COD/BOD/SS Index in water Treatment
COD
COD is a commonly used comprehensive index to evaluate the degree of water pollution. It is the abbreviation of chemical oxygen demand. It refers to the amount of oxygen consumed by the oxidation and decomposition of reducing substances in water by chemical oxidants. It reflects the extent to which water is polluted by reducing substances. Because organic matter is the most common reducing substance in water, COD reflects the degree of organic pollution to a certain extent. The higher the COD, the more serious the pollution.
Harm of COD
The higher COD, the higher the content of reducing substances (such as organic matter) in water, and reducing substances can reduce the content of dissolved oxygen in water, leading to anoxia and even death of aquatic organisms, water quality corruption and odor. In addition, benzene, phenol and other organic substances have strong toxicity, which will cause direct damage to aquatic organisms and human body. Therefore, COD is the key control index of water pollution.
Sources of COD
Organic substances in water mainly come from the discharge of domestic sewage and industrial wastewater, as well as the decomposition of animals and plants, which flow into the water body with rainfall.
COD Control Measures
Firstly, control the source, prohibit discharging waste chemical reagents, waste oil, organic waste liquor, high concentration organic waste water and other pollutants into urban drainage system. Secondly, we should improve the centralized treatment rate of urban domestic sewage, collect all domestic sewage into sewage pipelines, and transfer it to urban sewage treatment plants for discharge or reuse after treatment, thus eliminating the phenomenon that sewage is directly discharged into rainwater pipelines and environmental water bodies such as rivers, lakes and reservoirs. Finally, to control industrial emissions, especially in chemical, pharmaceutical, textile and food processing industries, on the basis of stable discharge of wastewater, further deepening treatment and reuse, reducing COD emissions.
BOD
BOD is the abbreviation of biochemical oxygen demand and represents the comprehensive index of the content of aerobic pollutants such as organic substances in water. It means the total amount of dissolved oxygen consumed by organic matter in water when it is inorganized or gasified due to the biochemical action of microorganisms. The higher the value, the more organic pollutants in water, the more serious the pollution.
The calculation of BOD is as follows:
BOD (mg/L) = (D1-D2)/P
D1: Initial dissolved oxygen (mg/l) in diluted water samples
D2: Dissolved oxygen (mg/l) of diluted water samples incubated in 20 C incubator for 5 days.
P= [Water prototype (ml)]/ [The final body of diluted water sample (ml)]
The ratio of biochemical oxygen demand to chemical oxygen demand can explain how many organic pollutants in water are difficult to decompose by microorganisms. Organic pollutants, which are difficult to decompose by microorganisms, do more harm to the environment.
SS
SS is the abbreviation of suspended solid. Suspended solids are an important water quality index of wastewater. When discharged into the water body, the appearance of water will be greatly affected. In addition to increasing the turbidity of the water body, hindering the photosynthesis of plants in the water, it will also cause blockage, siltation and disadvantage to the growth of aquatic organisms. Wear and tear. In addition, suspended solids have the ability to adsorb and condense heavy metals and toxic substances.
