COD Water Analysis

Measure Chemical Oxygen Demand Reliably

What is COD Water Analysis?

Monitor COD Impurities in all Types of Water

Chemical Oxygen Demand (COD) is the amount of oxygen needed to chemically break down organic matter in water using strong oxidants like potassium dichromate. Essentially, the COD value indicates the oxygen required to oxidize all organic substances in the water, measured in mg/l or g/m3. As such, COD water analysis serves as a crucial tool for measuring the organic content in a sample, as it can quantify nearly all organic compounds that can be digested by a digestion reagent.

Moreover, COD water analysis is essential in wastewater management for determining contamination levels. If wastewater contains high organic content, it must be treated before being discharged into receiving waters. Why is this so important? Without proper treatment, microbes in natural water bodies will consume the organic matter, depleting the oxygen in the water. This process, known as eutrophication, can ultimately lead to the death of aquatic life.

In addition to COD water analysis, it is equally important to monitor other key parameters like total organic carbon (TOC), biological oxygen demand (BOD), and total nitrogen (TN). By doing so, facilities can maintain water quality and ensure compliance with environmental regulations. Hence, comprehensive monitoring is crucial for protecting ecosystems and meeting environmental standards across diverse industries.

COD – Chemical Oxygen Demand

The COD value indicates the amount of oxygen which is needed for the oxidation of all organic substances in water in mg/l or g/m3.

The COD (Chemical Oxygen Demand) is closely related to the laboratory standard method named Dichromate-Method. With this method the chemical oxygen demand is determined during chromic acid digestion of organic loads in wastewater. Based on this method the COD became a commonly used sum parameter in wastewater analysis. It is used for planning of wastewater treatment plants, for controlling the cleaning efficiency and for the calculation of wastewater taxes.

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OTHER WATER APPLICATIONS

BOD
COD
TN_b
TOC

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Common Water Detection Methods

Dichromate Method (Wet Chemical Oxidation)

As the dichromate method needs about 2 hours for oxidation and it uses hazardous chemicals such as chromic acid, mercury suphate, sulphuric acid and titration reagents, it is not suitable for online analysis. Also due to the heavy usage of toxic chemicals this method is not acceptable for laboratory personal. High requirements of occupational safety need to be observed, as well as the disposal regulations in respect of the environment. High operational and subsequent costs are the result and consequently industries and operators are looking for online sum parameters and ‘clean’ methods, without a second pollution due to the chemicals involved.

Clean methods to determine the oxygen demand

In the United States the TOD (Total Oxygen Demand) has been standardized and is used as a reference to the oxygen demand of organic substances in wastewater. Another clean method to determine the chemical oxygen demand is the electrochemical oxidation using OH-radicals.

Definition of TOD – Total Oxygen Demand

With this parameter the total oxygen demand of water can be measured. Even in the 1970s online analyzers for the determination of TOD were available. After the rise in popularity of the COD-dichromate method the TOD had been suppressed in many countries as the COD prevailed in analysis of wastewater. However, the total oxygen demand is a reliable and reproducible parameter to indicate the oxygen demand of water. In the United States it is standardized with the ASTM D6238 and very commonly used. The TOD correlates easily to the COD. Hence, this parameter is a preferable alternative to the COD measurement. Moreover, it is very suitable for online measurements, especially with the thermal combustion method at 1,200°C.

Online Measurement of COD and TOD

Thermal Oxidation (High Temperature Method)

The LAR™ QuickCODlab™ -analyzers use a special thermal combustion method at 1,200°C, which allows a catalyst-free oxidization of the complete sample including any particles. Following which an oxygen detector determines the amount of oxygen consumed by the combustion. This very fast analysis has a cycle time of only 3 minutes and does not require any chemicals. The QuickCODultra™ analyzer measures the oxygen demand of all oxidizable substances in the wastewater including organic nitrogen.

Correlation between TOC and COD

The COD concentration is calculated by use of this method that is correlated by a factor and the TOC concentration in the wastewater is determined by use of a standard TOC analysis method. The COD/TOC correlation factor is defined by comparing the measured online COD results to those of the laboratory method. This method is well suited to applications where the concentrations of pollution are not subject to strong fluctuations.

Electrochemical measurement principle

With the patented Lead-Dioxide-Electrode by LAR OH-radicals are produced. Compared to other oxidants OH-radicals have a significantly higher oxidation potential. Thus, hard to oxidize substances can be fast and easily oxidized without using dangerous chemicals. During the reaction the electricity produced will be measured, which is proportional to the consumed OH-radicals. The OH-radicals are here again directly related to the COD. This method offers a fast, simple, accurate and pollution-free alternative to the common dichromate method (wet chemical method).