Selection and application of bacteria for bioclogging of sandy soil
Tan, Wei Wei.
Date of Issue2009
School of Civil and Environmental Engineering
Conventional technologies, such as permeate and chemical grouting, are still lacking in providing an environmental safe and cost effective option for large-scale construction of reservoirs. Hence there calls for more novel technologies which involve indigenous soil microorganisms to modify the soil for an environmental safer option. Bioclogging using slime producing bacteria had been studied to reduce permeability of sand by 4 x 10-3 times over 30 days. Slime producing and oligotrophic bacterium, Caulobacter crescentus, also showed the strongest adhesive strength measured for microbial attachment, which could be tapped on to bind the loose sand particles together. Microbial biocementation using calcium/urea solution and Bacillus pasteurii cells in loose sand core could produce cement that had strength of 0.05 – 5 MPa. This project proposes to study the feasibility of using enriched cultures of oligotrophic and urease-producing bacteria for bioclogging and biocementation methods respectively to reduce the permeability and improve the compressive strength of sand so that it could be used for construction of reservoir. For bioclogging, wet sand sample treated with oligotrophic bacteria for over 30 days reduced the permeability of sand from 1.10 x 10-4 m/s to 5.54 x 10-5 m/s and exhibited an unconsolidated undrained (UU) compressive strength of 71.0 kPa. For biocementation, 30 ml of 1M urea solution, which was mixed with an enriched culture of UPB, and 10 ml of 1M ferric formate produced biocemented sand sample with compressive strength of 149 kPa and permeability of 5.88 x 10-5 m/s after 5 treatments and oven drying. Prior to this, an experiment was conducted to find out the optimum concentration of urea to induce the high pH increase as required by the ferric hydroxide precipitation during biocementation. 0.9 M urea hydroloysis due to the enriched culture of urease-producing bacteria (UPB) was found to increase the pH value from 8.50 to 9.40 within 1.5 to 3.0 hours. To sum up, bioclogging reduced the permeability of bioclogged sand sample (5.54 x 10-5 m/s) more than that of biocemented sand sample (5.88 x 10-5 m/s). However, the duration of bioclogging treatment was about 23 days longer. As for the compressive strength, biocemented sand sample after 5 treatments (149 kPa) was twice as high as that of bioclogged sand sample over 30 days (71 kPa).
Final Year Project (FYP)
Nanyang Technological University