EVALUATION OF SHORT-TERM BOD METHODS

Efforts have been made for decades to reduce the time required for measuring the 5-day biochemical oxygen demand (BOD5) of wastewater and natural water samples (APHA, 1998). One of the earliest short-term BOD methods was to correlate dilution BOD5 values to chemical oxygen demand (COD) or total organic carbon (TOC). Interest has been shown since the 1940's in using respirometers for making short-term BOD measurements. Generally, low-rate batch respirometric tests have provided about the same measure of BOD in two to three days as that obtained in the dilution BOD test in five days, thus there was not a substantial savings in test time. A number of research investigators have used high-rate respirometric tests in which a single dose of wastewater was added to mixed liquor from an activated sludge process as a basis for short-term BOD tests. In some cases, the net cumulative oxygen uptake is correlated to the dilution BOD5 or is calibrated against an organic ”standard” such as glucose-glutamic acid. A benefit of this method is that the reaction can be completed with a few hours instead of the standard five days. While these high-rate methods are very useful for operational control purposes, none has been accepted widely as a substitute for the standard 5-d dilution BOD.Tests conducted by the authors and other researchers have shown a fundamental basis for using high-rate respirometric tests as a basis for measuring BOD on a short-term basis. In this case, the seed- and dilution-corrected oxygen uptake represents the oxygen required for synthesis of biodegradable wastewater constituents The method is sufficiently flexible that it can be conducted using a number of commercial respirometric instruments. The method can be used on a stand-alone basis or the short-term measurement can be correlated to standard 5-d dilution BOD values of wastewater samples or a standard organic substrate. This fundamentally defensible method for measuring BOD on a short-term basis should have valuable application as a substitute for the 5-d dilution BOD test.