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BOD Overtreatment in Industrial Wastewater

What is BOD in wastewater

BOD (Biochemical Oxygen Demand) also known as Biochemical Oxygen Demand is an important parameter for assessing water pollution. BOD is the amount of oxygen required for microorganisms to decompose organic matter in water.
Domestic wastewater, industrial wastewater often contain organic matter that is easily biodegradable such as proteins, carbohydrates. When discharged into water sources, these organic matter is decomposed by microorganisms, using oxygen dissolved in water. The amount of oxygen needed for this decomposition process is BOD.
Water that contains a lot of organic matter will have a high BOD. The higher the BOD, the more severe the pollution level, causing hypoxia for aquatic organisms. Therefore, BOD is an important parameter to assess wastewater quality before discharging to the receiving source.

The impact of BOD on the environment

Wastewater with high BOD content when discharged into water sources will cause the following adverse effects:
  • Reduces the amount of dissolved oxygen in water: The process of decomposition of organic matter consumes large amounts of oxygen, leading to a decrease in the concentration of dissolved oxygen. This makes it difficult for aquatic organisms to breathe.
  • Eutrophication: The high concentration of phosphorus and nitrogen in the wastewater stimulates the overgrowth of algae. When algae die, it reduces the amount of dissolved oxygen, causing eutrophication.
  • Reduces biodiversity: Lack of oxygen causes many aquatic species to die. At the same time, phytoplankton species, thriving algae also compete for oxygen with other species. This reduces the biodiversity of the ecosystem.
  • Microbiological pollution: Wastewater with high levels of organic matter is an ideal environment for bacteria to grow. Some pathogenic bacteria can enter water sources, causing pollution and spreading disease.
  • Odors: The decomposition of organic matter produces substances such as ammonia, hydrogen sulfide, etc…It causes an unpleasant smell.
Thus, high BOD in wastewater causes diverse adverse impacts on the water environment. BOD control and treatment is extremely necessary to protect water resources.
Xử Lý BOD Trong Nước Thải Công Nghiệp

Analysis method BOD in wastewater

There are many methods of BOD analysis in wastewater, some common methods such as:
  • Winkler method: Based on the principle of measuring oxygen consumption after 5 days (BOD5) at 20 ℃ under constant stirring condition. Standard method for BOD determination.
  • Electrochemical method: Use electrochemical sensor to measure the dissolved oxygen concentration initially and after a period of incubation. Thereby calculate the amount of oxygen consumed.
  • Infrared spectroscopy method: Measure the infrared light absorption of the water sample after annealing, thereby calculating the BOD concentration.
  • Microorganisms: Use light-emitting microbial strains to measure the decrease in brightness when exposed to wastewater. The more the brightness decreases, the higher the BOD.
  • Biosensors: Use enzymes or microorganisms fixed on the sensor surface to react with BOD in water. The results are measured by electrical signals.

BOD in wastewater overtreatment technology

In order to minimize the impact of BOD on the environment, wastewater should be treated to reduce BOD content before being discharged to the receiving source. Some common BOD treatment technologies in wastewater:
  • Aerobic biological treatment: Use aerobic microorganisms to decompose organic matter under oxygenated conditions. The microorganisms will convert organic matter into CO2, water and inorganic substances.
  • Anaerobic biological treatment: Application of anaerobic microorganisms under hypoxic conditions to decompose organic substances.
  • Aerobic-anaerobic bioremediation: Combining both aerobic and anaerobic bioremediation processes to optimize treatment efficiency.
  • Chemical treatment: Using chemicals such as chlorine, ozone to oxidize organic matter in wastewater.
  • Membrane treatment: Use microbiological filter to retain microorganisms that decompose organic matter. Wastewater passing through the membrane will reduce BOD content.
  • Activated sludge treatment: BOD is removed by the process of adsorption and surface activation of the activated sludge.
Depending on the source of wastewater and treatment requirements, appropriate technology can be selected to treat BOD effectively.

BOD in wastewater on QCVN regulation

Wastewater before being discharged into the environment must be treated according to environmental technical regulations. In Vietnam, BOD in wastewater is stipulated in QCVN 14: 2008 / BTNMT – National technical regulations on domestic wastewater.
Accordingly, the maximum BOD level allowed in domestic wastewater when discharged into water sources is:
  • Discharge into water sources for domestic water supply purposes: 30 mg/L (daily average), 50 mg/L (hourly maximum)
  • Waste to municipal drainage: 50 mg/L
  • Discharge into water not used for domestic water supply: 100 mg/L
Thus, depending on the source of reception, domestic wastewater must be treated to the specified BOD level before discharge. This is a mandatory standard to protect water resources.

Overtreatment BOD in wastewater

In order to treat wastewater that exceeds BOD, the units will apply appropriate biological and chemical treatment technologies to remove organic matter and reduce BOD below the permitted threshold before being discharged into the environment.
Thus, Natural Star Vina has synthesized the basic contents related to BOD in wastewater, from concept, influence, analytical methods, treatment technology and regulations.

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