Objective To evaluate the water quality and identify influencing factors of ultra-filtration devices to protect drinking water safety of students.
Methods Twenty-five watert reatment devices were randomly selected from 12 primary and 10 secondary schools in a district of Shanghai to collect direct drinking water samples in February and October 2014.The quality of direct drinking water samples was evaluated by Water Quality Index (WQI),and the improvement of water quality was evaluated by comparing WQI between treated water and source water.The elimination rate of chemical oxygen demand was utilized for the ability of water purification.Binary logistic model was applied to analyze the influencing factors of water quality improvement.
Results The 25 ultra-filtration devices all used tap water from the municipal network water supply as the source water.The qualified rate of 50 direct drinking water samples was 80%,and the main unqualified indicators were total number of colonies and zinc.There was no significant difference in WQI of the direct drinking water samples (0.374& #177;0.100) and tap water samples (0.392& #177;0.027)(t=1.26,P=0.22).The WQI based on organic pollution index of the direct drinking water samples (0.084& #177;0.039) was significantly lower than that of tap water samples (0.122& #177;0.024)(t=5.78,P=0.00).The improved rate of water quality was 74%,and most organic pollution indices were improved.Low using frequency (water consumption < 50 L/d) and unqualified water purification ability (elimination rate of chemical oxygen demand < 25%) were the main influencing factors contributing to quality deterioration of direct drinking water.
Conclusion Ultra-filtration devices in the selected schools can control organic pollution in direct drinking water,but hygienic issues are also identified which are influenced by several factors.
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