| With the development of urbanization and social economy at the top speed,the leakage of pollutants especially organic contaminants leads to the severe contamination of groundwater and human's drinking water is seriously threatened.Aniline is applied widely and generally pollutes groundwater,which is a common raw material in modern agricultural,medical and chemical products.Owing to its toxicity,carcinogenicity,mutagenicity and persistent properties in environment,prevention and remediation of aniline contamination for groundwater has aroused widespread public attention.Among the groundwater remediation techniques,in situ bioremediation has significant advantages for removing organic pollutants.Because it is more cost-effective,environmentally friendly and available for federated application with other methods,compared with physical and chemical remediation techniques which have high capital and operating costs or potential production of secondary pollutants.Bioaugmentation by using biodegradative activities of indigenous or introduced microorganisms can shorten remediation time and increase remediation efficiency.However,bioaugmentation is prone to failure because the activity and biomass of introduced microorganisms decrease shortly after adding them to the contaminated sites.So the survival and transport of introduced degrading bacteria in complex subsurface ecosystems is the key to successful bioaugmentation.This study focused on exploring the relationship of bacterial survival,bacterial transport and bioaugmentation efficiency to offer theoretical basis to actual in situ bioremediation of aniline-contaminated groundwater.The previous studies show that Pseudomonas migulae AN-1 is psychrotrophic and has high efficacy of aniline biodegradation.Its degrading efficiency and optimal degradation conditions at low temperatures have been investigated.However,its survival,transport and remediation efficiency in aniline-contaminated aquifer are still unclear.In this study,the characteristics of Pseudomonas migulae AN-1 related to its survival and transport in aquifer were investigated.A novel system of combining GFP tagging and light transmission was established to visually investigate the transport of AN-1 in aquifer.It noninvasive captured both adhered and planktonic bacteria transport for the first time.The pathway and mechanism of AN-1 transport were intuitively explored to definite and adjust remediation regions.It has guiding meaning for denifiting remediation region and enhancing bioremediation.Saponins were used to enhance AN-1 transport in stimulated aquifer.The promotion function was explained by surface thermodynamic properties,interfacial surface tensions,Gibbs energy,and the DLVO interaction energy of the system composed of AN-1,liquid and sand.It has guidance on enhancing bioremediation and relieving bioclogging.Survival,transport and remediation efficiency of AN-1 in aniline-contaminated aquifer were investigated and verified to form a technical architecture of in situ bioaugmentation of aniline-contaminated aquifer.Above were meaningful to the actural bioremediation.The main conclusions of this study are as follows:? The characteristics of AN-1 related to its survival and transport in aquiferAN-1 is able to automatically adjust its cellular membrane permeability,hydrophobicity and autoaggregation to adapt the variation of aniline and promote aniline biodegradation.When the aniline concentration <100 mg L-1,AN-1 exhibited moderated hydrophobic and its cellular membrane permeability increased.When the aniline concentration ?100 mg L-1,AN-1 was strong hydrophobic and its cellular membrane permeability was invariable.Besides,AN-1 has a capability of forming biofilms.Its biofilms have well aniline degrading efficacy and high resistance to aniline shock.Ca2+ promoted biofilm formation by AN-1,Fe2+ inhibited formation,and SO42-had enhancement when its concentration was above ?5 m M.? The mechanism of AN-1 transport in aquiferThe mechanism of AN-1 transport in aquifer was visually and quantitatively explored by combining GFP tagging and light transmission method.Both free-state and retained AN-1 in simulated aquifer were noninvasively captured at the same time.Bacterial biocharacteristics and convection-dispersion of groundwater have together functions on bacterial transport,which is influenced by biological and hydrogeological factors.(1)The velocity of AN-1 transport: AN-1 transported faster than groundwater.The finer the media were,the greater the enhancement of bacterial velocity.(2)The possibility of AN-1 transport: With the increasing granular size,groundwater flow rate,dissolved organic matter concentration and decreasing ion strength,mass recovery of AN-1 was raised and deposition rate coefficient was reduced.AN-1 tended to transport.With the same ion strength and anion,the divalent cation played a greater inhibition role than the monovalent cation.With the same ion strength and cation,AN-1 transport was restrained more significantly with the monovalent anion than the divalent anion.(3)The dynamics of AN-1 transport: The initial shape of bacterial plume in medium and coarse sand after injection was a narrow strip along the injection well and an ellipsoid in the lower part of the injection well,respectively.The relationship of bacterial plume areas and time was linear.And the area carrying AN-1 in medium sand was larger than that in coarse sand under the same conditions(the same injection volume,the same period and the same flow rate).A continuous biological zone can be formed from the injection well to the front of bacterial plume,including planktonic bacterial plume zone and bacteria-adhered zone behind the plume.It has guiding meaning for denifiting remediation region and enhancing bioremediation.? The enhancement of AN-1 transport in aquifer:Saponins have negligible toxicity on AN-1.The aniline degradation rate and biomass with 0.1%,0.3% or 0.5% saponins added were a little greater than without saponins.0.1% was the optimal concentration of saponin solution for flushing.Under the concentration of 0.1% saponins,interfacial surface tensions and Gibbs energy of the system(AN-1-liquid-sand)were the smallest,and the adherence of AN-1 to the sand was the greatest.Washing with 0.1% saponins was the most cost-effective to promote AN-1 transport in aquifer,which is to use 0.1% saponins to flush after AN-1 inoculation into the aquifer without pretreation.The second transport was realized to expand the potential remediation regions.Ions had few effects on the enhancement of AN-1 transport by saponins.When saponins and ions coexisted,saponins significantly increased the engery barrier between AN-1 and sand grains comparing with ions exiting alone.Saponins eliminated the inhibition by ions and realized the promotion on AN-1 transport in saturated porous media.? Bioremediation of simulated aniline-contaminated aquifer by AN-1:AN-1 survived with high aniline biodegrading efficiency in simulated aniline-contaminated aquifer.Bioaugmentation with AN-1 could shift microbial community structures to adapt to the shock of aniline and prevent the inhibition of indigenous bacteria by aniline.A biological treatment zone for bioremediation can be formed from the injection well to the front of bacterial plume.When AN-1 was inoculated in the pollutant plume,abundant degrading bacteria accumulated nearby downstream orientation of the injection well.This accumulation zone of AN-1 played the main role of biodegradation with great degrading rate and might form bioclogging potentially.This zone migrated and expanded downstream slowly.Some planktonic cells peeled off from the sands or biofilm matrixes and transported with water flow.AN-1 had great bioremediation efficiency of aniline-contaminated aquifer.The innovations of this study are as follows: A novel system of combining GFP tagging and light transmission was established to visually investigate the transport of degrading bacteria in simulated aquifer.It noninvasively captured both adhered and planktonic bacteria transport at the same time and intuitively demonstrated the effective bioremediation regions for the first time;A novel technique of enhancing degrading bacteria transport in aquifer and its promotion mechanism were investigated,which was more cost-effective and environmentally friendly;Survival,transport and bioremediation efficacy of the aniline-degrading bacterium,Pseudomonas migulae AN-1,was firstly verified to illuminate the relationship of bacterial survival,bacterial transport and bioaugmentation efficiency.Above all,this study is meaningful to actural bioremediation of aniline-contaminated groundwater and lays theoretical foundations for actual engineering application. |
PDF Full Text Request