A Study On Rapid POU Water Disinfection Materials Base On The Silver Nanoparticle

According to World Health Organization(WHO),roughly 2 million people,mostly children under the age of 5,die annually from diarrhea due to the lack of safe drinking water.In addition,more than 660 million people do not have access to safe drinking water,530million of which are in rural areas.Water treatment technologies,especially point-of-use(POU)drinking water disinfection technologies that fit resource limited situations are urgently needed.Among them,silver nanoparticle(Ag NP)decorated materials as POU water disinfectants have received extensive attention all around the world.In this paper,the preparation methods and characteristics of the two kinds of novel POU bactericidal materials based on the good bactericidal effect of Ag NP were reported in detail.(1)Ag NPs decorated chitosan(CS)cryogels have been fabricated through a simple freeze-drying process for point-of-use(POU)water disinfection application.The CS/Ag NPs cryogels showed high porosity,good mechanical property,excellent water absorption capability,and most importantly,efficient bactericidal feature.The absorption capacity for water was found to be 47 g/g,and about 90%of which could be recovered by simple squeezing.Three different sizes of Ag NPs were compared regarding their bactericidal capability to both E.coli and B.subtilis.At optimum conditions,a 3 log reduction of bacteria was observed by holding the bacterial suspension(10~8 colony forming units(cfu)/m L)in the cryogels for 5min,with the silver content of only 7.5 mg/g in the cryogels.It could be further increased to a4 log reduction when doubling the contact time.Furthermore,the total Ag in processed water was found to be only 22?g/L,half of the safety limit set by China(<50?g/L).The bactericidal effectiveness of the material for real surface water samples was also demonstrated by treating water samples with different water quality matrices,including lake water and sewage water samples.In all the three lake water samples treated,both the total bacteria and E.coli met the regulations for drinking water in China(<100 cfu/m L for total bacteria and negative for E.coli).The CS/Ag NPs cryogels are thought to work for drinking water disinfection in disaster relief and contingency water supply applications.(2)Porous chitosan(CS)membrane coated filter paper loading Ag NPs(CFPA)was formed for POU water disinfection.By controlling the amount of CS,the flow rate and bactericidal effect of filter paper can be adjusted,so that it can be applied to water with different water quality matrixes.When the CS content increased from 0.5 to 2.0 wt%,the flow rate of CFPA would change from 9.3 to 0.53 L/min/m~2,and the bactericidal effect against E.coli and B.subtilis could improve from 4 and 3.6 to 4.9 and 4.8 log reduction,respectively.Furthermore,because of the existence of CS membrane,the tensile strength of the CFPA in wet condition is 1.8 MPa,8 times as much as that without CS.In addition,Ag NPs loading in CS membrane can be greatly boosted without worrying about the excessive release of Ag into treated water,thereby significantly improve the bactericidal efficiency.At optimum condition,the total Ag in treated water by CFPA was below 45?g/L,only 1/10 of Ag NPs loaded filter paper without CS,half of the drinking water standard of China(<50?g/L).Real surface water samples were used for the demonstration of the bactericidal performance of the CFPA,and the results showed both the total bacterial and E.coli counts are far below the WHO standard.In this study,the two materials were proved to have good practical use performance.However,it was also found in this study that the factors such as organic matter,inorganic matter and turbidity in the actual water samples may affect the bactericidal properties of the materials.Based on this,studying the influence degree and mechanism of different water quality parameters on materials is of great significance for improving the practical application performance of these materials.And this is a complex and systematic work.However,in this study,I only discovered this problem and carried on the preliminary research and analysis but did not systematically study and analyze the influence degree and influence mechanism of each parameter.Therefore,this will be the most important research direction for further research on this material in the future.