How to Run an HBOD Test
 

Image	Procedure
	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.
	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.
	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.