A Simplified Headspace Biochemical Oxygen Demand Test Protocol Based on Oxygen Measurements Using a Fiber Optic Probe

摘要

Batch respirometric tests have many advantages over the conventional biochemical oxygen demand (BOD) method for analysis of wastewaters, including the use of nondiluted samples, a more rapid exertion of oxygen demand, and reduced sample preparation time. The headspace biochemical oxygen demand (HBOD) test can be used to obtain oxygen demands in 2 or 3 days that can predict 5-day biochemical oxygen demand (BOD_5) results. The main disadvantage of the HBOD and other respirometric tests has been the lack of a simple and direct method to measure oxygen concentrations in the gas phase. The recent commercial production of a new type of fiber optic oxygen probe, however, provides a method to eliminate this disadvantage. This fiber optic probe, referred to here as the HBOD probe, was tested to see if it could be used in HBOD tests. Gas-phase oxygen measurements made with the HBOD probe took only a few seconds and were not significantly different from those made using a gas chromatograph (t test; n = 15, R~2 = 0.9995, p <0.001). In field tests using the HBOD probe procedure, the probe greatly reduced sample analysis time compared with previous HBOD and BOD protocols and produced more precise results than the BOD test for wastewater samples from two treatment plants (University Area Joint Authority [UAJA] Wastewater Treatment Plant in University Park, Pennsylvania, and The Pennsylvania State University [PSU] Wastewater Treatment Plant in University Park). Head-space biochemical oxygen demand measurements on UAJA primary clarifier effluent were 59.9 +- 2.4 percent after 2 days (HBOD_2) and 73.0 +- 3.1 percent after 3 days (HBOD_3) of BOD_5 values, indicating that BOD_5 values could be predicted by multiplying HBOD_2 values by 1.67 +- 0.07 or HBOD_3 by 1.37 +- 0.06. Similarly, tests using PSU wastewater samples could be used to provide BOD_5 estimates by multiplying the HBOD_2 by 1.24 +- 0.04 or by multiplying the HBOD_3 by 0.97 +- 0.03. These results indicate that the HBOD fiber optic probe can be used to obtain reliable oxygen demands in batch respirometric tests such as the HBOD test.