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CN-122017126-A - Method for accurately and rapidly determining COD in high-chlorine wastewater

CN122017126ACN 122017126 ACN122017126 ACN 122017126ACN-122017126-A

Abstract

The invention relates to the technical field of sewage detection, and discloses a method for accurately and rapidly determining COD in high-chlorine wastewater, which comprises the steps of preparing a solution, sampling, adding a masking agent, performing vibration complexing, performing oxidation, catalyzing, performing reflux digestion, performing titration determination, performing calculation, wherein the detection range of the method is wider, the concentration interference range of a chlorine example is increased from 1000 to 40100 mg/L, the detection limit is increased from 20 to 15.9 mg/L, the accuracy is better than that of a national standard, the nitrogen stripping is faster, a plurality of batches can be measured at one time, the efficiency is doubled, the method is more economical, the dilution of a water sample to be detected is not needed, the nitrogen stripping equipment is not needed, the operation cost is reduced, the method is more stable, the special equipment is added with the reagent, and the result is reliable and controllable.

Inventors

  • JIANG XIAOLEI
  • LI YUNFEI
  • WANG LAN
  • LI WEI
  • HU JING
  • WANG SHASHA

Assignees

  • 山东泰亚环保科技有限公司

Dates

Publication Date
20260512
Application Date
20260410

Claims (5)

  1. 1. The method for accurately and rapidly determining the COD in the high-chlorine wastewater is characterized by comprising the following steps of: Preparing solutions, namely respectively preparing 0.2500mol/L and 0.0250mol/L of potassium dichromate standard solutions, respectively preparing 0.050 mol/L and 0.005 mol/L of ammonium ferrous sulfate standard solutions, respectively preparing 30% mercuric sulfate solution, silver sulfate-sulfuric acid solution and a ferron indicator; Sampling, namely adding 10ml of water sample to be detected into a special COD digestion tube; Adding a masking agent, namely adding the 30% mercury sulfate solution prepared in the first step into the special COD digestion tube with a corresponding volume by using a graduated straw, and calculating the adding amount according to the mass ratio of the mercury sulfate to chloride ions of 18-30:1; step four, oscillation complexing, namely fixing the special digestion tube for COD in the step three in an oscillator, and oscillating for 30 minutes at the frequency of 60 times/min to fully complex and mask chloride ions; Oxidizing, namely adding an oxidizing agent, adding the potassium dichromate standard solution prepared in the step one of 5.00 mL into the special digestion tube for COD by using a pipette with a large belly of 5.00 mL, and shaking uniformly; step six, catalysis, namely adding the silver sulfate-sulfuric acid solution prepared in the step one of 15.0 mL into the special digestion tube for COD, and shaking uniformly; Step seven, reflux digestion, namely installing a condensing tube, and placing the special digestion tube for COD in a COD constant-temperature heating reflux device for heating and refluxing, so that uniform heating, complete digestion and no volatilization loss are ensured; Step eight, titration measurement, namely adding water into the special COD digestion tube to dilute to about 140mL after cooling, titrating the standard solution of ferrous sulfate prepared in the step one with the ferrous sulfate prepared in the corresponding concentration to a terminal point by using the ferrous sulfate indicator prepared in the step one, recording the volume, and simultaneously performing blank test and measuring each group in parallel for 6 times; step nine, calculating the result according to the formula ρ= Calculating the mass concentration rho (mg/L) of the chemical oxygen demand in the water sample to be detected; wherein: V0-blank volume of ferrous ammonium sulfate standard solution (mL); V1, the volume (mL) of a ferrous ammonium sulfate standard solution consumed by a water sample to be detected; Concentration (mol/L) of the standard solution of C-ferrous ammonium sulfate; v2-volume of water sample to be measured (mL); 8000. -a scaling factor.
  2. 2. The method for accurately and rapidly determining COD in high-chlorine wastewater according to claim 1, wherein in the fifth step, the adaptive potassium dichromate standard solution is added according to the estimated mass concentration of COD in the water sample to be determined, when the mass concentration of COD in the water sample to be determined is greater than 50mg/L, the potassium dichromate standard solution is selected to be 0.2500mol/L, and when the mass concentration of COD in the water sample to be determined is less than 50mg/L, the potassium dichromate standard solution is selected to be 0.0250 mol/L.
  3. 3. The method for accurately and rapidly determining COD in high chlorine wastewater according to claim 2, wherein in the eighth step, when the mass concentration of COD in the water sample to be determined is greater than 50mg/L, the method is characterized in that the method is used for titration by using 0.050 mol/L of ferrous ammonium sulfate standard solution, and when the mass concentration of COD in the water sample to be determined is less than 50mg/L, the method is used for titration by using 0.005 mol/L of ferrous ammonium sulfate standard solution.
  4. 4. The method for accurately and rapidly determining COD in high-chlorine wastewater according to claim 1, wherein the concentration of chloride ions in the water sample to be detected is 1000-40100 mg/L.
  5. 5. The method for accurately and rapidly determining COD in high-chlorine wastewater according to claim 1, wherein the COD detection interval of the water sample to be detected is 15.9-260 mg/L.

