What Is a COD Meter?
A COD meter is a device used to measure chemical oxygen demand (COD) in water.
*COD: An indicator used to measure organic pollution in a water sample. The higher the COD value (indicating a higher oxygen demand of the sample), the more polluted the water is.
Similar to COD, biochemical oxygen demand (BOD) is also used as an indicator of water quality.
*BOD: An indicator of the amount of oxygen required by microorganisms to decompose organic matter in water and is used as a reference item for rivers.
Uses of COD Meters
COD measures the amount of oxygen consumed when organic matter is decomposed by an oxidizing agent (often using potassium permanganate). The more organic matter there is, the more oxygen is required when the oxidizer is added, and thus the higher the COD.
Standard and target values for COD are generally set by government environmental agencies and serve as criteria for environmental assessment and wastewater treatment. These standard values vary depending on the type of water body and the intended use of the water, such as for seaweed cultivation and industrial water. COD is expressed in mg/L, but it is important to note that the value varies depending on the measurement method.
Principle of COD Meters
The following methods are used as measurement methods for COD meters.
1. Automatic COD Analyzers (Acidic and Alkaline Methods)
The acidic method accounts for the largest share of automatic COD analyzers.
This method automates the entire process from adding reagents to the sample to heating and potassium permanganate measurement.
The following methods are employed in simple COD meters. It can be easily measured in the field or on-site.
2. Coulometry (Electrolytic Measurement) Method
An electrode is placed in the sample and electrolyzed to produce an oxidant for titration. The COD concentration is determined based on the amount of electricity used in the titration.
3. Colorimetric Method
The residual amount of potassium permanganate, an oxidant, is determined by irradiating the sample with a certain wavelength and determining the absorbance. Based on this, COD is calculated. Note that the absorbance measurement may be affected by the turbidity of the reagent or suspended matter in the sample. A simpler method, the colorimetric method using a pack test, also exists.
Other methods of measurement by manual analysis are also available but will be omitted from this article to focus on COD meters.