Construction And Application Of Black And Odor Warning Method For Urban Water Body

Urban black and odorous water body has the characteristics of low dissolved oxygen（DO）and oxidation-reduction potential（ORP）,high concentration of organic matter and ammonia nitrogen（NH₃-N）,etc.,which is usually accompanied by blackening and peculiar smell of water body,which has adverse effects on human settlement environment and river ecosystem.At present,there is still the risk of black and smelly river treatment in urban black and smelly river.The construction of early warning method is beneficial to early warning of black and smelly recurrence and effectively reduce the environmental impact of black and smelly water body.As an important means in the long-term guarantee mechanism,it is particularly important to carry out the research on the early warning method of black odor,which covers the screening of early warning indicators and the classification of early warning levels.In this paper,the critical value experiment of the black and odor proces of the water body,the screen experiment of the black and odor warning index and the microbial community change experiment of the black and odor process of the wat body are carried out by simulating the black and odor water body,the chemical oxygen demand（COD）is determined as the boundary condition index of the black and odor water body,the ORP and the DO are determined as the black and odor characterization indexes,the black and odor warning method is constructed by dividing the warning grades and adopting the Shape-based BS algorithm,Meanwhile,comprehensive chemical index method and biological index evaluation method were used to evaluate the risk of black and odor water.The experimental conclusions are as follows:（1）Determination of critical conditions for black and smelly water.Organic matter and ammonia nitrogen are the key water quality indicators that indirectly lead to black and smelly water.Assuming that COD and NH₃-N are critical conditions of black odor,the correlation between COD,NH₃-N and black odor of water body was studied by experiments,and the verification study was carried out.The results showed that the sensitivity of NH₃-N to ORP and DO was low,and it was not suitable to be used as early warning index.COD has a strong correlation with ORP and DO.With the increase of COD concentration,the risk of black and smelly water increases,and the degree of black and smelly water is more obvious,which can be used as a critical index for black and smelly water warning.When COD was less than 30 mg/L,the black and smelly water would not occur.When COD>52 mg/L,black odor will occur in the water body.When 30 mg/L<COD<52 mg/L,the water body may be black and smelly or not,depending on other environmental conditions,which is also the core threshold of black and smelly warning.Therefore,30 and 52 mg/L are determined as the lower and upper critical COD concentrations.（2）Screening experiment of black and odor warning index.The changes of ammonia-nitrogen,p H,temperature,microbial community,ORP and DO during the black-odor process were studied.p H and temperature did not change significantly before and after black odor,so they were not suitable as early warning indicators;The significant change of key dominant microbial community in the process of black and odor water can be used as the basis of black and odor warning,but it is not suitable as a warning index because of the high cost and long period of sampling.ORP as a process monitoring parameter is more accurate and easy to measure,in the water,under certain conditions,it is the leading indicator of water quality changes,can play a very good early warning function,so it is suitable for early warning indicators;DO can be used as an auxiliary warning index to make the black odor warning more accurate.（3）Construction and application of black and odor early warning method.Firstly,an index system was established,in which COD was taken as the boundary condition index of black and smelly water,and ORP and DO were taken as the characteristic indexes of black and smelly water.The warning level of water black and odor is divided into red warning and orange warning,and the corresponding water black and odor degree is severe black and odor and mild black and odor respectively;According to the method,a black odor early warning method is constructed through a Shape-based BS algorithm in change-point detection,ORP and DO curves in a critical region are collected,different trend characteristic curves are formed into a curve library,curves drawn by real-time monitoring data are compared,and early warning is effectively carried out by predicting the trend,so that countermeasures are taken in advance,adverse effects of environmental deterioration on people’s lives are reduced,treatment difficulty is reduced,and treatment cost is reduced.（4）Risk safety assessment of black and smelly water body.The comprehensive chemical index method and biological index evaluation method were used to analyze the changes of different COD concentrations and main microbial communities.It was concluded that the COD concentration and the main microbial communities affecting black odor should be controlled to reduce the risk of black odor.Combined with the black odor warning method,the risk safety assessment of black odor in water body was realized.