The COD (Chemical Oxygen Demand) level in domestic wastewater is an important indicator of the amount of organic pollutants present in the water. It measures the amount of oxygen required to chemically oxidize all organic substances in the water. High COD

What is the COD level in domestic wastewater?

The COD (Chemical Oxygen Demand) level is an index used to evaluate whether domestic wastewater is polluted and to what extent. COD can be understood as the amount of oxygen needed to oxidize the inorganic and organic substances present in wastewater.

A higher COD indicates more pollution in domestic wastewater. Statistics in Vietnam in recent years have shown a significant increase in COD levels. It is estimated that each person discharges around 80 liters of wastewater per day due to daily hygiene activities, laundry, etc.

What are the effects of high COD levels?

A high COD level, ranging from 72 to 102 g/person/day, indicates severe pollution in domestic wastewater. This condition, if left unchecked, can lead to significant adverse effects on:

• Environment: Causes pollution not only in the soil environment where wastewater is discharged but also in the adjacent areas and the air environment. The waste components exist in solid, liquid, and gas states. Gaseous waste emits a strong foul odor that is extremely unpleasant.
• Plant and animal health: Species that use domestic wastewater as a source of life will eventually encounter various diseases due to exposure to harmful toxic substances.
• Human health: Causes skin inflammation, allergic reactions, digestive system diseases, respiratory issues, etc.

How to determine the COD level in domestic wastewater

The COD level in domestic wastewater can be accurately determined by various methods. The typical ones include:

Using Potassium Permanganate

Potassium permanganate, with the chemical formula KMnO4, is used to determine the COD level in wastewater. According to QCVN 01-1:2018/BYT, if the permanganate index in wastewater exceeds 2 mg/L, it indicates high COD levels and severe pollution.

The storage tank or land area containing domestic wastewater will exhibit characteristic signs, such as rapid growth of moss and algae, and the presence of numerous harmful microorganisms.

Using Potassium Dichromate

Potassium Dichromate, with the chemical formula K2Cr2O7, is used to determine the COD level in wastewater in a solution form with a concentration of 0.25N. The COD in the test sample is below 50 mg/L. The chemical equation is as follows:

• CnHaObNc + dCr2O72- + (8d+c)H+ -> nCO2 + (a+8d-3c÷2) H2O + cNH4 + 2dCr3+

The amount of Cr3+ formed after the reaction is an indirect measure of the COD level in the water sample.

Using Potassium Dichromate is an effective and accurate method to determine the COD level in wastewater at a low cost. Therefore, this method is widely used in Vietnam.

Other methods include determination using Potassium Iodate, and Cerium Sulfate. Potassium Iodate has the chemical formula KIO3, and Cerium Sulfate has the chemical formula Ce(SO4)2.

Measures to reduce COD levels

Here, Toan A Environmental Technology Joint Stock Company, with extensive experience and solid professional knowledge, will provide you with information on specific measures to reduce COD levels and wastewater treatment in general:

Wastewater Treatment

It is essential to eliminate, remove harmful substances, and the root cause of high COD levels. This helps prevent all adverse effects on the soil, water, air environment, human health, and plant and animal life.

High COD levels can be easily treated, and toxic substances can be quickly removed from wastewater. Various wastewater treatment methods help ensure that domestic wastewater is discharged into the environment clean and harmless. These methods include:

• Biological treatment of wastewater using aerobic methods.
• Using oxidizing agents such as Ozone, Chlorine, Hydrogen Peroxide.
• Using chemical coagulants like Iron salts, Aluminum salts, PAC.
• Applying the Fenton reaction.
• Utilizing Advanced Oxidation Processes (AOP) technology.

Using Aerobic Microbial Methods

Aerobic microbes are used to reduce COD levels because they live and thrive on excess organic matter and minerals in wastewater. They decompose organic matter and minerals to produce harmless inorganic substances for the environment and health.

The aerobic microbial method in wastewater treatment can use naturally occurring or artificially introduced aerobic microbes. Overall, the wastewater treatment process goes through three stages:

• Oxidizing 100% of the organic matter to meet the cellular energy needs of the microbes: CxHyOzN + (x+ + + ) O2 → xCO2 + H2O + NH3.
• Assimilation, synthesis, and construction of microbial cells: CxHyOzN + NH3 + O2 → xCO2 + C5H7NO2.
• Disintegration, intracellular respiration: C5H7NO2 + 5O2 → xCO2 + H2O; NH3 + O2 → O2 + HNO2 → HNO3.

These are the essential details about COD levels in domestic wastewater. If you have any questions or concerns, feel free to contact us for advice and support.