[Change of drinking water quality in Shijiazhuang South-to-North Water Diversion area from 2014 to 2021].

Abstract

Objective: To analyze the change of drinking water quality in the receiving area of Shijiazhuang South-to-North Water Transfer Project.

Methods: 2029 monitoring data of drinking water in the receiving areas of the South-to-North Water Transfer Project in Shijiazhuang from 2014 to 2021 were collected and collated according to the Sanitary Standard for Drinking Water(GB 5749-2006). Off-work water and pipe water before and after the total coliform group of South-to-North Water Transfer Project, heat-resistant coliform bacteria, escherichia coli, the total number of colonies, arsenic, cadmium, chromium, lead, mercury, nitrate, fluoride, selenium, cyanide, chloroform, carbon tetrachloride, chromaticity and turbidity, odor and taste, visible to the naked eye, pH, aluminum, iron, manganese, copper, zinc, chloride, sulfate, total soluble solids, total hardness, oxygen consumption, volatile phenols, anionic synthetic detergent, ammonia nitrogen, residual chlorine and chlorine dioxide were evaluated and compared. χ~2 test was used to compare the qualified rate, Mann-Whitney rank sum test was used to compare the test values of each index, and simple superposition comprehensive water environmental quality index method was used to evaluate the water quality comprehensively.

Results: Before the South-to-North Water Transfer Project, the total qualified rate of drinking water was 84.21%, that of factory water was 81.29%, and that of end water was 85.97%. The total qualified rate of drinking water after the South-to-North Water Transfer Project was 98.72%, that of factory water was 98.89%, and that of end water was 98.66%. The total qualified rate of water quality, the qualified rate of factory water and the qualified rate of end water after the South-to-North water transfer were higher than those before the transfer(P<0.05). The qualified rates of microbial indexes and total hardness of ex-factory water before the South-to-North Water Transfer Project were 94.37% and 89.94%, and those of microbial indexes and total hardness of end water were 94.32% and 93.35%, respectively. After the South-to-North Water Transfer, the qualified rates of microbial indexes and total hardness of the ex-factory water were 100.00% and 98.90%, and the qualified rates of microbial indexes and total hardness of the end water were 100.00% and 99.24%, respectively. After the South-to-North water transfer, the qualified rate of microbial indexes and total hardness of factory water and peripheral water were higher than those before the transfer(P<0.05). After the South-to-North Water Transfer, the M of total coliform group, total colony number, total hardness, fluoride, nitrate nitrogen, chloride, sulfate and dissolved total solids were lower than those before water transfer(For example, the median number of colonies and total hardness of factory water before the South-to-North Water Transfer were 20.00 CFU/100 mL and 248.00 mg/L, respectively. After the South-to-North Water Transfer, the median number of colonies and total hardness were 1.00 CFU/100 mL and 129.00 mg/L, respectively), while the M of trichloromethane, aluminum, pH and oxygen consumption were higher than those before water transfer(For example, the median of trichloromethane and aluminum before the South-to-North Water Transfer is 0.04×10~(-2) and 0.04×10~(-1) mg/L, respectively. After the South-to-North Water Transfer, the median of chloroform and aluminum were 0.06×10~(-2) and 0.25×10~(-1) mg/L, respectively)(P<0.05). The median WQI of comprehensive water environmental quality index before and after the South-to-North Water Transfer was 4.58 and 2.37(P<0.05), respectively.

Conclusion: The introduction of the South-to-North Water Transfer has significantly improved the quality of drinking water in Shijiazhuang city. Microbial contamination and total hardness exceedance have been greatly improved.