Biological oxygen demand (BOD) is the amount of oxygen consumed by microorganisms growing in a certain amount of water. It is an environmental monitoring indicator, mainly used to monitor the pollution of organic substances in water.
For general domestic sewage and industrial wastewater, although there are many organic substances, if the sample contains enough microorganisms and oxygen, the sample can be directly determined. However, in order to ensure the growth of microorganisms, a certain amount of inorganic nutrients (phosphate, calcium, magnesium and iron salts) should be added. Some industrial wastewater without or less microorganisms, wastewater with high pH, wastewater treated with high temperature or chlorination sterilization, etc. shall be connected with microorganisms capable of decomposing organic matters in the water before determination. This method is called inoculation. If there are organic substances or toxic substances in some wastewater that are difficult to be degraded by microorganisms in ordinary domestic sewage at normal speed, the water sample can be properly diluted and inoculated with acclimated inoculation water containing adaptive microorganisms.
Key points for use of BOD detector:
1. The BOD value of the tested sample can be estimated in advance. If it cannot be estimated, it can be calculated with the help of chemical oxygen demand (CODCr). Generally, BOD is calculated as 70% of chemical oxygen demand (CODCr). Select the number of parallel samples to be prepared according to the number of water samples and 8 culture bottles. The water sample must be pretreated and its PH value should be about 7.2.
2. If the CO2 absorbent enters the sample, the sample shall be poured out and a new sample shall be prepared. Note that each bottle is matched with the sealing cap and pipe, and the cap cannot be interchanged and screwed incorrectly, otherwise the data will not correspond to the water sample in the bottle.
3. If the rotor in the culture bottle does not rotate well, gently shake the bottle to rotate it, but do not shake it too much to cause the CO2 absorbent to enter the water sample.
4. During normal measurement, the constant temperature waiting time cannot be less than 1 hour or more than 3 hours, otherwise the measurement results will be affected. Select constant temperature for 1 hour when the ambient temperature is close to 20 ℃, and appropriately extend the constant temperature waiting time within the range when the temperature difference with 20 ℃ is large.
5. Data processing: the instrument can directly read the concentration according to the set sampling amount. The user only needs to average the parallel samples of the same sample, which is the BOD value of this water sample.
6. When cleaning culture bottles, sealed cups and rotors, mechanical methods can be used to remove dirt, and ultrasonic cleaners can be used if conditions permit.