COD Analysis

What is Chemical Oxygen Demand (COD)?

Chemical Oxygen Demand (COD) is defined as the amount of oxygen equivalents consumed in the chemical oxidation of organic matter by strong oxidant (e.g., potassium dichromate). 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. Chemical oxygen demand (COD) is an indirect measurement of the amount of organic matter in a sample. With testing COD, you can measure virtually all organic compounds that can be digested by a digestion reagent.

COD is critical in wastewater for determining the amount of waste (contamination) in the water. Waste that’s high in organic matter requires treatment to reduce the amount of organic waste before discharging into receiving waters. Why does this matter? If wastewater treatment facilities do not reduce organic content of the wastewater before it reaches natural waters, microbes in the receiving water will consume the organic matter. As a result, microbes will consume the oxygen in the receiving water to breakdown the organic waste. This oxygen depletion is called eutrophication and can lead to the death of animal life.

Chemical oxygen demand tests are typically performed on wastewater. The pollution level is calculated by measuring the amount of organic matter in the water. Water with too much organic material can have a negative effect on the environment in which the wastewater is discharged. 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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HIGH CONTAMINATION

discharged to tributaries and streams can impact:

Toxicity of organic compounds: health effects on plants and wildlife
Decreasing dissolved oxygen and eutrophication
Impact on fish populations

COD monitoring can:

Determine concentrations of oxidizable pollutants in wastewater
Analyze the effectiveness of wastewater treatment solutions
Determine the effect of wastewater disposal on the environment
As an index for determining overall water quality

Typical oxidants include:

Potassium dichromate
Potassium iodate
Potassium permanganate
Ceric sulphate

COD analysis takes place in two stages:

Digestion – oxidizing the organic substances in the sample
Determination – measuring COD using either the titrimetric or colorimetric method

DEFINITION OF TOTAL 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.

With this parameter the total oxygen demand of water can be measured. Even in the 1970s online analyzers for the determination of total oxygen demand (TOD) were available. After the rise in popularity of the COD-dichromate method, the TOD had been suppressed in many countries as the COD analysis 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.

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DETERMINING THE CHEMICAL OXYGEN DEMAND WITHIN MINUTES.

COD measurement is accomplished in about 3 minutes. Thus, 3 replication measurements per sample can be determined within less than 10 minutes. The QuickCODlab offers enormous time and cost savings in comparison to standard procedures.

O2 DETECTION. SIMPLE AND RELIABLE.

An O2 detector determines the oxygen used to digest all the constituents. The determination of the oxygen demand is performed over a wide variety of measurement ranges. The QuickCODlab also reliably measures the real COD in relevant measurement ranges from 5 to 100 mg/l.

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ONLINE MEASUREMENT OF COD AND TOC

THERMAL OXIDATION (HIGH TEMPERATURE METHOD)

The 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 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).

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TOC Determination

PURE WATER

Pure water and high purity water are crucial factors of production in numerous processes and industries. Depending on the demand it is used as a raw material, auxiliary or operating material. For water with low particle density, our pure water analyzers are equipped with an injection loop system. Using this closed system like our QuickTOCpurity™ or QuickTOCuv™, influences from ambient air or other influences will be avoided.

UV persulfate oxidation method.

PROCESS WATER

Process water is very diverse regarding to its use. This type of water may contain adhesive and/or toxic substances and are characterized by high and fluctuating loads or a wide variety of compositions. Our cost-effective, QuickTOCultra water analyzer is a continuously working TOC measurement system using the UV persulfate oxidation method.

Harsh Water Analysis

WASTEWATER

Wastewater is one of the most challenging water types for any TOC online analyzers. With highly fluctuating loads, very high salt concentrations and has high particle density, wastewater needs a robust water analyzer. For the toughest applications, our TOC analyzers are equipped with a unique injection system capable of transporting and measuring a high content of solid matter without any filtration.