Development of a Ureolytic Bacterial Consortium for Beach Sand Stabilization Using Bio-Grout Technology: A Preliminary Laboratory-Scale Study

Abstract

Coastal abrasion poses a serious threat to the coastal regions of Indonesia. Conventional soil stabilization methods using Portland cement have high carbon footprints and can disrupt aquatic ecosystems. Bio-grout technology based on Microbially Induced Calcium Carbonate Precipitation (MICP) offers a green alternative by utilizing the activity of calcium-carbonate-precipitating bacteria. This study aimed to develop a consortium of ureolytic bacteria and determine the optimal application protocol for beach sand stabilization at the laboratory scale. Experiments were conducted using Tambakboyo beach sand (grain size 0.1–0.5 mm) with variations in bacterial density (10⁵, 10⁷, 10⁹ cells/mL) and number of treatment cycles (1, 3, 5 cycles). The measured parameters included Uniaxial Compressive Strength (UCS), CaCO₃ precipitation percentage, permeability, and simulated erosion resistance. The results showed that the optimal condition—bacterial density of 10⁷ cells/mL with 3 treatment cycles—produced a UCS of 2.1 MPa, CaCO₃ precipitation of 5.1% by weight, and mass loss of <3% after simulated water flow at 0.5 m/s. The control treatment without bacteria (chemical injection) yielded only ~0.1 MPa UCS and <0.5% CaCO₃ precipitation, confirming the crucial role of bacteria as biological catalysts. Excessive bacterial density (10⁹ cells/mL) led to premature pore clogging and a drastic reduction in permeability. This study concludes that a ureolytic bacterial consortium at a density of 10⁷ cells/mL with 3 injection cycles represents the most effective and efficient condition for forming a natural bio-cement capable of mitigating coastal abrasion. Further research is required to assess scalability, the ecotoxicological impacts of ammonium byproducts, and long-term field stability.