C.O.D Digestor

Product Description

A C.O.D. Digestor, also known as a COD digestion apparatus or thermoreactor, is a crucial piece of laboratory equipment used for determining the Chemical Oxygen Demand (COD) of water and wastewater samples.

What is COD?

COD is a measure of the amount of oxygen required to chemically oxidize the organic and inorganic pollutants present in a water sample. It's a vital indicator of water quality, providing a rapid estimate of the pollution level, especially from industrial and municipal sources.

How Does a C.O.D. Digestor Work?

The fundamental principle of a COD digestor is to create a controlled environment of high temperature and acidity to fully oxidize the contaminants in a water sample. Here's a simplified breakdown of the process:

1. Sample Preparation: A water sample is collected and placed into specialized digestion vials.

2. Reagent Addition: A strong chemical oxidizing agent, most commonly potassium dichromate (K2Cr2O7), and a strong acid, like sulfuric acid (H2SO4), are added to the sample. A catalyst, such as silver sulfate, is also often included to speed up the reaction.

3. Digestion: The vials are placed into the COD digestor, which is essentially a heating block with multiple holes for the vials. The digestor heats the samples to a specific temperature, typically around 150C, and holds them there for a set period, usually two hours. This controlled heating process ensures a complete and consistent oxidation of the organic matter.

4. Analysis: After the digestion period, the samples are cooled. The amount of unreacted potassium dichromate is then measured. This can be done in two primary ways:

   • Titration: A reducing agent, such as ferrous ammonium sulfate (FAS), is used to titrate the remaining dichromate. The amount of FAS consumed is directly related to the amount of dichromate that was used to oxidize the sample.

   • Colorimetry/Spectrophotometry: The amount of chromium that was reduced from its hexavalent form (orange) to its trivalent form (green) is measured using a colorimeter or spectrophotometer. The intensity of the green color is directly proportional to the amount of oxygen consumed during the digestion.