Experimental Research Of Microbial-Induced Clogging In Sands

Many problems of latent danger and environmental impact of infrastructure projects are due to leakage. The latest research of microbial-induced clogging shows that, suitable survival conditions for microorganisms lead to an effective microbial clogging in a relative short time, to reach the aim of decreasing hydraulic conductivity in soils. In aspects of effectiveness, cost, environment, this technology has many advantages. It is a combination of leakage location and leakage sealing, and has a promising future in leakage sealing of ground and foundation, tunnels, dams and fracture repair in rocks. It is the focus in academy and projects of civil engineering.In this study, tests of microbially-induced clogging were performed to 2 sand columns. Potato soup and glucose were added to the sand columns respectively, and another column was added water only for a control. The hydraulic conductivity of the sand column supplied with enough potato soup decreased to 1/50 of its initial discharge in 3 weeks, and clogging occurred near the leak. The hydraulic conductivity of the sand column supplied with glucose did not change a lot. Then, potato soup was added to the sand column initially served with glucose, and clogging happened near its leak. It showed that microbially-induced clogging with potato soup is repeatable. Clogging stability was tested, and gradient i was improved from 0.267 to 1.067. Clogging was failed. Tests showed that microbially-induced clogging was a combination of leakage location and leakage sealing.In consideration of microbially-induced clogging due to a series of biological, chemical, physical activities, sands from different locations of sand columns supplied with potato soup and water were analyzed in aspects of physics, chemistry and biology. They contain ESEM (environmental scanning of electron microscope) to investigate micro appearance of sand particles, liquid analysis to research the effect of liquid used in the tests during the clogging, the Fe content, XRD (X-ray diffraction) to analyze the change of the mineral composition of sands during the clogging tests, test of loss of ignition to find the change of organic contents, CFU (colony forming units) test to analyze the biomass change during the clogging. The tests showed that the mineral composition of sands during the clogging did not change much, and the organic content near the leak of sand column supplied with potato soup was boosted. This research showed biomass accumulation, EPS (exopolymers) production and production of starch decomposition were main contributions to the clogging.In addition, for a further research of mechanisms of microbial-induced clogging, test conditions of injector test in small scale were studied. It showed that low-oxygen condition was not simulated well, from PVC-sand column in large scale to injector test in small scale. Test conditions need to be improved, to simulate the low-oxygen condition, to lead to effective microbilly-induced clogging in small scale, and it is crucial to study mechanisms of microbilly-induced clogging.This study has important reference value to the research and application of microbially-induced clogging in sands.