Regulation And Mechanism Of Deposition And Transport Behavior Of Enterococcus Faecalis In Activated Carbon

In recent years,along with the development of society and the improvement of living standards,people’s requirements for drinking water quality have been continuously improved.Activated carbon as the most commonly used adsorbent which having a wide range of sources and low cost,is used by countries around the world for advanced treatment of drinking water.There are a large number of pathogenic microorganisms in livestock manure,hospital sewage,residential wastewater,septic tank sewage and garbage dumps.The random discharge of these sewage pollutants and the flow of surface runoff after being washed by rain caused many surface water sources to be polluted,which brought great potential threat to drinking water safety and endangered people’s health.In this paper,the common pathogen of pollution in the water environment,Enterococcus faecalis,is used as the research goal.The column experiment is designed to explore the effects of various physical,chemical,and biological factors on its migration,which plays an important role in ensuring the safety of drinking water and ensuring people’s health.Granular activated carbon was used as the filling medium for the column experiment to simulate the water environment of the activated carbon filter.The column experiment studys the effect of different granular activated carbon particle size on the migration of Enterococcus faecalis.The results showed that the particle size of1.0-2.0 mm（median particle size of 1.5 mm）was most suitable.Then the effects of non-water flow rate,ionic strength and ion species,activated carbon shape and biofilm on the migration of Enterococcus faecalis were studied.The results of this study as follows:（1）When granular activated carbon with a median particle size of 0.8 mm is used as the filling medium,the migration of Enterococcus faecalis in the column experiment shows a surface blocking phenomenon.And the plateau value of the breakthrough curve increases as the particle size of activated carbon increases.Due to the increase in particle size,the specific surface area is relatively reduced and the adsorption sites can be provided less.At the same time,since the deformability of the bacterial colloid decreases with the increase of the particle size,the deposition amount of Enterococcus faecalis continuously decreases.（2）The increasing flow rate of water flow causes the loss rate of Enterococcus faecalis to increase continuously.That is,the outflow ratio of the penetration curve of Enterococcus faecalis increases with the flow rate of water flow.When The flow velocity of the water is increased,the shear force of the faecal cocci colloid deposited on the surface of the granular activated carbon is continuously increased.Therefore,the bacterial colloid is easily discharged by the water flow and the deposition amount is reduced.According to the theory of colloidal filtration,when the collection efficiency of the single collector does not change,the collision times of the bacterial colloid and the medium particles are less.Besides the adhesion efficiency of the bacterial colloid is reduced at a higher flow rate.（3）Increasing the ionic strength of the solution and injecting Ca²⁺can increase the deposition of Enterococcus faecalis in granular activated carbon.The ionic strength can affect the electric double layer of the bacterial colloid.When the ionic strength is increasing,the thickness of the electric double layer of the bacterial colloid is reduced.It can reduce the repulsive force between bacteria-bacteria and bacteria-medium particles and makes the bacteria more easily deposited on the carbon particles.In the solution of the same ionic strength,the blocking effect of divalent Ca²⁺on the bacterial colloid is stronger than that of the monovalent Na⁺.Thus the deposition of Enterococcus faecalis in the background solution is larger in the CaCl₂ solution.（4）The migration ability of Enterococcus faecalis in columnar activated carbon is greater than that of granular activated carbon.The main reason is that the columnar activated carbon has a small specific surface area.The adsorption space provided for the Enterococcus faecalis is reduced.The Enterococcus faecalis has a small deposition amount in the columnar activated carbon and the penetration curve is also high.（5）The deposition effect of Enterococcus faecalis in the bioparticle activated carbon column is better than that of the granular activated carbon column.The surface of the biofilm is mainly composed of EPS.The interaction between the extracellular polymer EPS-Enterococcus faecalis and the surface characteristics of EPS enhance the deposition of Enterococcus faecalis in the biological granular activated carbon.The biological granular activated carbon used is prepared by Enterococcus faecalis,which makes the adsorption of Enterococcus faecalis more easily by itself.