| Microorganisms in the reclaimed water adhere to pipe walls during distribution and gradually form biofilms.And some microorganisms that are harmful to human may regenerate and multiply in biofilms.Researches have shown that biofilms can simultaneously promote the diffusion and acquisition of antibiotic resistance,increasing the probability of pathogenic microorganisms acquiring resistance.This experiment used three self-made AR reactors as simulation devices to simulate the real inner environment of three different reclaimed water pipelines in the lab.The growth laws of biofilm in the pipelines,microbial structure in the biofilms and the distribution of antibiotic resistance genes in the simulation devices were studied.The result of this study can be a guidance for clarifying the growth laws of microorganisms on the inner surface of reclaimed water transport and distribution pipelines and the species category of the microorganisms that are prone to breed in the biofilms.Specific engineering measures to ensure the safety of reclaimed water effect may also be taken on the basic of this study.The main conclusions of this study are as follows:(1)The result of HPCs and EPS concentration showed: The biomass of heterotrophic bacteria in the biofilm on the surface of cast iron coupons was the highest,and in general it was increasing with time.While the biomass of heterotrophic bacteria in the biofilm on the surface of stainless steel coupons was the lowest,and it increased first and then decreased.The trend of biomass of heterotrophic bacteria in the biofilm on the surface of PE was the same as on 304 stainless steel coupons.During the first 30 days,biomass on PE coupons was greater than the other two kind of coupons.Among the three,cast iron coupon had the highest concentration of polysaccharide in the biofilm.And no protein was detected on the surface of these two kinds of coupons.(2)The result of antibiotic resistance bacteria counting showed: The biomass of tetracycline-and streptomycin-resistant bacteria were less in biofilms,while ampicillin-and chloramphenicol-resistant bacteria were relatively higher abundant.The environment in biofilms on PE coupons was more suitable for ampicillin-resistant bacteria and chloramphenicol-resistant bacteria.(3)The microbial compositions in biofilms on the surface of coupons were different from that in the raw water.And that on stainless steel and PE coupons had higher similarity with that in raw water,while between cast iron and raw water the similarity was relatively low.The dominant microbial composition in biofilms on cast iron coupons changed greatly over time.: On the 30 th day,the most abundant phylum,and class were Firmicutes and Clostridia,respectively.While on the 60 th day were Proteobacteria and Gammaproteobacteria.And on 90 th day,Proteobacteria,and Alphaproteobacteria were most abundant.On stainless steel coupons surface,the dominant microbial composition in biofilms did not change much: The most abundant phylum,and class were Proteobacteria and Alphaproteobacteria respectively on the 60 th day.And on the 90 th day were Proteobacteria and Alphaproteobacteria.On PE coupons surface,the dominant microbial composition in biofilms did not change much,either.On both 60 th and 90 th day,the most abundant phylum and class were Proteobacteria,and Alphaproteobacteria.(4)The comparision on retention rate between three simulation devices showed: The total retention rate of ARGs by the three devices all showed an upward trend over time.The retention rate of tetracycline ARGs in the device with cast iron and PE coupons increased,while it decreased in the device with stainless steel coupons.The retention rates of sulfonamides ARGs in all three devices showed an upward trend over time.The comparision of ARGs concentration on three kinds of coupons showed: The total abundance of ARGs in biofilms on cast iron coupons gradually increased over time,while on stainless steel and PE coupons first increased and then decreased,and on stainless steel coupons had a larger changing range.Sulfonamides ARGs accounted for the highest proportion in biofilms,followed by tetracyclines ARGs.(5)Both in reclaimed water and biofilm,the total abundance of ARGs had a significant positive correlation with 16 s DNA.Most of ARGs in reclaimed water had a significant positive correlation with the total biomass,especially tetracyclines ARGs;while in the biofilm the correlation was weak,and only bla Amp C1 and sul2 had significant positive correlations with 16 s DNA(P <0.01),and flo R showed a positive correlation(P <0.05).Most of the target ARGs and int I2 had some correlation,but there were fewer ARGs relating with int I1.Analysis of the correlation between 18 ARGs in reclaimed water and biofilm suggests that there was a clear correlation between the same type and different types of ARGs,but the correlation was weaker in biofilms than in reclaimed water.It was found that erm F,sul1,and tet W had significant positive correlations with several genus at the same time,while TRA3-20,Hydrogenophaga,Ensifer,Mycobacterium,Brevundimonas and Phascolarctobacterium had significant positive correlations with several ARGs. |
