Study On Raw Water Quality Characteristics And Conventional Treatment Process Effect Of Qujiang Water Plant In Xi'an

Water resource is an important part of urban water supply system, and the quality condition closely relates to supply security. Because quality information shows strong real-time characteristic, it is necessary to analyze water quality situation and variation tendency regularly for scientific basis to process adjustment. Meanwhile, based on the water quality situation, ability of conventional process should be analyzed for identifying potential security risk.In the paper, the water quality situation,change tendency,seasonal variation characteristics and traditional process character of Qujiang water plant are analyzed, and the main research contents and conclusions can be divided into three parts.1) Water quality Assessment(1) The raw water quality of Qujiang water plant belongs to Class I, and CODcr, CODmn, NH3-N, TN and TP are the main evaluation factors.(2) Compared to standard index method and comprehensive evaluation method, fuzzy evaluation model basing on Principal Component Analysis, which weakens the problem of subjectivity and information overlap during traditional assessment, is more suitable for the assessment of micro-polluted sourceand plant raw water.2) The division of water quality and variation tendency Analysis(1) Raw water quality shows three or two different stages in one year. As the three stages, the first stage is from January to June, the second stage is from July to September, and the last stage is from October to December. As the two stages, one is from January to June; the other is from July to December. CODmn is the main characteristic parameter to distinguish different stages. From January to June, the index is slightly low, and from July to September, the index is slightly high. It should be attention that seasonal quality mutations may occur during July to September.(2) Except CODmn, which shows increasing trend and concentration variance is 0.137 mg/(L-a), other indexes change smoothly. It can be seen that the raw water quality of Qujiang water plant is good, but organic pollution risk exists.3) Analysis of conventional process ability(1) The removal rate of CODmn in conventional water treatment process is about 22.1%-61.3%, and the average rate is 38.3%. Coagulation and sedimentation is the key link, which contributes about 43%-68% to CODmn, and filtration unit takes the low removal rate, which is only about 10%.(2) Temperature can influence remove of CODmn strongly. The experiences of practical operation indicate that the best temperature to remove is 20-30℃, and because of affecting coagulation and sedimentation, temperature being too high or too low will both decrease the removal rate of CODmn.(3) Amount of coagulant is one of the most important facts to remove CODmn. Based the practical operation, it can be realized that, as dosing quantity is 5-20mg/L, The removal rate of CODmn in conventional water treatment process is about 20%-30%, as dosing quantity is more than 20mg/L, the removal rate is about 60%-70% and will not change significantly.(4) The conventional water treatment process can remove TP efficiently, and the removal rate, which may change as seasonal variation, is 60%-90%. The removal rate of TP in coagulation sedimentationunit and filtration unit is relatively high, which is 25%-77%and 40%-76% respectively, and the average rate is almost the same.