ZL2000 COD Sensor

1. UV-Vis Absorption Spectroscopy (Most Common)

This method is based on the principle that organic molecules absorb ultraviolet (UV) light.

• Principle: The sensor emits ultraviolet light (typically at 254 nm wavelength) through a water sample. Organic compounds (especially those with conjugated double bonds and aromatic rings like humic acids, phenols, and dyes) absorb this UV light.

• Measurement: A detector on the other side measures the intensity of the light that passes through (transmits). The amount of light absorbed (absorbance) is calculated using the Beer-Lambert law.

• Correlation to COD: There is a strong correlation between the UV absorbance (UV254) and the COD value for a given, consistent wastewater stream. The sensor is calibrated against laboratory COD results for that specific type of water to create a conversion algorithm.

• Advantages: No reagents, very fast response (seconds to minutes), continuous measurement, low maintenance.

2. Electrochemical Method (PeCOD® – Photoelectrochemical Oxygen Demand)

This is a more advanced and accurate method that closer mimics the oxidation principle of the standard COD test.

• Principle: A highly reactive hydroxyl radical (•OH) is generated photoelectrochemically on the surface of a special electrode (often a nano-titanium dioxide electrode) by shining UV light on it.

• Oxidation: These radicals aggressively oxidize the organic compounds in the water sample.

• Measurement: The electrical current generated by this oxidation reaction is measured. This current is directly proportional to the amount of organics oxidized, and thus to the COD.

• Advantages: More accurate than UV absorption, especially for waters with varying compositions, and faster than the lab test (results in minutes).