Research On Dynamic Comprehensive Evaluation Method Of Water Quality And Application

Making water quality evaluation can describe water state objectively and quantitatively, and can also provide foundation in treating and researching water environment. However, there are many factors in influencing water environmental quality. Those factors often correlate with each other and always changing along with time and space. Therefore, water environmental quality is not only objective but also fuzzy variable. In other words, water environmental quality is multifactor influenced and comprehensive affected. At present, there are always discussion in ensure the index weight of water quality evaluation. Many assessments haven’t combined the study of temporal and spatial distribution of pollutants with the continuous dynamics comprehensive water quality evaluation together; moreover, those assessments often ignored the errors which were emerged in collecting and analyzing water sample. All those problems caused that there is still not a unified water quality evaluation model as yet.This paper making continuous and dynamic water quality evaluate in biliu reservoir and put forward corresponding treatment counter measures. The next are the main results:(1) It could improve the model’s computational efficiency by using normalization formula when solving dimensionless and negative index problems; determining the direction of eigenvector by means of analyzing the6conditions of eigenvector which may emerged in principal component made the model results more reasonable.(2) According to analysis of the index weight’s different meanings in evaluation target and objectimproved the variable fuzzy recognition method for water quality evaluation which is based on the modified AHP-PCA, the index weight not only contains the original water quality data but also merges scientific researchers’recognition, which makes it more reasonable; As an interval, the evaluate result of this method reflects the variability and fuzziness of water quality, and its rationality has been verified by comparing with the results of comprehensive index method and modified comprehensive index method. The water quality example simulated by Monte Carlo method shows that random errors could affect the evaluate results obviously.(3) The dynamic evaluation results of the Biliu reservoir showed that water quality was good enough to be a water source in the mass, which was between the second kind of water and the third. The reservoir water quality didn’t have significant differences between layers and months. The exceeding standard indexes were TN and DO (in summer). DO was mainly influenced by the temperature variation which was caused by seasonal change, and had the thermocline phenomenon. TN was mainly influenced by rainfall and runoff. A lot of pollutants got in the reservoir with the rainfall before flood season which caused the increasing of TN. Many of those pollutants got out of the reservoir with the runoff in flood season. Finally, the accumulation of pollutants after flood season would decrease TN in the reservoir. The high background value in the basin was a reason for the high TN in the reservoir. A variety of pollutants which deposited in the bottom of the reservoir in suspended state and deposited state played a role as a pollutants reservoir in the migration and transformation process of TN. Those pollutants would release N into the reservoir under certain condition and increased the water load.(4) The evaluation results of Biliu reservoir showed that TN, TP and DO were the most important indexes, and their weight was determined as0.280,0.326and0.155respectively. Eutrophication was the main problem in Biliu reservoir. Affected by point source pollution, non-point source pollution and inner pollution, the water environmental capacity of TN was surpassed the allowed capacity, the water environmental capacity of TP less than the allowed capacity. Therefore, decreasing TN input and controlling TP input is necessary for improving the water quality. According to the analysis of pollution sources, the paper put forward that pollution treatment should comprehensively considered point source pollution, non-point source pollution and inner pollution. In addition, enhancing water quality monitoring capacity and perfecting the management system can improve water quality in reservoir from engineering and non-engineering aspects and guarantee the safety of using water. Finally, the paper point out the deficiency and problems in researching so that the author could do further study conveniently.