V3I3P57

Eco-Engineered Rehabilitation of Colluvial Soils in Post-Event Geosites Using a Ureolytic Gram-Positive Bacillus Isolate (C1SBI1) for Biocementation

Yutien Pietro T. Valles¹*, Kathryn Ronika S. Gatilao¹, Love-Vine Cartoneras-Lavador², Jeric C. Biol², Loumelyn Rose B. Bayato¹, Erick Venn R. Rollon¹, Henry F. Haranay¹

Abstract

Climate change effects that have seen to increase the number of landslides and floods have led to rapid erosion of colluvial soils in the regions affected by the disasters. Thus, it is necessary to restore such soils with the help of sustainable stabilization methods. The soil stabilization through MICP mediated by an indigenous bacillus isolate, C1SBI1 was examined in terms of its efficacy in soil strengthening and restoration. The soil samples were treated to isolate bacteria by suspending 5 g of dry soil in 45 mL of sterile diluents (ddH 2 O, 0.85% NA saline, saline + 0.1% peptone), then serially diluted and spread-plated (100 ml of final dilution on NA plates), which were incubated at 30 37 C in 2496 hours. Ureolytic treatment (14 days of the soil with 2% w/v urea + 1% w/v CaCl 2) of the soil led to an increased pH of bio-cemented samples (6.79-7.61 p-value = 0.01) which is an indication of calcium carbonate precipitation. Control and treated soil compression tests showed that treated soil compressive strength increased significantly, with the treated samples retaining the volume of up to 31.00 mm of original 35.00 mm sample height, compared to 21.80 mm remaining in native untreated soil (p-value = 0.00; percent control variation = 5.30). It was also found qualitatively that textural characterization indicated that treated soils turned very soft into firm after squeeze with hands and it revealed the evidence of precipitation, which is more resistant than that of the loose and granular nature of untreated soils. Native soil microbes mediated MICP biomineralization can be extremely useful in improving the texture, shear strength, and consistency of unstable soils, and can be used as a possible alternative to conventional chemical soil stabilization methods since it is relatively less invasive and more environmentally friendly to stabilize the landscape in climate change-prone environments. The paper presents new evidence to support the application of indigenous isolate, C1SBI1, in MICP-based stabilization of colluvial soils as part of a growing yet less established literature on native microbial applications in sustainable soil engineering.

Keywords:

Microbially Introduced Calcium Carbonate Precipitation (MICP), Colluvial Soil Stabilization, Indigenous Bacterial Isolate