A microbial method for improving salt swelling behavior of sulfate saline soil by an experimental study

Services of soil environment system and safety production of pavements and railways are seriously affected and threatened by salt swelling behavior of sulfate saline soil. To improve the salt swelling, a microbial method using sulfate-reducing bacteria (SRB) was presented, based on the metabolism-reduction mechanism of SRB. First, the SRB was domesticated in an increasing sodium sulfate environment up to adapt the salinity of saturated sulfate saline soil. Then the salt swelling contrast tests of sulfate saline soil with and without SRB during the cooling process were conducted. Effects of temperature and salinity on salt swelling displacement, salt swelling reduction value, and salt swelling reduction rate of sulfate saline soil with and without SRB were investigated. The test results of X-Ray Diffraction (XRD) and Deoxyribonucleic Acid-Polymerase Chain Reaction (DNA-PCR) were used to verify and explain the reduction and reduce-swelling mechanism (RRSM) of SRB on sulfate saline soil. Test results as follows: (1) SRB strain-A resistant to a high concentration sulfate was obtained through multiple domestications, and had a significant reduction and reduce-swelling effect (RRSE) on sulfate saline soil. (2) Salt swelling displacement of sulfate saline soil with and without SRB increases with increasing salinity and decreasing temperature, but the maximum salt swelling displacement of sulfate saline soil containing SRB was less than that without SRB. (3) SRB has a significant inhibitory effect on salt swelling of sulfate saline soil. The maximum reduction rate of salt swelling was 32.96% (2% salinity) and the minimum one was 11.54% (5% salinity). (4) Low temperature and high salt concentration environment inhibited SRB activity and hindered the SSRE of SRB. The reduction rate of salt swelling by SRB decreased continuously with the increase of salinity and presented an exponential function change trend. (5) Results of the DNA-PCR and XRD have effectively verified the occurrence of the RRSE of SRB. This research proves that the microbial method using SRB to improve the salt swelling is feasible and is of great significance for sulfate saline soil treatment. Keywords: Sulfate saline soil, Sulfate-reducing bacteria, Salt swelling displacement, Reduction and reduce-swelling effect, Microbial treatment