Description

Method for accurately and rapidly determining COD in high-chlorine wastewater Technical Field The invention relates to the technical field of sewage detection, in particular to a method for accurately and rapidly determining COD in high-chlorine wastewater. Background In the prior art, two standards are generally used for determining Chemical Oxygen Demand (COD) in surface water, domestic sewage and industrial wastewater. When the concentration of the chlorine-containing compound is less than 1000mg/L, the method is measured by adopting the national environmental protection standard HJ 828-2017 of the people's republic of China, and the method is not suitable for the brine with the chloride ion concentration of more than 1000 mg/L. When the chloride ion concentration is more than 1000mg/L, the method is measured by adopting the national ecological environment standard HJ/T70-2001 of the people's republic of China, the interference of the chloride ions is eliminated by adopting a nitrogen stripping auxiliary chlorine correction method, a water sample with the chloride ion concentration of more than 1000mg/L can be masked, and the detection lower limit of the method is 30 mg/L. However, the method is only suitable for the measurement of the chloride ion concentration of 1000 mg/L-20000 mg/L, when the chloride ion concentration is more than 20000mg/L, no suitable method is available at present, the water sample can be only diluted and then measured, but after the water sample is diluted, the problem that COD is lower than the detection limit can be caused, and the measurement result is inaccurate. The HJ 70-2025 standard implemented in 7/1 of 2026 is also adopted to adopt a nitrogen stripping and chlorine absorption correction mode, nitrogen is continuously introduced in the water sample reflux digestion process, and chlorine generated by the reaction is stripped into sodium hydroxide absorption liquid to complete quantitative absorption. The standard of the two chlorine correction methods suitable for the high-chlorine wastewater adopts a nitrogen stripping and chlorine absorption correction mode to eliminate chloride ion interference, nitrogen is continuously introduced in the water sample reflux digestion process, and the chlorine generated by the reaction is stripped into sodium hydroxide absorption liquid to complete quantitative absorption, and the whole set of detection is completed in a reflux triangular bottle. According to the method, not only is the COD value of the water sample determined by titration needed, but also an independent titration calculation correction value is additionally carried out on the nitrogen stripping absorption liquid, a group of titration detection steps are added, the control requirement of the nitrogen stripping process is strict, nitrogen is consumed, the operation steps are complex and complicated, the detection time is long, the manpower consumption is high, the overall monitoring cost is high, the detection efficiency is low, the accuracy and the precision of the detection result are difficult to be stably ensured, and meanwhile, the synchronous and efficient monitoring of a large number of high-chlorine water samples cannot be realized. The application range of chloride ions of the two standards cannot cover the interval of 20000mg/L to 40000mg/L, aiming at a water sample with lower COD content in the interval, the data obtained by adopting high concentration monitoring and low concentration monitoring of partial water samples are quite different, the difference is quite large, if the water sample is diluted, the COD value is easily diluted to be less than 50mg/L, the measurement is carried out by switching a low concentration method, and the data obtained by the two concentration methods are quite different. When the COD of the water sample is low, no matter a high-concentration or low-concentration detection system is adopted, the dilution operation is not suitable, the COD after dilution is very easy to be lower than the detection lower limit of the method, and effective and reliable data cannot be obtained. Therefore, in the water sample monitoring with higher chloride ion concentration and lower COD value, the method is not suitable for detection in a dilution mode, and the existing standard method is difficult to meet the accurate measurement requirement of the water sample with high chloride and low COD. For the sewage treatment plant in coastal areas, the concentration of the received industrial wastewater and the chloride ions of water samples of all treatment units (such as an adjusting tank, a coagulation tank, a biochemical tank, a hydrolysis tank and the like) in the plant generally exceeds 1000mg/L, and if all the wastewater treatment plants depend on a chlorine correction method for COD monitoring, great workload and cost pressure are brought to enterprises. Therefore, developing a method for rapidly and accurately measuring COD of high-chlorine wastew