| Recently,the extensive use and even abuse of antibiotics have been leading a steady increase of antibiotic residues in aquatic environment.The consequent emergence of a variety of antibiotic resistant bacteria and antibiotic resistance genes directly threaten drinking water quality.The existing treatment technology of urban water works cannot effectively remove antibiotic resistance bacteria and antibiotic resistance genes from water,and may even increase their contents after treatment or distribution.In this study,we investigate the effect of filtration process on antibiotic-resistant bacteria removal during water supply treatment.We applied various operation conditions to reveal the profiles of antibiotic resistant bacteria,including filtration material thickness,hydraulic residence time,filter size and disinfection pretreatment and other operating conditions.The dynamics of four antibiotic resistant bacteria,including tetracycline(TET),norfloxacin(NOR),sulfamoxazole(SUL)and clindamycin(CLI)were investigated,and the main conclusions were drawn as follows:Firstly,the thickness of quartz sand filter significantly influenced the numbers of four types of antibiotic-resistant bacteria either in filtered water or on filter.When the thickness of quartz sand filter material increased from 1 cm to 5 cm,the numbers of four types of antibiotic-resistant bacteria in water decreased gradually,while the four types of antibiotic-resistant bacteria in the filter material showed an upward trend.For example,the numbers of tetracycline,norfloxacin,sulfonamides and clindamycin resistant bacteria in the discharged water decreased by 64%,56%,64% and 65%,respectively,after being filtered for 80 min by the quartz sand filter material with the particle size of0.3 mm.At the same time,the numbers of resistant bacteria on the filter material increased by 64%,42%,28% and 23%.At the same time,it was found that the numbers of four types of antibiotic-resistant bacteria in the water and the filter material changed more obviously under the condition of adding disinfection pretreatment before filtration.At the same time,the numbers of four types of antibiotic-resistant bacteria in the water decreased by 71%-88%,and the numbers of antibiotic-resistant bacteria in the filter material increased by 36%-68%.Secondly,the residence time of the quartz sand filter material significantly influenced the numbers of four types of antibiotic-resistant bacteria either in filtered water or on filter.When the filtration residence time of the quartz sand filter material increased from0 min to 80 min,the numbers of four types of antibiotic-resistant bacteria in water decreased gradually,while the four types of antibiotic-resistant bacteria in the filter material showed an upward trend.For example,the numbers of tetracycline,norfloxacin,sulfonamides and clindamycin resistant bacteria decreased by 53%,54%,45% and 34%,respectively,after being filtered by a quartz sand filter with a particle size of 0.3 mm and a thickness of 3 cm.At the same time,the numbers of resistant bacteria on the filter material increased by 46%,7%,26% and 9% compared with the residence time of 0min.At the same time,it was found that disinfection pretreatment before filtration could also improve the treatment effect.Under the same filtration treatment conditions,the numbers of four types of resistant bacteria decreased by 47%-73%,while the numbers of resistant bacteria remaining on the filter material increased by 16%-48% compared with the residence time of 0 min.Thirdly,the particle size of the quartz sand filter material significantly influenced the numbers of four types of antibiotic-resistant bacteria either in filtered water or on filter.When the particle size of the quartz sand filter material increased from 0.3 mm to 6 mm,the numbers of the four types of antibiotic-resistant bacteria in water increased gradually,while the four types of antibiotic-resistant bacteria in the filter material showed a decreasing trend.For example,the numbers of tetracycline,norfloxacin,sulfonamides and clindamycin resistant bacteria increased by 64%,49%,44% and 46%,respectively,after80 min filtration with quartz sand filter material of 5 cm thickness.At the same time,the numbers of resistant bacteria on the filter material decreased by 24%,9%,13% and 12%compared with the size of 0.3 mm.At the same time,it was found that disinfection pretreatment before filtration could improve the treatment effect.Under the same filtration treatment conditions,the number of four types of resistant bacteria per 100 mL of effluent water increased by 33%-78%.However,the number of resistant bacteria on the filter material decreased by 31%-39% compared with that on the filter material with the particle size of 0.3 mm.Fourthly,statistical analysis results show that adjusting the thickness and particle size of quartz sand during filtration is more beneficial to the removal of TET and the retention of CLI filter material.The removal of SUL and CLI and the retention of TET filter material are better by adjusting the thickness and residence time of quartz sand.The removal effect of NOR and the retention effect of filter material are the best when the thickness of quartz sand is adjusted.Adjust the particle size of quartz sand is more conducive to the retention of SUL filter material.The removal of TET and NOR was better by adjusting the thickness of quartz sand during pretreatment and filtration.The removal of SUL and CLI is better by adjusting the thickness of quartz sand and the residence time of filter material.Adjust the thickness and particle size of quartz sand to the four types of antibiotic resistant bacteria filter material retention effect is the best.In addition,the removal effect of pretreatment-filtration linkage process is more significant than that of filtration process,and different kinds of antibiotic-resistant bacteria are suitable for different filtration conditions. |
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