Biochemical Oxygen Demand Measurement Laboratory
Biochemical Oxygen Demand Measurement Laboratory
Biochemical oxygen demand (Biochemical oxygen demand, referred to as BOD) refers to the conditions in the presence of oxygen, microbial decomposition of organic matter in the water in the biochemical process of the mass concentration of dissolved oxygen required to oxygen mg / L said. More organic matter in the water, the consumption of dissolved oxygen is more, biochemical oxygen demand is also high. Biochemical oxidation of organic substances, generally divided into two stages, the first stage for the hydrocarbon oxidation of carbon dioxide and water, known as the carbonation stage, at 20 ℃ below 20 days, but at 20 ℃ 5 days up to 68%; the second stage of ammonia is oxidized to nitrite and nitrate, known as the nitrification stage, in order to reach a completely stable state, at 20 ℃ in the need for 100 days or so, due to the longer time. In addition to long-term research work, there is no practical application value.
Operation method
dilution culture method
Principle
First, the choice of measurement methods 1. direct culture method: this method is applicable to BOD5 value does not exceed 7mg / l of water samples. 2. dilution culture method: when the oxygen consumption exceeds the dissolved oxygen in the water samples, need to use the preparation of saturated dilution of water to dilute the water samples, and then determine the oxygen consumption. General water samples BOD5 value of 10mg / l or more using this method. 3. Instantaneous oxygen demand: for water samples containing sulfide, sulfite, ferrous and other reducing inorganic substances, sometimes need to determine the instantaneous oxygen demand. In general, this step can be omitted.
Materials and Instruments
watery Move Follow the instrument instructions. Caveat 1. When using dilution culture method, the blank value of dilution water is required, and the experimental conditions must be strictly controlled. 2. Dilution of water source of different blank values. Ion exchange water is susceptible to contamination by the resin bed, should not be used, and generally distilled water as a dilution source, 20 ℃ BOD5 value of up to 0.2 mg / L, the blank value can reach the specified requirements. 3. the collection of water samples should be filled with containers, to prevent aeration, and sealed. 0 ~ 4 ℃ preservation, generally analyzed within 4 h. 4. the nitrification of BOD5, the nitrification of water, and the nitrification of water. 4. Nitrification has an effect on BOD5 value, bacteria use nitrification to increase oxygen consumption, resulting in higher BOD value, you can add a certain amount of nitrification inhibitors, such as allyl thiourea, etc., to inhibit nitrification of nitrogen-containing compounds by bacteria. 5. When the microorganisms in the water sample is very small, should be inoculated, the standard inoculum material used is stored at 20 ℃ under the condition of 24 ~ 36 hours of clarified domestic sewage. 6. Water samples should be measured immediately after collection. In the storage period between sampling and analyzing the sample, the sample has significant degradation, which can affect the BOD value. If left at 15-20°C for a few hours, the BOD content can be reduced by one-half; if stored under freezing conditions for 3 days, the BOD value will be reduced by 5%. 7. Heavy metal salts have an inhibitory effect on the growth of microorganisms, thus affecting the BOD value. These ions can be eliminated by neutralization, precipitation, ion exchange, etc. 8. Determine the dilution times of water. When the water has a high content of organic matter, the first need to determine the value of oxygen consumption or chemical oxygen demand and then deduce the BOD value to determine the dilution times. Usually surface water (OC> 5mg / L) to OC / 1 ~ 3 of the quotient as the water samples required to dilute times; industrial wastewater to CODCr / 4 ~ 5 of the quotient as the water samples required to dilute times. 9. Sample dilution, water samples and diluted water siphon tube into the bottom of the container, gently into the prevention of air bubbles.10, generally believe that the diluted water samples at a temperature of 20 ℃, after 5 days of incubation after the dissolved oxygen to reduce 40 ~ 70% is more appropriate to reduce the amount of too much or too little will bring a large error. Common Problems I. Introduction Biochemical oxygen demand (Biochemical oxygen demand, referred to as BOD) refers to the conditions in the presence of oxygen, microbial decomposition of organic matter in the water in the biochemical process of the mass concentration of dissolved oxygen required to oxygen mg / L said. More organic matter in water, the consumption of dissolved oxygen is more, biochemical oxygen demand is also high. Biochemical oxidation of organic substances, generally divided into two stages, the first stage for the hydrocarbon oxidation of carbon dioxide and water, known as the carbonation stage, at 20 ℃ below 20 days, but at 20 ℃ 5 days up to 68%; the second stage of ammonia is oxidized to nitrite and nitrate, known as the nitrification stage, in order to reach a completely stable state, at 20 ℃ in the need for 100 days or so, due to the longer time. In addition to long-term research work, no practical application value. Microbial activity and temperature, so the determination of BOD, often 20 ℃ as the standard temperature. In order to facilitate the determination of the current domestic and foreign generally 20 ℃ culture 5 days of dissolved oxygen consumption as an indicator, referred to as BOD5. BOD5 that is, take a certain amount of water samples or diluted water samples, culture at 20 ± 1 ℃ for five days, respectively, to determine the water samples before and after the culture of dissolved oxygen, the difference between the two for the BOD5 value. For more product details, please visit Aladdin Scientific website.
Water
BOD Tester Constant Temperature Incubator