| The supply of urban drinking water is one of the most important works, as it is not only a major social security problem, but also one of the major livelihood issues of science and technology to be solved, proposed by the National Twelfth Five Year Plan of science and technology and technological development. With the rapid development of social ecology, agricultural non-point source pollution in the eastern region of China is serious, and water quality in the area is of high organic matter, high ammonia nitrogen and high algae, which has become a main threat for the safety of drinking water in villages and towns. From the source water to the tap, microorganisms are always present in the potable water transportation system. Biological safety problem is more easily to be a potential risk of drinking water because of its hidden nature.In this research, the temporal and spatial distribution of microbial community in the drinking water treatment system and drinking water distribution system was studied. The dynamic change of microbial community was investigated. The risk of microbial safety in drinking water supply system was evaluated by using the common opportunistic pathogenic bacteria in water. The main results are as follows:â…°) The biological stability of drinking water and the spatial and temporal distribution of microbial community in different drinking water treatment processes were explored.Treated water quality, treated by biological pre treatment, treatment of conventional treatment and advanced treatment process, is stable and meets the drinking water standard. However, the treated water had the potential problem of biological instability and the treatment process for organic matter, especially assimilable organic carbon (AOC) removal needs further improvement. The number of microbial species in biofilms was significantly more than that in water. The nitrifiers including Nitrospira and Nitrosomonas typically existed in biological oxidation pond with abundance of 10-20% and 2% respectively. There is high abundance of Cyanobacteria (more than 25%) in sedimentation tank. The microbial community diversity level was the lowest in ozone contact reactor. The genera of Pseudomonas and Sphingomonas had higher proportion (7-10%) in output water. The number of microbial species was significantly more in summer than in winter. Proteobacteria, Cyanobacteria, Bacteroidetes and Actinobacteria were the most dominant phyla, accounting for 33%,20%,15% and 12%, respectively in winter, while the abundance of the Bacteroidetes significantly decreased to 3% in summer. Purpureocillium was the unique dominant eukaryotic microorganism in winter with the abundance of 85%, while Davidiella, Alternaria, Phoma, Leptosphaerulina and Purpureocillium were all accounted for a certain proportion (3%-5%) in summer, which made the eukaryotic microorganisms more various.â…±) The temporal and spatial distribution of bacterial community in biofilm at the start and the end of drinking water network was investigated.The bacteria quantity in biofilms located in the start and the end of DWDS did not differ greatly. The total number of bacteria and HPC in both locations ranged from 107 to 109 cells/cm2 and from 105 to 106 CFU/cm2. The composition of bacterial community in biofilms located in the start and the end of DWDS had difference. The dominant bacterial genera in biofilm located in the start of DWDS, in descending order of relative abundance, were Flavobacterium (6.22%), Comamonas (5.38%), Alishewanella (5.03%), Gemmatimonas (3.75%) and Delftia (2.54%), while the dominant bacterial genera in biofilm located in the end of DWDS were Acinetobacter (7.75%), Hyphomicrobium (4.47%), Pseudomonas (2.00%) and Stenotrophomonas (1.95%). The total bacterial density reached to stable number of 107-109 cells/cm2 in relatively short period of time (<1 year). The bacterial community in biofilm gradually succeeded with time. As pipe age increased, HPC increased from 105 to 106 CFU/cm2 and the RNA transcript level increased from 105 to 107 copies/cm2. Furthermore, Alphaproteobacteria gradually became the dominant species with the abundance from 30% to 66%. Coliform, Salmonella and Shigella could breed in biofilms with the maximum density of up to 104 CFU/cm2. The detection rate of opportunistic pathogens in biofilm in the start of network was 44%, which was higher than that in the end of network with 22%, and the number and detection rate of opportunistic pathogens in biofilms increased with pipe age.â…²) The radial-space distribution of bacteria community in biofilm along pipe wall of large-diameter pipes in the drinking water distribution system was investigated.The biofilm density, TS and VS content increased gradually from the upside to the bottom along the pipe wall. The biomass in biofilms was concentrated in the upside and bottom of the pipe wall, and the number of bacteria in both areas was accounted for more than 80% of the total amount in the pipe wall. The total number of bacteria and HPC in both locations ranged from 106 to 108 cells/cm2 and from 105 to 107CFU/cm2, which is obviously 10-100 times more than that in the middle of pipe wall. Compared with the upside and bottom of the pipe wall, the structure of bacterial community in the middle was distributed evenly, and the bacterial community diversity level was the highest. More than 20 genera, including Pseudomonas, Sphingomonas, Hyphomicrobium, was accounted for more than 1% of the bacteria in biofilm in the middle of pipe wall. A variety of pathogenic bacteria, including Escherichia coli, Staphylococcus epidermidis and et al. were detected in biofilm. The abundance of Escherichia coli was 1.39%, which was the most among the detecred pathogens. The detection rate of Escherichia coli was 100% among all samples. Compared with the upside and bottom of the pipe wall, the abundance of pathogen was the highest in the middle of pipe wall. |
