| Because of the aggravation of the pollution in drinking water source area and the worsening of the ageing problem in city pipe networks,the biosecurity of water distribution system became a serious problem of drinking water.The increase of organic content accelerated the growth of microbes and consumed residual chlorine rapidly and then sharply woke the biological stability of drinking water.In order to prevent the deterioration of the water quality,researches tried to enhanced disinfection process by increasing dosage of conventional disinfectants（e.g.,chlorine,chlorine dioxide,or ozone）to restrain the microbial growth.Although the method can prevent the disinfection decaying,it generated disinfection byproducts（DBP）and caused the increase of microbial resistance.On the other side the critical requirement of drinking water restricted the use of new types of disinfectants（e.g.,biocides,antibiotics,and novel bactericidal metallic nanomaterials）for their potential（eco）toxicological impacts on the biosafety.Differed from these researches,this study focused on limiting the concentration of nutrient element in water resources to guarantee the biological stability.And phosphorus was chosen as the essential nutrient element to control microbial growth in stead of the assimilable organic carbon（AOC）,providing more choices to ensure the biological stability.To solve the difficulty of dealing with low concentration phosphate,this study chose lanthanum-based adsorbents in numerous adsorption materials because of its most effective ability to suppress microbial growth by reducing low level of phosphate.Through electrospinning and a subsequent in situ surfactant-free precipitation method,La（OH）3 nanorods and La2O3 nanoparticles firmly immobilized and well dispersed in polyacrylonitrile（PAN）Nanofibers were fabricated for the first time.Moreover,the study adjusted and controled the parameters of electrospinning to gain the ideal material owing sustainable structure,consistent morphology,small diameter.Through the process of electrospinning,the immobilization by PAN nanofibers effectively facilitated the in situ formation of the well-dispersed La-based nanostructures,and thus the electrospinning and in situ precipitation method together rendered better structural integrity and higher phosphate removal efficiency due to more exposed active sites for binding phosphate.Among thses methods,PAN fibers acted as a nanoreactor,which could not only used as support structure and provided a place for the reaction between La3+ and alkali solution,but also impact the nucleation and growth process of the assemblies to avoid the forming of agglomeration.The great adsorption capacity of La2O3/PAN and La（OH）3/PAN nanofibers confirmed the strong binding between lanthanum and phosphate.The maximum phosphate adsorption capacity（qm）of La2O3/PAN was 77.76 mg P/g（La）,while La（OH）3/PAN can thus be 172.2 mg P/g（La）due to the highly well dispersed La（OH）3 active sites in the nanofibers.Moreover,a fast kinetics and high-removal efficiency were observed for the adsorption of low concentration phosphate（2 mg/L）within 20 min,owning to the high activity of our materials,which can result in a stringent phosphate deficient condition to kill microorganism in water effectively.Besides,because the in-situ encapsulation by PAN nanofibers can avoid lanthanum leakage,the material presented excellent biosecurity for holding water stability in practical application.The antibacterial study showed that the growth of both grampositive bacteria and gram-negative bacteria were inhibited when the concentration of phosphate in the solution was controlled under certain level.Furthermore,the test in fresh tap water demonstrated the biological stability for applying these antibacterial methods.The number of total bacteria did not increase after the recontamination in the phosphate starvation situation.At last,new nanofibrous membrane（La（OH）3/PAN）was fabricated.The nanofibrous membrane could synchronously kill out existing bacteria immediately and scavenge phosphate-nutrition against microbe regrowth over a long time.The increase of conductivity by adding salt made the diameter of the nanofiber sharply decrease and then the pore size of membrane was also declined.Simultaneously,the salt provided a positive charge on the membrane surface,protecting the membrane being adhered by microbe.The enhancement of the mechanical property of the membrane was attributed to the in-situ precipitation.These characteristics reinforced the capability of membrane rejection.Hence,an antibacterial strategy with both immediate bacterial removal to decrease the amount of cells and persistent antibacteria to control the regrowth in drinking water supplies was succeeded through the membrane filtration. |
