Dilution water should be prepared immediately before use. Phosphate buffer is a key reagent because phosphorus is the limiting nutrient in stimulating growth, so it must be added the day the water is used. Never allow "fish tank" tygon tubing or air stones to come in contact with the water.
Tygon will leach oxygen-demanding material over time and air stones provide an excellent surface for bacterial growth. If they are used, you may inoculate your BOD dilution water with bacteria. If you wish to age your dilution water, do not add the single-use nutrient buffers until the day the water is used. Please note that you should not need to age lab reagent water if it is prepared properly.
Excessive DO depletion in BOD blanks is one of the most common problems that plague all wastewater testing laboratories. The following are the most common causes for excessive depletion in blanks:. Generally, avoid using "grocery store" distilled water. This water is stored in plastic bottles, which can leach oxygen-demanding materials. Some analysts have had great luck using "grocery store" distilled water. If you have good luck with a particular brand, don't change.
However, be aware that you can't control how the water is stored. If the water sits on a shelf for several months in a hot warehouse, it's going to be a problem. Nothing leaches organic matter from plastic like hot water. Try doing a blank using dilution water prepared from a jug of distilled water that has been in the back seat of your vehicle for a week during a particularly hot July! Those that have successfully used "grocery store" water generally have a system.
Some will go directly to the factory and buy fresh water. They then date the water, store it in a cool, dry place and discard the water after it is a certain age e. Bottom Line: Use it if it's working for you; but if it isn't, consider other alternatives.
You should not have to age dilution water — as Standard Methods suggests — if the water is prepared properly. If you have to age to improve quality, you should be concentrating your efforts on improving the preparation process. Avoid using auto-dispensing deodorizers in the laboratory. You may be tempted to use deodorizers because wastewater labs can have a bit of an odor. However, don't use them! They typically use alcohol as a carrier which has a very high BOD. All lab reagent water systems, much like expensive instruments, are prone to problems if they are not maintained properly.
Follow the manufacturer's recommendations for cleaning and disinfecting stills, water polishers and deionizer systems. Simple deionizer systems can work well but can quickly be overgrown with bacteria and mold and can leach organics.
Again, regular scheduled maintenance is the key to keeping a system working optimally. A simple deionizer system can and has worked very well for many laboratories. However, you must use quality virgin or nuclear-grade resins. Don't let a manufacturer talk you into lower quality resins to save money. The dilution of water samples for BOD determination was linked to changes in the environment for microbial growth such as nutrition.
The predation phenomenon between microbial cells was more important with less dilution. BOD 5 increased with the specific amount of inorganic nutrient per microbial mass when the natural water was diluted. When seeding was done for synthetic water samples, the seed volume also affected BOD due to the rate of organic uptake by microbes. BOD 5 increased with the specific bacterial population per organic source supplied at the beginning of BOD measurement. For more accurate BOD measurements, specific guidelines on dilution should be established.
0コメント