Improvements of the BOD test have consisted mainly in the development of probes to measure dissolved oxygen. The BOD test is of course still used today. However, it is a time-consuming test that lacks the sophistication of other modern analytical techniques. Because of the need to dilute the wastewater for a BOD test, the degradation rates of biological organic matter is slow and often an accurate measurement of the BOD cannot be made due to poor choice of a dilution volume. Everyone has used a BOD test in the US because they have to, but now there are other options.
Bruce Logan originally developed the headspace BOD (HBOD) test when he realized that with modern improvements in container caps (plastic wasn’t invented in 1906!) and instruments, glass stoppered bottles and wet chemical measurements were no longer necessary to determine a biological oxygen demand of a wastewater sample.
The HBOD test consists of simply sealing a volume of wastewater in a gas-tight tube and then incubating the tube (on a shaker table) for given period of time. In only 2-3 days, an HBOD value identical to that of the 5-day BOD is obtained. The HBOD can be determined from measuring either the oxygen concentration in the air—or in the wastewater-- and calculating the total oxygen used from a mass balance. There is no need to dilute the wastewater. The volume of wastewater added to the tube can be varied to suit the strength of a specific wastewater. The HBOD range of a single tube is much greater than a single BOD bottle dilution, and therefore there is less chance of running the test outside the measurable range. Tube-to-tube variations for the HBOD test are smaller than those for the BOD test, making the HBOD test more precise than a BOD test.
The most significant improvement in the HBOD test recently occurred with the availability of the HBOD Probe. Using this probe, it is now possible to measure the oxygen in a tube headspace in just seconds. An HBOD test could be run with equipment available in most modern laboratories, using a dissolved oxygen (DO) probe or a gas chromatograph (GC). However, the HBOD Probe analysis time is much faster than these other methods (seconds, versus 2-5 minutes for the DO and GC tests) and probe calibration takes only a few minutes using laboratory air.
The HBOD is a type of respirometric biochemical oxygen demand (RBOD)
test and the RBOD test that is now included as a proposed method in Standard
Methods for the Examination of Water and Wastewater. In Europe, however,
RBOD tests are now routinely used for measurement of wastewater strength
instead of a BOD test. If you are interested in finding out more about
the HBOD test, read through this web site and please contact us if you’d
like additional information.