Three levels 20, 30, and 40 g/L of urea were applied. Results illustrated that effective level was 3 with 4.313%. Also, Taguchi design was in this study, as three levels of molasses (30, 40 and 50 gr/L) illustrated maximum soil stabilization in level 2 by 3.873%. In fact, by increasing of molasses, soil stabilization firstly increased and then decreased. Discussion and conclusion: Totally, this study shows two factors (NH4Cl and urea) that have a major effect in urea hydrolysis and calcite precipitation rates.

Keywords

• Biocalcification
• Soil stabilization
• Bacillus sp
• Urea hydrolysis
• Calcite precipitation
• Ammonium chloride