Compliance Testing for Ocean Outfall Performance Utilising Natural Fluorescence of Effluent in Seawater Mixtures

Water samples were collected from public beaches at Sydney, Australia. The beaches were situated at various distances from the three major shoreline ocean outfalls discharging primary effluent. The samples were tested for faecal conform and faecal streptococci indicator bacteria. The same samples were also analysed for natural fluorescence. Excitation wavelength used was 280 nm and fluorescence emission from seawater effluent mixtures was observed at 445 nm. Indicator bacteria densities correlated well with fluorescence intensities for beach monitoring stations north of Sydney Harbour. Best correlations were observed for the stations situated within 5 kilometres from the outfall. Indicator bacteria densities were not as well correlated with fluorescence intensities for the stations south of Sydney Harbour. However, similar emission spectra were observed for all samples collected from stations both north and south of Sydney Harbour. Nevertheless, indicator bacteria densities for southern stations were observed to be better correlated with fluorescence intensities on particular days. The stations north of Sydney Harbour are believed to be impacted only by the one outfall at North Head. However the system south of Sydney Harbour is more complex. The southern stations are known to be impacted by any, or all of the three major outfalls at Bondi, Malabar, and North Head. Fluorescence can be used to determine effluent concentration in ocean waters where the origin of the effluent is known. There should also be opportunities for the development of fluorescence as an alternative indicator for “real time” public health monitoring of recreational waters.