| Objective The monitoring results of centralized water supply quality in Qixia District of Nanjing City from 2009 to 2018 were analyzed to understand the current status of drinking water quality and factors of affecting water quality,to find out the root causes of drinking water quality,to propose corresponding countermeasures and suggestions,to provide a scientific basis for strengthening the management of centralized water supply units,and to further ensure the health and sanitation of drinking water for residents in Qixia District.Method In the past ten years,factory water and terminal water of 12(9 existing,3closed)centralized water supply units have been tested for water quality during 2009-2018.Epidata3.1 is used to establish a database,and SPSS17.0 is used for statistical analysis,comparing the difference of the qualification rate between the water samples by?~2text,using the U test to analyze the difference of some indicators of different types of water samples,using H test to analyze the differences of some indicators of multiple groups of water samples,Finally,the model was established by Logistic regression model to further prove the factors of affecting water quality.P<0.05 was considered statistically significant.Result In 2009-2018,the total water quality qualified rate was from 66.40%to 86.67%,and the difference between the years was statistically significant(χ~2=91.786,P<0.05).In 2009-2018,the total qualified rate of municipal waterworks was 95.53%,which was higher than that of township waterworks which is 76.18%.There was a statistical difference between them(χ~2=54.044,P<0.05).The top three indicators which affect water quality are turbidity,visible to the naked eye,and total number of colonies.The water quality qualified rate was statistically different among different seasons(raining season,dry season,and lever period)(χ~2=38.071,P<0.05),the highest qualified rate is the dry season,followed by the lever period,the lowest qualified rate is the raining season.The qualified rate of water quality treated with different disinfectants was statistically significant(χ~2=57.013,P<0.05).The relatively high qualified rates were in the liquid chlorine group and the sodium hypochlorite group,and the relatively low pass rates were in the chlorine dioxide group and the bleach powder group.There are 14 items of indicator which are statistically significant between the township waterworks and the municipal waterworks,they are Total coliforms,heat-resistant coliforms,total colonies,turbidity,Smell and taste,visible to the naked eye,p H,aluminum,iron,sulfate,total dissolved solids,total hardness,oxygen consumption,free residual chlorine.The H test was carried out on the indicators of water samples at different seasons.The results showed that there were 17 indicators with statistical differences:total coliform,heat-resistant coliform,total number of colonies,turbidity,smell and taste,Macroscopically visible,iron,aluminum,free residual chlorine terminal water,p H,sulfate,total dissolved solids,total hardness,oxygen consumption,ammonia nitrogen,zinc,nitrate.The Total number of colonies,turbidity,odor and taste,macroscopic objects,the value of aluminum,total dissolved solids,total hardness,oxygen consumption,ammonia nitrogen,total coliforms,heat-resistant coliforms,and sulfates during raining seasons were relatively high.The statistical analysis results showed that the value of total coliform,heat-resistant coliform,total number of colonies,smell and taste,visible to the naked eye,oxygen consumption were different statistically under different disinfectant treatments.Effect of microbial indicators control:the effect of the liquid chlorine group is the best,followed by the sodium hypochlorite group;in the control of sensory traits and general chemical indicators,most of the indicators in the sodium hypochlorite group have lower detection values,followed by the liquid chlorine group.According to the binary Logistic regression analysis,the probability of unqualified water quality in the township waterworks is 7.037 times that of the municipal water plant.The water quality in the dry season is relatively safe,followed by the flat period,the qualified rate of water quality in the raining season is the lowest.Chlorine dioxide and bleaching powder are the factors leading to a decline in qualified rate of water quality.Conclusions In 2009-2018,the qualified rate of the water quality in Qixia District has been improved,especially in township waterworks.The qualified rate of municipal waterworks is much higher than that of township waterworks.The top three indicators which affect water quality are turbidity,visible to the naked eye,and total number of colonies.The lowest qualified rate of the water quality is during the raining seasons,the highest is during the dry seasons.Sodium hypochlorite and liquid chlorine are relatively suitable disinfectants. |
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