The BOD test was devised in the early 20th century and selected as an indicator of organic enrichment in water bodies by the U.K Royal Commission on River Pollution in 1908. Subsequently, the method was adopted by American Public Health Association Standard Methods Committee in 1936 as a reference indicator to evaluate the biodegradation of chemicals and hazardous substances.
BOD is defined as the amount of oxygen taken up through the respiratory activity of microorganisms growing on organic material in the sample. The test is conducted in airtight bottles in the absence of light and under a controlled temperature (20°C ± 1°C) for a set time period. The widely employed 5 days interval was selected as this the time taken from source to sea for the longest U.K river. Hence, the parameter provides a measurement of the carbonaceous organic pollution of water that can be degraded biologically and is expressed in milligrams of O2 per litre (see Table 1 for expected levels from a range of aquatic habitats).
Why is it important?
BOD is a key water quality parameter used in a wide range of applications in the water industry and for environmental monitoring:
Challenges to monitoring BOD
Despite the BOD5 test being long entrenched in legislation there are substantial deficiencies associated with it:
It is clear that a move from traditional laboratory testing to in-situ (real-time) monitoring would help to alleviate most of the problems outlined above. It would immediately address points I - III and would help to improve spatial temporal resolution of monitoring that would be directly beneficial to basin managers, water companies and legislators alike.
Proteus the real-time solution for BOD
The Proteus is a new product providing users with a robust, repeatable, low maintenance sensor platform for measuring BOD in real-time. The Proteus is underpinned by comprehensive research exploring the use of in-situ fluorescence as a technique for real-time BOD measurement. The Proteus is a multi-parameter instrument and for standard BOD configuration - a tryptophan-like fluorescence (TLF) sensor, turbidity sensor (see Fig. 2) and thermistor - provide users with real time measurement of reactive dissolved organic matter found in sewage and slurry, negating the need for a 5-day BOD laboratory analysis. Using a robust correction algorithm the tryptophan signal is corrected, in real time, for known interferrants. The result is a repeatable and highly accurate measurement that can provide instantaneous BOD measurement with a simple site specific calibration.
Fluorescence spectroscopy is a selective and sensitive optical technique enabling in-situ, real-time measurement of dissolved organic matter. Molecules absorb light of a specific wavelength and orbiting electrons are excited to a higher energy state .The electrons then emit light of a specific wavelength to return to the base state.
The dissolved organic matter pool can be mapped in optical space based on its fluorescent properties (see Fig. 2). The TLF peak (red) represents a mixture of free amino acids, peptides and proteins. This is associated with microbial activity and human/animal waste contamination. Numerous published studies have correlated TLF with BOD and faecal coliform counts and our site specific or generic calibrations are able to provide users with highly accurate and repeatable BOD measurements (Fig. 3).