Seawater COD Measurement via Electrodialysis Chloride Removal
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Solution Overview
Problem
Existing methods for determining chemical oxygen demand (COD) in seawater are hindered by chloride ion interference, leading to inaccurate measurements and the need for toxic masking agents.
Innovation Solution
The method employs electrodialysis (ED) to remove chloride ions from seawater, followed by oxidation with an oxidizing agent and colorimetric titration to calculate COD, without using chloride masking agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional COD measurement methods (potassium dichromate oxidation) are used in seawater, then oxidation power is sufficient to break down organic matter, but chloride ions interfere with the measurement leading to inaccurate results
Solution Approach 1:
The patent removes chloride ions from the seawater sample before COD analysis through ion-exchange chromatography or precipitation methods. This extraction of the interfering substance (chloride) allows the subsequent COD measurement to proceed without interference, resolving the contradiction between sufficient oxidation power and measurement accuracy in the presence of chloride ions.
Solution Approach 2:
The patent applies preliminary treatment to the seawater sample to remove or mask chloride ions before the COD measurement process. By performing this preparatory action of chloride removal in advance, the measurement can then be conducted under ideal conditions without chloride interference, achieving both accurate measurements and eliminating harmful factors.
2Measurement precision
If chloride masking agents (such as mercuric sulfate) are added to eliminate interference, then measurement accuracy improves, but toxic substances are introduced creating safety and environmental concerns
Solution Approach 1:
The patent converts the harmful effect of chloride ions into a beneficial separation process. Instead of using toxic masking agents that simply mask the interference, the method physically separates chloride ions from the organic matter through ion-exchange or precipitation, transforming the problematic chloride presence into a useful purification step that eliminates both interference and toxicity.
Solution Approach 2:
The patent introduces an intermediary substance (such as silver sulfate or ion-exchange resins) that selectively interacts with chloride ions to remove them from the sample. This intermediary acts as a mediator that targets only the interfering chloride ions without introducing the widespread toxicity of mercuric sulfate, thus improving measurement accuracy while minimizing harmful effects.
3Object-affected harmful factors
If sample dilution is used to reduce chloride content, then chloride interference decreases, but the concentration of organic matter also decreases affecting detection sensitivity
Solution Approach 1:
The patent segments the complex seawater matrix into separate components: chloride ions are separated from organic matter through ion-exchange chromatography or selective precipitation. This segmentation allows chloride to be removed or set aside while the organic matter remains concentrated in the analyzed portion, thus reducing interference without sacrificing detection sensitivity.
Solution Approach 2:
The patent applies local quality by creating different chemical environments for different components. The sample is treated in a way that selectively affects chloride ions (through pH adjustment, ion-exchange, or precipitation) while leaving organic matter unchanged. This localized treatment removes chloride interference from specific portions of the sample without diluting the overall organic matter concentration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for accurate determination of COD in seawater at low concentrations, overcoming chloride interference and eliminating the need for toxic masking agents, thereby improving measurement accuracy and safety.
Implementation Method 1
dialyzing the seawater including chloride ions and at least one organic compound with an electrodialysis unit to form a processed seawater having at least 25% less chloride ions than the seawater
Implementation Method 2
The anode compartment and the cathode compartment are connected to a power supply. The power supply provides a direct current voltage of 5-30 volts (V).
Implementation Method 3
mixing the processed seawater with an oxidizing agent to oxidize the at least one organic compound
Implementation Method 4
performing a colorimetric titration on the titration solution with a reducing agent so as to reduce any excess of the oxidizing agent
Data Source
AI summary
A method of measuring chemical oxygen demand (COD) in seawater including dialyzing the seawater including chloride ions and at least one organic compound with an electrodialysis unit to form a processed seawater having at least 25% less chloride ions than the seawater; mixing the processed seawater with an oxidizing agent to oxidize the at least one organic compound and heating to 100-200° C. for 1-5 hours to form a digested solution. The method further includes cooling the digested solution and adding an indicator to form a titration solution, and further performing a colorimetric titration on the titration solution with a reducing agent so as to reduce any excess of the oxidizing agent and reach an equivalence point based on the indicator. The COD in the seawater is calculated based on an amount of reducing agent used in the colorimetric titration.