Methods and comparisons for the determination of total oxygen demand and biochemical oxygen demand
Total chemical oxygen demand (COD) and biochemical oxygen demand (BOD) are two important indicators to measure the degree of organic matter pollution in water bodies.
OnecodAssay method
Potassium dichromate methodThis is a commonly used method for the determination of COD, the principle of which is to use potassium dichromate solution to oxidize with the organic matter in the water sample, and the amount of oxidant consumed is proportional to the organic matter content in the water sampleThis method is simple to operate, but it is susceptible to interference from inorganic substances such as chloride ions.
Potassium permanganate method: This method calculates COD by measuring the oxidation dose consumed by using an oxidation reaction of a potassium permanganate solution with organic matter in a water sampleThe potassium permanganate method has less interference with chloride ions, but the pH value needs to be strictly controlled during operation.
Silver sulfate method: This method is based on the oxidation of silver sulfate with organic matter in a water sample, and the COD is calculated by measuring the amount of silver sulfate consumedThe advantage of the silver sulfate method is that it has strong anti-interference ability, but the operation is complex, and the treatment of silver sulfate waste liquid is difficult.
IIbodAssay method
Five-day biochemical oxygen demand (BOD)5-day bodIn this method, the water sample is placed at a constant temperature, a certain amount of microorganisms are added, and the amount of dissolved oxygen consumed by the oxidation of organic matter by microorganisms is determined within 5 daysThe 5-day BOD could better reflect the biodegradability of organic matter in the water body, but the measurement period was longer.
Seven-day biochemical oxygen demand (7-day bod: Similar to the 5-day BOD, except that the assay period is extended to 7 days;The 7-day BOD measurement results are more accurate, but take a long time.
Photosynthetic bacteria method: This method uses photosynthetic bacteria to oxidize and decompose organic matter in water samples, and calculates BOD by measuring the growth of photosynthetic bacteriaThe advantage of the photosynthetic bacteria method is that the measurement speed is fast, but the operation is complex and the requirements for water quality are high.
3. Comparison
1.Determination principle: COD reflects the organic matter content by measuring the oxidation dose consumed by the oxidation of organic matter in the water sample, while BOD reflects the biodegradability of organic matter by measuring the amount of dissolved oxygen consumed by microbial oxidative decomposition of organic matter in the water sample.
2.Measurement range: COD has a wide range of determination, including organic and inorganic substances in water;BOD mainly focuses on organic matter in water and focuses on the evaluation of biodegradability.
3.Determination speed: The determination speed of COD is relatively fast, generally completed in tens of minutes to several hours;BOD is measured over a long period of time, usually 5 or 7 days.
4.Anti-interference ability: COD has strong anti-interference ability, but it is susceptible to interference by inorganic substances such as chloride ionsBOD has high requirements for water quality and relatively weak anti-interference ability.
5.Application field: COD is widely used in environmental monitoring, sewage treatment and other fields to evaluate the degree of organic pollution in water bodiesBOD is mainly used to evaluate the biodegradability of water and evaluate the self-purification ability of water body.