Researches Into Water Quality Safety Assessment Of Drinking Water Sources In Small Towns

At first, the thesis introduces the statue of researches at home and abroad into security assessment on quality of drinking water sources. Combined with the actual situation of China's small cities and towns, it puts forward the problems that need further settling in course of water quality assessment in small cities and towns. Through the analysis and research of safety of water quality, the thesis discusses the connotation which safety of water quality should contains. The level of safety of water quality relies on three indexes which include category of water quality, level of eutrophication, the risk level of water quality.By means of the investigation and a series of analysis on water quality monitoring data, eight critical factors which have an important impact on water quality of water sources in small towns are found out. Eight factors which involve in are as follows:nitrogen, phosphorus, potassium permanganate index, biochemical oxygen demand of five days, volatile phenol, petroleum, dissolved oxygen, fecal coliform bacteria. On this basis, through analysis and comparison of current water quality evaluation methods which commonly used, it is arrived that conbined with single-factor evaluation, integrated pollution index method can better evaluate water quality categories. According to the relevant information and analysis and comparison of advantages and disadvantages of common eutrophication assessment method, a comprehensive nutritional index method is made use of as a primary means of eutrophication assessment, other methods for supporting evaluation. Because quantitative evaluation of the risk of water quality is more credible, considering the actual fact, quantitative evaluation of the risk of water quality is adopted.Based on the connotation of safety of water quality, assessment system established includes three evaluation indexes. Due to lack of sufficient knowledge of the risk of water quality at present, the weight of the risk of water quality is difficult to decide in course of assessment of safety of water quality, the water quality risk is not involved in water quality safety evaluation, only as a reference index. By choosing AHP to determine the weight of the water quality categories and the level of eutrophication, the membership of water quality categories and the level of eutrophication are calculated first, and then the membership of overall water quality safety levels is worked out. At last, based on the principle of maximum degree of membership, water quality safety level is determined.Based on the data in 2008 of a reservoir of Shandong Province, assessment of water quality safety as to the reservoir is made in the paper. The membership of water quality safety which it corresponds to is 0.7558. The results show that the reservoir as water sources are safe. But because the risk probability that it's total nitrogen, total phosphorus, potassium permanganate index exceed the normal value is high, there are certain threaten to water quality safety.