Fluorescence Spectroscopy as a Surrogate for BOD (Biochemical Oxygen Demand) in Water Quality Testing: an Example From Fresh Waters and Sewage Effluents From SW England.

The BOD test is regularly used in water quality assessment as a measure of organic load. It takes 5 days, is laboratory based and relies upon the activity of a live microbial community. A more rapid, prescriptive assessment of water quality would allow effective reaction to pollution incidents. Recent developments in fluorescence spectroscopy have provided a rapid (~ 1 min per sample) method for quantifying and characterising the organic matter present in natural waters to ppb levels. This study investigates the relationship between BOD and the fluorescence of organic material (particularly protein-like fluorescence) in natural waters. Samples (n=315) collected across SW England (~ 1,700km2) by the Environment Agency under their regulatory programme, from March 2005-present, have been analysed for fluorescence characteristics and BOD. A good relationship was found between tryptophan-like fluorescence at excitation/ emission wavelengths of 225/350 nm and BOD (r = 0.789) and tryptophan-like fluorescence at excitation/ emission wavelengths 280/350 nm and BOD (r = 0.836). These tryptophan-like fluorophores are believed to be cell wall products and exudates from the microbial community within the samples. This contrasts with a weaker correlation with fulvic-like fluorescence (which correlates closely with total organic carbon and is the soil derived organic fraction of natural waters) at excitation/ emission 240/425 nm and BOD (r = 0.696). It is suggested that fluorescence spectroscopic methods can provide a reliable surrogate for BOD when the correct optical regions are analysed.