Chemical Oxygen Demand (COD) - This indicator is one of the comprehensive indicators of organic pollution. It is commonly used internationally as the main pollution control item in the indicators for measuring the environmental quality of water bodies in a region, referred to as COD. It refers to the oxygen content required by organisms in a certain volume of water. Generally, the lower the chemical oxygen demand, the better, because the oxygen in the water is certain, and the low chemical oxygen demand means that the dissolved oxygen in the water can maintain the needs of aquatic organisms; If the chemical oxygen demand is too large, the dissolved oxygen in the water will decrease, resulting in the death of organisms (usually fish and shrimp) that need more oxygen in the water, and the proliferation of anaerobic bacteria, and the "living water" will become "dead water". Generally, the larger the COD value, the more serious the organic pollution of the water body.

Ammonia nitrogen (NH3-N) - refers to the nitrogen that exists in water in the form of free ammonia (NH3) and ammonium ions (NH4). Ammonia nitrogen mainly comes from human and animal excrement. At the same time, rainwater runoff and the loss of agricultural fertilizers are also important sources of nitrogen. Ammonia nitrogen also comes from industrial wastewater such as chemical industry, metallurgy, petrochemical industry, paint and pigment, gas, coking, tanning, and fertilizer. middle. Ammonia nitrogen is a nutrient in water, which can lead to water eutrophication. It is the main oxygen-consuming pollutant in water and is toxic to fish and some aquatic organisms.