Conceptual analysis of wastewater treatment: COD, BOD, ammonia nitrogen, total nitrogen

The evaluation and control of wastewater treatment effectiveness cannot be achieved without precise monitoring of core water quality indicators. Chemical oxygen demand (COD), biochemical oxygen demand (BOD), ammonia nitrogen, and total nitrogen are key parameters that reflect the degree of water pollution and nutritional status, providing scientific basis for wastewater treatment process design and operation regulation. The core concepts and related impacts of these four indicators will be analyzed in detail below.

1. COD (Chemical Oxygen Demand)

COD: Chemical Oxygen Demand (COD or CODcr) refers to the amount of oxidizing agent consumed when reducing substances in water are oxidized and decomposed under certain strict conditions, expressed in mg/L.

Chemical oxygen demand reflects the degree of pollution in water by reducing substances, including organic matter, nitrite, ferrous salts, sulfides, etc. However, the amount of inorganic reducing substances in water and wastewater is relatively small, and pollution by organic matter is common. Therefore, COD can be used as a comprehensive indicator of the relative content of organic matter.

2. BOD (Biochemical Oxygen Demand)

BOD: Biochemical Oxygen Demand, which is an important indicator indirectly indicating the degree of organic pollution in water bodies through the consumption of dissolved oxygen by microbial metabolism.

Its definition is: the amount of free oxygen consumed by aerobic microorganisms to oxidize and decompose organic matter per unit volume of water under aerobic conditions, expressed in mg/L.

3. Ammonia nitrogen

Ammonia nitrogen: refers to the nitrogen present in water in the form of free ammonia (NH3) and ammonium ions (NH4).

Ammonia nitrogen is a nutrient in water bodies that can lead to eutrophication. It is the main oxygen consuming pollutant in water bodies and is toxic to fish and certain aquatic organisms.

4. Total nitrogen

Total nitrogen: The total amount of inorganic and organic nitrogen in various forms in water.

Including inorganic nitrogen such as NO3-, NO2-, and NH4+, as well as organic nitrogen such as proteins, amino acids, and organic amines, calculated in milligrams of nitrogen per liter of water. It is often used to indicate the degree of nutrient pollution in water bodies.