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Overtreatment of COD in Wastewater

What is COD in wastewater?

COD (Chemical Oxygen Demand), also known as chemical oxygen demand, is an important parameter for evaluating wastewater quality. COD measures the amount of oxygen required to oxidize organic matter in wastewater with inorganic oxidants.
The higher the COD content of wastewater, the greater the amount of organic matter in the water, the decomposition process needs more oxygen. Therefore, COD is an important indicator to assess the pollution of water.
The Impact of COD on the Environment
  • Wastewater with high COD content will reduce the amount of dissolved oxygen in the water. This adversely affects aquatic organisms, even causing hypoxia, killing fish.
  • High COD increases the activity of anaerobic bacteria, producing toxic decomposition products such as H2S, CH4 that pollute the environment.
  • High COD wastewater when discharged into rivers and lakes wastes oxygen in the receiving water, reducing the quality of surface water.

Vượt chỉ số COD trong nước thải công nghiệp

COD analysis method in wastewater

  • The method of using dichromate: based on the principle of oxidation of organic matter by potassium dichromate solution at high temperature (150 ℃), in concentrated sulfuric acid medium containing silver ion as catalyst and mercury salt.
  • The method of COD analysis by the device: using a COD analysis device that automatically measures the light absorption of the solution after the reaction.
  • COD chemical method: using pre-packaged COD measuring chemicals with standardized ingredients.
What causes increased cod in wastewater?
  • Domestic wastewater contains a lot of organic matter, grease, food waste is thrown away causing an increase in COD.
  • Wastewater from factories and enterprises contains toxic organic substances such as phenol, ammonium, increasing COD.
  • The anaerobic decomposition of organic matter in sewage sludge, landfill also produces high COD leachate.
  • Excessive occurrence of algae, plankton due to excess nutrient status also increases COD in water sources.

COD treatment technology in wastewater

  • Biological treatment (activated sludge, biofiltration methods, pond sedimentation…) helps bacteria break down organic matter efficiently.
  • Chemical treatment with chlorine, ozone, advanced oxidation helps break down organic molecules.
  • Membrane treatment, activated carbon adsorption removes organic matter.
  • Combining multiple technologies to improve COD processing efficiency.

Vượt chỉ số COD trong nước thải công nghiệp

COD regulation in wastewater according to QCVN

According to QCVN 40: 2011 / BTNMT, the allowable limit of COD in industrial wastewater is stipulated:
  • Wastewater flows directly to the receiving source: 100-200 mg/L
  • Wastewater flows into municipal sewer systems: 300-500 mg/L
  • Wastewater discharged into the general sewer of production, business and service areas: 300-600 mg/L
Thus, the monitoring and treatment of COD in wastewater is essential to protect the water environment. Modern treatment technologies need to be applied to ensure that the COD concentration is up to standard before being discharged to the water source.

Excessive COD treatment unit in wastewater

Natural Star Vina is a Korean company specializing in consulting, designing and constructing reputable wastewater treatment systems with many years of experience in deploying hundreds of different large and small projects. All systems that Natural Star designs and operates have reached the COD index in wastewater according to the Ministry of Natural Resources and Environment regulations QCVN 40: 2022 / BTNMT before discharging waste into licensed water sources.

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