Mechanism Of Virus-colloid Cotransport In Saturated/Unsaturated Porous Media

Pathogenic contaminants can directly cause the spread of human diseases,which pose a great risk to human health.Pathogenic contaminants enter surface water bodies and groundwater systems through precipitation,snow melting and irrigation,thus causing soil and groundwater pollution.The presence of natural colloids affects the transport behavior of contaminants through porous media.Therefore,it is of great significance to explore the transport of pathogenic contaminants in porous media in the presence of natural colloids for the assessment of the health risk of groundwater and the remediation of water pollution by pathogenic contaminants.To investigate the role of colloids in the transport of virus through porous media,a series of experiments were performed using columns packed with sand.The Escherichia coli phage(E.coli phage)was used as the model virus.Silica and humic acid as the model colloid in this study.It provides useful reference for protecting groundwater source from pathogenic contaminants pollution and evaluating the risk of pathogenic contaminants in the presence of colloid in groundwater.The main conclusions of this study as follows:1.Properties of virus-colloid suspensionThe inactivation of viruses in the presence of colloid and properties of virus-colloid suspension was studied in batch experiments.Batch experiments in the presence of colloid indicated that no significant virus inactivation was expected under the present experimental conditions.Results indicated that the hydrodynamic size was 513.4 nm when the concentration of silica was 10mg/L.And there was only one peak,which suggested the aggregation of virus-silica particles in mixed suspension.The hydrodynamic size was 692.5 nm when the silica concentration in the suspension increased to 20 mg/L.This implied that increasing the silica concentration results in a higher binding capacity of the virus.The zeta potential values ranged from-26.13 mV to-27.83 mV as the silica concentration in the suspension increased from 10 to 20 mg/L.The silica concentration was observed to exhibit a negligible effect on the zeta potential of the virus-silica system.The absolute zeta potential of the particles was <30 mV and the aggregated particles were in an unsteady state condition.Results indicated that the hydrodynamic size was 439.87 nm when the concentration of humic acid was 10mg/L and the zeta potential value was-52.3 mV.This suggested the aggregation of virus-humic acid particles in mixed suspension.The hydrodynamic size was 454.95 nm when the silica concentration in the suspension increased to 20 mg/L and the zeta potential value was-56.7 mV.With the increased of the concentration of humic acid,the particle size of the mixed suspension increased.This showed that the increased humic acid concentration formed large amount of aggregation particles due to collision between viruses and humic acid particles.It can be seen from the results that the stability of virus-humic acid system was higher than that of virus-silica system.The reason should be related to the morphology difference of silica and humic acid.Silica was spherical with smooth surface,while humic acid was shuttle type with rough surface.At the same time,there were a large number of functional groups on the surface of the humic acid,which was easier to combine with the virus into relatively stable aggregation particles.Therefore,the stability of the humic acid virus suspension was stronger than that of the silica virus suspension.2.The roles of colloid played in virus transport through saturated porous mediaIn this part,we mainly discuss the transport of virus in saturated porous media in the presence of silica and humic acid.Silica and humic acid showed different effects on virus transport under the same experiment conditions and test methods.Results demonstrated that silica hindered virus transport and humic acid facilitated virus transport in the presence of saturated porous media.For the virus-silica experiment shows that with the increase of silica concentration from 10 mg/L to 20 mg/L,the mass recovery of virus changed from 47.13% to 41.43%.The experiment results indicated that with the increase of the concentration of silica,the mass recovery of virus decreased.Virus exhibited a higher degree of retention in the presence of silica.The virus-silica aggregation particles were the mainly particles in transport process under saturated condition.This could be related to pore structure changes caused by aggregated virus-silica particles located within the pores of the sand.It can be seen from the experiment results that the presence of humic acid can facilitate the transport of virus in porous media.The virus-silica experiment showed the mass recovery of virus was 45.46% when the silica concentration was 10 mg/L.And the mass recovery of virus was 31.63% when the silica concentration was 20 mg/L.Compared with the individual transport of virus in saturated condition,humic acid can promote the transport of virus.According to the properties of virus-humic acid system,the aggregated particles were relatively stable.Humic acid acted as a carrier with a strong migration ability which can promote the transport of virus in saturated porous media.When the concentration of humic acid increased,humic acid carried more virus particles and moved out of saturated sand column with water flow.Therefore,humic acid facilitated virus transport in the presence of saturated porous media.3.The roles of colloid played in virus transport through unsaturated porous mediaExperiments show that both silica and humic acid facilitated virus transport in the presence of unsaturated porous media.However,the influence factors of the two colloids on the virus are different.For silica-virus transport experiment,capillary forces were stronger than the virus-silica interactions and inhibited the aggregation of particles.Suspended silica competes with the virus for sorption sites because of a high affinity for the air water interface.The occupation of retention sites by silica at the air-water interface during the early stages of injection in the unsaturated column experiments inhibits virus retention.This may because silica inhibits virus retention by electrostatic repulsion of like-charged particles,and concomitantly facilitates virus transport under unsaturated conditions.For the cotransport of humic acid-virus,humic acid promoted virus transport under unsaturated conditions.From the analysis of the potential and particle size of the mixed suspension,it indicated that the humic acid-virus aggregation particles were relatively stable.This may due to the strong interaction between the aggregated particles.Humic acid had a strong migration ability.When humic acid and virus formed aggregation particles,it will increase the migration ability of virus in unsaturated sand column and promoted the transport of virus.