Integrating Biotechnology into Geotechnical Engineering: A Laboratory Exercise

Abstract

Microbially induced carbonate precipitation (MICP) is a new and promising technique that uses biocementation technology via microbial activities to improve soil properties. This natural occurring biochemical process that utilises the metabolic pathways of bacteria to form calcium carbonate has drawn the attention of scientists, engineers and entrepreneurs to explore various applicable prospects for industrial purposes. The aim of this study was to execute practical activities designed to enable students discover the availability of urease-producing bacteria from local environment and perform a small-scale biocement treatment. Enrichment culture technique and Christensen’s medium were used to screen for urease-producing bacteria from soil samples. Conductivity method was then used to quantify the specific urease activities of the local isolates. A biocement treatment test via MICP process was used to investigate the suitability of using three methods to improve geotechnical properties of loose soils and determine their respective surface strengths. A total of 12 bacterial isolates were obtained from samples collected at Swinburne University of Technology Sarawak Campus. Among these, only eight bacterial isolates (designated as SUTS-1, SUTS-2, SUTS-3, SUTS-4, SUTS-5, SUTS-6, SUTS-7 and SUTS-8) were urease positive. The conductivity results showed that bacterial isolate SUTS-6 had the highest specific urease activity (23.340 mM urea hydrolysed.min-1. OD-1) amongst all the bacterial isolates. This value is comparable to that of Sporosarcina pasteurii DS33 (23.755 mM urea hydrolysed.min-1. OD-1), a control strain used in this study. In addition, the biocement result showed that Group 1 (sand without premix) and Group 2 (sand premixed with bacterial culture) treatment produced more compactible biocemented soil samples when compared with those treated with Group 3 (sand premixed with 1 M urea and calcium chloride). However, the surface strength test revealed that Group 2 treatment method showed the highest strength (430.922 kPa), hence making it the most preferred treatment method.