Study On The Influence Of Gram-negative Bacteria On Saturated Permeability Of Loess

Soil is not only the home of microorganism,but also the natural medium for its growth and reproduction.The physical and chemical properties of the aqueous solution can significantly affect the growth of microbes in the solution.When the nutrients in the water source enter the soil,the soil moisture is changed and the soil moisture becomes instability.Such problems as soil compaction and soil loss occur.The change of soil physical and chemical properties affects microorganisms in the soil,causing the change of microbial species,causing damage to soil and soil microbial environment.At the same time,C,N,P,K and other elements in water nutrients play an important role in the growth of microorganisms in soil,and also change the physical and chemical properties of soil.Therefore,the significance of the influence of water nutrients on the permeability of Malan loess lies in the study of the growth propagation and metabolism of soil microbes under the interference of water source nutrients,especially the influence of carbon-nitrogen ratio on soil permeability in water source nutrients,and promote the virtuous cycle of soil.In this paper,indoor test and theoretical analysis are combined.Take Malan loess of Jingyang,Shaanxi as an example.The gram negative bacteria in Malan loess as the test strain,control the different C/N ratios in the nutrient solution and the initial number of bacteria in the soil,study the influence of the Malan loess saturated permeability coefficient and the change regulation.Through analyzing the species,quantity,growth rate,EPS and surface free energy of soil samples,studied the internal mechanism of loess permeability change rule.The following knowledge and conclusions are drawn from the experimental investigations.(1)There are general bacteria,fungi,Gram-positive bacteria and gram negative bacteria in Ma Lan loess,among which gram negative bacteria are the majority.In addition,in the analysis of the growth characteristics of Gram-negative bacteria,the growth rate of the Gram-negative bacteria in the basal medium was increased by the C/N ratio from 5:1 to 40:1.(2)During the whole penetrant test,with the increase of seepage distance,the chocking-up degree of Gram-negative bacteria in soil samples gradually decreased.From the point of penetration time,at first,the permeability of soil samples did not change significantly.With the increase of infiltration time,the permeability of soil samples decreased rapidly,and the blockage of gram negative bacteria occurred rapidly in soil samples.In the last stage of infiltration,Gram-negative bacteria have completely blocked soil samples,and the permeability of soil samples has gradually stabilized.(3)Under the simulated seepage condition,permeability of soil samples with different C/N rations,with the increase of C/N ratio,the soil permeation rate decreased faster.The permeability of soil samples with different initial gram negative bacteria increased faster with the increase of initial bacteria number.The soil samples without added strains and and the source of water was deionized water,the permeability of soil samples basically remained unchanged in the early stage,but only slightly decreased in the latter stage.(4)After the end of the penetrant test,all permeable soil surfaces under nutrient supply conditions were observed biomembrane,however,soil samples under deionized water supply conditions weren't observed biomembrane.The surface free energy of gram negative bacteria in soil samples under nutrient supply conditions were measured.The surface free energy of gram negative bacteria with different C/N nutrient solution from large to small is: 5:1>20:1>10:1>30:1>40:1.(5)The decrease of soil permeability coefficient is caused by many factors.One is that the growth characteristics of Gram-negative bacteria are different due to the difference of C/N ratio and initial bacteria number.The two is the biofilm formed by the growth and metabolism of Gram-negative bacteria on the surface of the soil,which affects the adhesion between Gram-negative bacteria and soil samples and occupies the pore of the soil.In addition,it may also be blocked by the release of gas from gram negative bacteria.