The traditional biochemical oxygen demand (BOD) test was invented around the beginning of the 19th century to determine the strength of wastewaters discharged into rivers. The five-day time period was based on the time of flow of a river (the Thames in England) between London and the sea. It was a simple, yet primitive test that required ground-glass stoppered bottles, wet chemical techniques to measure dissolved oxygen, and wastewater dilutions.
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.
What you need to run an HBOD test
- The HBOD test instructions. Download these instructions written in the format of “Standard Methods”.
- An instrument to measure oxygen, either dissolved oxygen in the water, or oxygen in the headspace.
- You can use an optical oxygen probe that is non-consumptive to measure either the gas or liquid oxygen concentrations. See for example the one made by Ocean Optics.
- A gas chromatograph (GC) can be used to measure oxygen in the headspace. An example of inexpensive GCs are those made by SRI International; their “Educational” GC is relatively inexpensive (~$6,000 in 2017)
- The least accurate, but easiest way, is simply to pour your sample into a small container that can be examined using many different types of dissolved oxygen probes. We have found that this works well due to the high resistance for oxygen transfer from or to a liquid from the air phase.
- Other items
- Air Gage: to measure pressure, temperature and relative humidity, so you can calculate the mass of oxygen in your tube when you seal it. A nice combined barometer is available from Cole Parmer.
- HBOD Tubes, tops, and crimper. For sample, the anaerobic test tubes made by Bellco work well.
- Incubator (to keep samples at 20 deg C during shaking)
- Shaker table that fits inside the incubator
- Supporting information that may be helpful
Dispensing into tubes. No dilution steps are necessary for the HBOD test, and small (28-mL) HBOD tubes are used that take up little space.
First, the wastewater is dispensed into HBOD the tubes. We use a digital dispensette (shown far left), although any standard pipettor works just fine.
The volume of wastewater put in the tube varies depending on the strength of the wastewater (see procedure). For example:
for a raw wastewater (39 to 236 mg-HBOD/L) you would fill to 18 mL;
for low-BOD wastewater (7 to 50 mg-HBOD/L) fill with 23 mL
Cap and shake. The tubes are capped (using a crimper), placed in a test tube rack on their sides (shown upright in figure to left), and then shaken in the dark in an incubator for 2 to 3 days.
Several empty tubes are sealed empty to serve as a oxygen reference.
A single small shaker can hold several racks of tubes, and thus little space is used in an incubator.
Measure. To determine the HBOD, the tubes are removed from the shaker and placed upright. The HBOD probe is calibrated using the empty HBOD tubes.
The HBOD probe is then used to measure the oxygen in the sample. The probe is inserted through the tube septum and oxygen measured in the headspace. Oxygen readings take only a few seconds for each tube.
The HBOD is calculated from the percent oxygen in the sample versus that in the empty tubes using a simple equation.
Logan, B.E., D. Kohler, and B. Min. 2001. A new take on an old test. Indus. Wastewater. 9(2):29-33.
Min, B., D. Kohler, J. Brown, and B. Logan. 2001. Using an HBOD probe to measure biochemical oxygen demand of wastewaters. Keystone Water Quality Manager. 34(4):24-28.
Logan, B.E. and D. Kohler. 2001. Oxygen mass transfer coefficients for different sample containers used in the headspace BOD (HBOD) test. Water Environ. Res.73(1):58-62.
Logan, B.E. and R. Patnaik. 1997. A gas chromatographic based headspace biochemical oxygen demand test. Water Env. Res., 69(2):206-214.
Logan, B.E. and R. Patnaik. 1996. The demise of the standard BOD test? Water Environ. Laboratory Solutions. 3(6):8-10.
Logan, B.E. and G.A. Wagenseller. 1993. The HBOD test: a new method for determining biochemical oxygen demand. Water Environ. Res. 65(7):862-868.
Karanfil, T. and B.E. Logan. 2001. Gas Transfer: measurement of overall oxygen mass transfer coefficients in simulated engineered and natural systems. In: AEESP Laboratory Manual, S.E. Powers, ed. AEESP, Champaign, IL.
Logan, B.E., D. Kohler, and B. Min. 2000. A new method to assess oxygen demand based on the HBOD probe. Proc. 73rd Annual WEFTEC Conference, October 14-18, Anaheim, CA. on CD ROM.
Logan, B.E. and R. Patnaik. 1996. A non-dilution BOD test based on analysis using a gas chromatograph: the GC-HBOD test. Proc. WEFTEC ‘96, the 69th Annual WEF Conference, October 5-9, Dallas, TX., vol. 4, pp. 597-604.
Logan, B.E. 1995. The headspace biochemical oxygen demand (HBOD) test: a new approach for measuring BOD. Proc. Seventeenth Annual EPA Conference on Analysis of Pollutants in the Environment, May 3-5, 1994, Norfolk, VA. U.S. EPA Office of Water, Washington D.C., 821-R-95-008.
Logan, B.E. 1992. The HBOD test: a new method for determining biochemical oxygen demand. Proc. 65th Annual Conference of the Water Environment Federation, September 20-24, New Orleans, LA, Vol. 1, p. 379-388.
Presentations Min, B. and B.E. Logan. 2000. Headspace BOD test. Poster Pres. ABASM Fall Meeting, State College, PA, October 27-28.
Logan, B.E., D. Kohler, and B. Min. 2000. A new method to assess oxygen demand based on the HBOD probe. Pres. 73rd Annual WEFTEC Conference, October 14-18, Anaheim, CA.
Logan, B.E., B. Min, D. Kohler, and J. Brown. 2000. Using an HBOD probe to measure oxygen demands of wastewaters. Pres. CSAWWA/WWOA/CWEA TAC 2000 Conference, August 8-10, Hunt Valley, MD.
Min, B., D. Kohler, J. Brown and B.E. Logan. 2000. Using an HBOD probe to measure oxygen demands of wastewaters. Pres. 72nd Pennsylvania Water Environment Association Annual Conference, June 11-14, State College, PA.
Logan, B.E. and R. Patnaik. 1996. A non-dilution BOD test based on analysis using a gas chromatograph: the GC-HBOD test. Pres. WEFTEC ‘96, the 69th Annual WEF Conference, October 5-9, Dallas, TX.
Patnaik, R. and B.E. Logan. 1996. A non-dilution BOD test based on analysis using a gas chromatograph: the GC-HBOD test. Pres. Arizona Water Pollution Control Federation Meeting, Tucson, AZ, May 2.
Logan, B.E. 1994. The headspace biochemical oxygen demand (HBOD) test: a new approach for measuring BOD. Invited Talk, 17th Annual EPA Conference on Analysis of Pollutants in the Environment, May 3-5, Norfolk, VA.
Logan, B.E. 1992. The HBOD test: a new method for determining biochemical oxygen demand. Pres. Water Environment Federation 65th Annual Conference. New Orleans, LA, Sep. 20-24.
Discussions and Comments
Logan, B.E. 2001. Discussion of “Oxygen mass transfer coefficients for different sample containers used in the headspace BOD (HBOD) test.” Water Environ. Res. 73(4):508.
Logan, B.E. 1997. Reply to comment by Iranpour and Shao on “A gas chromatographic based headspace biochemical oxygen demand test.” Water Env. Res., 69(6):1179-1180.
Logan, B.E. 1995. Reply to the Discussion of A.B. Gupta and A.S. Agnihotri on “The HBOD test: a new method for determining biochemical oxygen demand.” Water Environ. Res., 67(3):377-379.