Measuring method of chemical oxygen demand (COD) of ultrahigh-chlorine wastewater

Abstract

The invention provides a simple efficient pretreatment method for shielding chlorine ion interference, which can perform mass determination and has the characteristic of wide application range. The method is suitable for determining the chemical oxygen demand (CDO) of wastewater in which the chlorine ion concentration is less than 20000 mg/L and the COD is greater than 20 mg/L. The measuring method comprises the following steps: 1. measuring the chlorine ion concentration in a wastewater sample by silver nitrate titrimetry (GB/T 11896-1989), and preparing a water solution with the same chlorine ion concentration as the wastewater sample as a quality control water sample or taking added standard recovery quality control measures; 2. respectively taking the wastewater sample and quality control water sample, mixing with equal volume of a mercuric sulfate solution, carrying out pretreatment (innovative point), and standing for some time until the chlorine ions and mercury ions form a stable mercury tetrachloride complex, thereby shielding the chlorine ions in wastewater; and 3. transferring the pretreated water sample in the step 2 into a prefabricated test tube, and carrying out an SM5220D process to obtain the measuring result of COD.

Description

technical field [0001] The present invention relates to an assay method. Background technique [0002] With the increasing development of industry and economic construction, the water bodies of rivers, lakes and seas in our country are increasingly polluted by organic matter. The organic matter consumes a large amount of dissolved oxygen in the water body during the biodegradation process, resulting in the disappearance of oxygen, destroying the ecological balance, and polluting the environment. have very serious effects. Due to the complex composition of organic matter, it is very difficult to determine the content of various organic matter separately. Some comprehensive indicators are often used to replace the concentration of organic pollutants. Among them, chemical oxygen demand (COD) is a comprehensive indicator that is widely used, and it is also one of the very important items in water quality monitoring. Therefore, the correct determination of chemical oxygen deman...

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Problems solved by technology

However, the interference of chlorides coexisting in wastewater on the measured value of chemical oxygen demand has always been a difficult problem to solve.

The wastewater produced in many fields contains chloride ions, such as: chemical wastewater, waste treatment plant wastewater, sodium hydrochloride wastewater, wastewater from bleaching process, dye production salting-out wastewater, industrial wastewater using seawater, etc., in which the concentration of chloride ions is basically in the More than 1000mg / L, the current wastewater similar to that of garbage treatment plants can even reach hundreds of thousands of mg per liter, and because the wastewater treatment process of garbage treatment plants is a process similar to liquid concentration, as time continues to prolong, chloride ions in wastewater The content will be higher and higher, which will seriously interfere with the determination of chemical oxygen demand, especially for wastewater with high / ultra-high chloride ion and low chemical oxygen demand, it is even more difficult to obtain accurate measurement results, and then The detection of chemical oxygen demand in wastewater has brought insurmountable obstacles, and it is also a difficulty faced by many third-party testing agencies. Therefore, accurate and effective COD measurement methods have broad application prospects.

[0004] Whether it is the addition of mercuric sulfate solids in the GB 11914-89 standard to complex chloride ions before measurement, or the chlorine gas calibration method in the HJ / T70-2001 standard, there are respective shortcomings: the first method requires adding a large amount of sulfuric acid and Mercury sulfate causes great pollution to the environment, and the detection cost also increases accordingly; the second method is cumbersome and prone to errors, and is not suitable for the measurement of a large number of water samples

[0009] 1. The COD value obtained by using the chlorine gas calibration curve and simulating the high chlorine environment of wastewater has a large deviation

[0010] 2. The highest capacity to treat wastewater with a chloride ion concentration of 10,000mg / L, the determination of high / ultra-high (chloride ion concentration reaches more than 100,000 mg / L) requires large multiple dilution, resulting in large errors

[0011] 3. The measurement methods with high accuracy are difficult to measure in batches or the measurement process is too cumbersome

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