Study On Microbial Risk Assessment And Control Technology In Water Purification Process

The safety of microorganism directly affects human health.The primary task of drinking water treatment is to ensure the safety of microorganism in water supply system.The microbiological safety of different water purification processes in a city in the south of China was evaluated to master the current situation of microbiological safety and identify the directories of disinfectant-resistant bacteria.In addition,the growth characteristics,control technology and chlorine-resistant mechanism of chlorine-resistant bacteria were studied.First of all,high-throughput sequencing technologies was used to study the microbiological diversities of effluents of different processes,filter sand and biological activated carbon in the conventional treatment process,ozone and biological activated carbon(O3-BAC)advanced treatment process and biological activated carbon-ultrafiltration(BAC-UF)combined process.In the meantime,the total plate count and the total heterotrophic bacteria count(HPC)were measured in the effluents from every processes.The results showed that the total plate count and the total heterotrophic bacteria count(HPC)in finished water of three water plants met the national standard and U.S Environmental Protection Agency(EPA)standard,the diversity and abundance of microbes in raw water could be reduced by all three water treatment processes,in which the removal efficiencies from high to low were the BAC-UF combined process,the O3-BAC advanced treatment process and the conventional treatment process respectively.Specifically,microorganism could be removed by the ozone,ultrafiltration and disinfection units in a great degree.However,microbial leak could be easily caused by the BAC unit,which is the major risk source of microbial outbreak in the water treatment process.The dominant phyla in the water treatment process were Proteobacteria,Actinomycetes,Cyanobacteria,Firmicutes,and Planctomycetacia separately.A large number of Sphinx,Bacillus,Mycobacterium,Pseudomonas and Acinetobacter that belong to chlorine-resistant bacteria were detected in the finished water.Moreover,Mycobacterium and Acinetobacter are conditioned pathogen,and Sphinx and Pseudomonas can cause pipeline corrosion,which should be taken seriously.Secondly,the effects on three chlorine-resistant bacteria strains were researched by temperature,pH,water quality and residual chlorine.The results indicated that three chlorine resistant bacteria strains could multiply rapidly under the condition of 25?~35?of temperature,6~8 of pH and raw water quality.Furthermore,the numbers of bacteria in the coagulating sedimentation and sand filter effluents could be reduced to some degree,but not be removed thoroughly.Besides,the inactivation rates of two bacillus strains by the sodium hypochlorite,chloramine and chlorine dioxide within the specified concentration were less than three logarithmic degrees,and resistance to chlorine degree of the spores were higher than the cells.The inactivation rate of Lysinibacillus fusiformis spores was just 1.3 logarithmic degrees by 4.0 mg/L of free chlorine dosage,and resistance to chlorine degree of Lysinibacillus fusiformis was the highest.Finally,ultraviolet ray and ozone disinfection technologies were employed to inactivate Lysinibacillus fusiformis.The results presented that the activation rates of Lysinibacillus fusiformis spores be higher than three logarithmic degrees under the condition of 2 mg/L of ozone dosage with 12 min of disinfecting time and 120 mJ/cm~2 of ultraviolet ray dosage.In addition,the activation mechanism of Lysinibacillus fusiformis by ozone and ultraviolet ray were analyzed.Thereinto,ozone destroyed the cell structure of Lysinibacillus fusiformis to lead to intracellular materials leak to kill it.Whereas ultraviolet ray could penetrate the cell membrane and cytoplasm of Lysinibacillus fusiformis to destroy the nucleic acid,which made DNA not duplicate itself,to achieve the purpose of sterilization.