| Evaluation of drinking water security is one of the most crucial techniques in water management in context of the rapid urbanization, especially for the backup water sources under the increasing water pollution incidents during the past decade. The purpose of this study is to provide a assessment method for water quality safety management in backup water source. The strategies of worldwide drinking water safety management policy, and methods of major factor analysis, water security evaluation were reviewed. The pollution share rate method and principal component analysis (PCA) were adopted to identify the main pollution source, and an integrated approach combining the water quality index evaluation, acute toxicity risk assessment and species sensitivity distributions (SSDs) methods were developed to evaluate the water security of backup water source. Five typical backup water source in Hangzhou as case study were then used to test the feasibility of the proposed water safety evaluation method. The main research conclusions are as follows:(1) The combined pollution share rate method and principal component analysis could effectively identify the pollution sources of backup water source. Based on a four-year monitoring record for the five studied backup water source, the pollution share rate of 109 indicators were compared to screen 16 main pollution factors, the sum of which was higher than 90% (i.e. TN, TP, BOD5, DO, petroleum, COD, pH, ammonium nitrogen, fluoride, potassium permanganate index, iron, manganese, fecal coliform, volatile phenol, anionic synthetic detergent and mercury); and the strong related indicator of the first principal component were then validated by the principal component analysis. The results showed that the primary pollution factor for all the five backup water sources is TN, with a much higher pollution share rates (15.61% -38.48%) than other indicators (0.46% -18.73%); the ammonia nitrogen, TN, TP are the major pollution indicators, with all the factor loading rates above 0.75.(2) The spatio-temporal variation of the major pollution indicators could be explained by correlation analysis within the SPSS software. The correlation between water quality and water seasons, watersheds were analysis by Spearman correlation analysis of SPSS 18. The correlation matrix between months and water quality depicts the temporal change of water quality, while the matrix between locations and water quality indicates the spatial variations. The results showed that the TN concentrations in dry seasons were higher than the wet season, and Xi’angang had the highest TN concentrations while Shanhusha had the best water quality; The DO concentrations in normal season and wet period were respectively 5.78±2.36 mg/L,5.26±1.55 mg/L, and no significant influence was observed for water season; concentration of TP, ammonia nitrogen and potassium permanganate in the wet period were 0.23+0.10 mg/L,2.62±1.27 mg/L and 6.21±1.04 mg/L, respectively, all of which are higher than in dry seasons.(3) The integrated approach combining water quality index evaluation, acute toxicity risk assessment and species sensitivity distributions methods could evaluate the water satefy condition of backup water sources. The calculation results by CCME-WQI methods indicated that the Xiangang of Tiaoxi watershed had the lowest WQI score with values ranged from 52.4 to 78.8, among which the water security level in 2012 and 2013 were poor; and the WQI score of other four backup water source ranged from 70.5 to 91.9, which were in the satefy level of fair and good. The toxicity threshold of nitrate nitrogen and ammonia nitrogen were tested by the photobacteria method. The results demonstrated that the EC50 of luminescent bacteria for nitrate nitrogen and ammonia nitrogen were 35.45 g L-1 、 3.28 g L-1, respectively, indicating that the nitrate nitrogen and ammonia nitrogen of the five backup water sources had no acute toxicity to the aquatic organisms. The species sensitivity distributions assessment results for the primary pollution factor TN on 139 senstive species revealed that the potentially affected fraction (PAF) of Sanbaitan, Tieshahe, Shanhusha and Xi’angang were higher than 5%, indicating high risk to aquatic ecosystem. The highest risk occurred in Xi’angang with a PAF value of 15.77%, which highlighted the importance of nitrogen management in water satety protection.The results will provide a scientific basis for pollution prevention measures and management decisions of backup water source in Hangzhou. |
PDF Full Text Request