| Chemical Oxygen Demand?COD?is an important indicator to reflect the degree of pollution caused by reducing substances in monitored water quality,and also an important reference for water quality monitoring and evaluation.Usually,namely into the water with chemical method to add antioxidant,under certain conditions,the oxidation of 1 liter of reducing the amount of material consumed antioxidant convert into 1 liter are all the required amount of oxygen after oxidation,expressed in mg/L.This index is usually used to represent the comprehensive organic pollution degree of water body and has been widely used in Marine ecological environment quality evaluation and eutrophication research.However,in low salinity of estuarine and coastal coast,potassium dichromate method and the determination of permanganate index were affected by salinity?the chloride ion concentration?interference,measurement can not accurately reflect the low salinity sea coastal organic pollution degree,so close to the coast tidal river COD determination method of study will help to accurately reflect the status of organic pollution in the region,for roots as the core of pollution control measures are put forward and solutions.Based on the monitoring of tidal reach of the Yellow River delta this section as the research object,analysis from 2012 to 2016 water quality monitoring index of the year and interannual variation law and its relationship with the tides and salinity,explore the salinity?the chloride ion concentration?for CODCr,potassium permanganate index and the influence of water COD determination results.Through the field take the water of the sea river estuary and determination of parameters such as PH,salinity,conductivity,and COD,with actual water dilution and join glucose as a substrate for laboratory simulated tidal river water quality characteristics,using potassium dichromate method,the method and the determination of permanganate index,water COD determination method of three different monitoring methods,analyzes the effect of salinity for the determination of three methods,and puts forward certain salinity tidal range is suitable for the monitoring results of correction formula.Finally established suitable for tidal river COD monitoring method of wate quality,and connecting with the typical tidal river,river,the fairy ditch dongying city site data of monitoring results of water quality analysis and validation of the formula.It provides a basis for the determination of COD in the tidal reach and further water quality evaluation.The main conclusions of this paper are as follows:?1?Most of the coastal sea tide in Dongying develops in 34 month and 711months,the tide phenomenon of the water can make the mixed each other rivers and the sea sea,at the same time,greatly increase the salinity of the estuary of tidal action,so that the concentration of chloride in water quality monitoring with the tide has come in and a significant rise.From 2012 to 2016,a typical tidal flow in the cross section of the monitoring of water quality of dissolved oxygen,ammonia nitrogen and potassium permanganate index annual averages are basic can meet the national V class water quality standards,and CODCr in average higher V class water quality standard,standard appear unstable situation.The results of monitoring results showed that there was a good correlation between the chloride concentration of water and the monitoring results of CODCr.?2?Within the range of 0‰7‰of salinity,the measured value of CODCr by potassium dichromate method does not change with the increase of salinity,tends to be stable and is not disturbed by salinity factors.In the range of salinity ranging from7‰to 25‰,COD value increased logarithmically with salinity increasing.In the range of salinity ranging from 25‰to 35‰,COD value increased with salinity.Therefore,the salinity of 7‰is defined as the critical value of the measurement of COD by potassium dichromate.If the salinity is higher than this value,it is not suitable for monitoring by this method.Seawater COD determination method in about25‰35‰salinity range is not affected by salinity change,basic and 0‰25‰salinity range of determination results obviously on the low side,and with the increase of salinity increases,therefore,will be in the water salinity 25 per thousand defined as seawater salinity threshold of determination method of COD,lower than this value,unfavorable use this method to monitor.The determination of permanganate index is within the range of 0‰10‰of salinity,which is not affected by the change of chloride ion concentration and is relatively stable.Within the range of 10‰35‰of salinity,the measured value increases logarithmically with the increase of salinity.Therefore,the salinity of 10‰in water samples is defined as the salinity critical value of the method for the determination of permanganate index.?3?The CODCr monitoring value within the range of 7‰25‰of salinity has a good correlation with salinity.This salinity range is selected for correction and the correction formula is proposed.Different concentration of glucose solution of potassium dichromate method difference between measured and the theoretical value and salinity multiple linear fitting,7‰25‰salinity range standard potassium dichromate method for COD determination results of correction formula:C0=-b-?b2-4ac?1/2/2aAmong them,a=3.573×10-3·d-7.104×10-3,b=-8.968×10-2·d-0.8.22,c=COD-11.14·d-21.14,d=In?S+0.0109?Where S is the measured salinity of water samples;COD is CODCr measured value;C0 is the corrected value.The formula is applied to the area of salinity of the tidal river in the river of the Yellow River delta,and the calibration of the COD determination results of standard dichromate method.The monitoring value of permanganate index within the range of 25‰35‰of salinity has a good correlation with salinity.Solutions of different concentrations of glucose difference between measured and theoretical value of permanganate index with multiple linear fitting,salinity 25‰35‰salinity range standard correction formula for the results of determination of permanganate index:C1=-b-?b2-4ac?1/2/2aAmong them,a=-1.415×10-4·d×10-4, b=-3.838×10-3·d-0.9930,c=COD-1.135d-2.525, d=In?S+0.0012?Where S is the measured salinity of water sample,COD is the measured value,and C1 is the corrected value.?4?the school official of the Yellow River delta,2012-2017 typical challenges on tidal river and the fairy ditch COD monitoring section measured after correction,the correction after success rate can be increased by 10%50%,the standard level significantly increased,decreased by the COD determination method for effects of salinity.In 2017,COD monitoring results of the cantilever river have been corrected and basically meet the water quality requirements of class V in the national surface water environmental quality standard.Finally,established the Yellow River delta tidal rivers of COD determination to salinity as a method to choose the basis,7‰salinity and 25‰respectively as the critical point of measurement method to choose the optimal monitoring method.Salinity of 0‰7‰was determined by potassium dichromate method.Within the range of salinity ranging from 7‰to 25‰,the results were corrected using the correction formula 4-5 in this paper after the determination by potassium dichromate method.25‰35‰salinity range,using the method of determination of permanganate index determination by formula 4-10 after correction,or water COD determination method is used to monitor directly,adopt the corresponding standards for water quality evaluation. |
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