River water environmental quality assessment based on improved fuzzy mathematics

In recent years,with the rapid development of China′s economy and the gradual progress of urbanization,urban industrial and agricultural wastewater,waste liquids,and domestic sewage have been continuously discharged into rivers,which have made the problem of water pollution increasingly worse.A large number of river water bodies have been severely polluted due to eutrophication and water inactivation.The original ecological balance of the water bodies has been destroyed,the ecological environment quality of river water has declined sharply,and even major water pollution accidents that endanger human health have occurred.Quantitative or qualitative evaluation of river water quality elements can provide a scientific basis for subsequent river water pollution control and water environmental protection.Eight evaluation indicators are selected from 14 monitoring sections of the Daqing River from 2014 to 2016 and a combination of improved fuzzy mathematics method and singlefactor evaluation method is used to conduct comprehensive water environment quality evaluation. The traditional fuzzy mathematics method is to construct the fuzzy factor set which is not easy to determine the degree of pros and cons,then establish the evaluation set and the membership function according to the water quality evaluation standard,obtain the weight and the degree of membership to quantify.Finally,the two complex operations are performed to obtain the river [JP2]water quality level based on the principle of maximum membership.This operation is effective in evaluating the general river water environment,but it cannot evaluate the inferior Class V water quality,nor can it obtain water quality indicators that play a major[JP] role in river water quality.Therefore,this research first improves the fuzzy mathematics method and then combines the single-factor evaluation method to obtain the water environment quality evaluation and main pollution indicators of the Daqing River. The results show that in 2014 and 2015,the sections that did not meet the standards of Class V functional zone in the GB-3838[KG-*2]–[KG-*3]2002 Environmental quality standards for surface water were Xingaifang,Wangting,Matou,Jiaozhuang and Anzhou sections,accounting for 35.7% of the monitored sections of that year.In 2016,the sections that did not meet the standards were wharf sections,accounting for 7.14% of the monitored sections of that year.Among them,ammonia nitrogen and total phosphorus were the main pollution factors of the monitored sections.The ammonia nitrogen exceeded the standard by an average of 6.78 times,and the peak appeared at the Wangting section in 2014,which was as high as 10.9 times;the total phosphorus exceeded the standard by an average of 3.51 times,and the peak appeared at the Anzhou section in 2014,which was up to 4.53 times.In addition,in 2014,the chemical oxygen demand of Xingaifang,Matou,and Jiaozhuang sections all slightly exceeded the standard,but their exceeding multiples were all less than 1.2 times.The relative calculated values of dissolved oxygen,permanganate index,five day biochemical oxygen demand,total lead,and petroleum products did not exceed 1.0,all of which met the water environmental quality requirements of Class V functional zones.The water quality of the monitored sections from 2014 to 2015 showed a downward trend,but the water quality category did not change significantly,while the water quality improved significantly in 2016;ammonia nitrogen and total phosphorus were the main influencing factors.Water pollution in the study area is within a controllable range,and subsequent monitoring of pollution sources in key river basins needs to be strengthened to effectively protect the water environment in a timely manner;enterprises or farms that require sewage discharge must be strictly supervised in the river basin and the wastewater must be recycled in a harmless manner.The discharge of domestic sewage and disposal of domestic garbage should be strictly controlled,and direct discharge into rivers should be prohibited. The combination of improved fuzzy mathematics method and singlefactor evaluation method can better solve the problem of fuzzy water pollution that is difficult to quantify.It can not only avoid the influence of human factors and reflect the water environment quality under the joint influence of multiple factors,but also determine the main pollutant categories that affect the water environment quality evaluation results.

Project Supported:

Clc Number: