Safe Training Systems Ltd

Rapid portable cross-connection detection by sensitive fluorescence spectroscopy


The implementation of dual reticulation systems for returning recycled water to the home for nonpotable use is now common in new Australian housing developments. Managing the associated public health risk requires consideration of the potential for crossconnections between recycled and potable water pipes. While current protocols for detection exist, they are time consuming and cross-connections have occurred despite their implementation. Cross-connections may occur anywhere from a network to single property scale and hence a highly sensitive, rapid and portable device is required for the detection of contaminated potable water. Fluorescence intensities at ʎex/em=300/350 nm have been previously shown to distinguish recycled water from potable water grab samples with a high degree of sensitivity and reliability using lab-scale equipment. To this end, this paper investigates two potential portable fluorescence systems, describing and discussing the results of in-situ fluorescence analysis programs undertaken at an Australian dual distribution system from the perspective of crossconnection detection.

Population increases and changing weather patterns have caused urban water management in Australia to increase its focus on the sustainability of water resources. As such, water recycling and reuse now play an essential role.

New housing developments are increasingly incorporating dual distribution or third pipe systems, in which wastewater is treated offsite and redistributed back to households as recycled water for non-potable uses such as irrigation and toilet flushing. Within dual distribution systems the potential for cross-connections between recycled and potable water exists (Storey et al. 2007). Cross-connection incidences may damage public confidence in dual reticulation schemes and even present a possible health risk to users, particularly if treatment failure or underperformance occurs. Incidences of crossconnection between potable and recycled water have been documented at Rouse Hill (de Rooy and Engelbrecht 2003; Sydney Water 2004), Newington (Sydney Water 2005) and Pimpama- Coomera (ABC News 2009), and though adverse health effects are yet to be officially attributed to cross-connection incidences in Australia (Storey et al. 2010), the inherent risk remains. In order to minimise this risk a rapid, highly sensitive method of detection is therefore needed to ensure proper management of these networks.

Within the water quality sciences, fluorescence spectroscopy has been investigated in natural, waste and polluted waters (Hudson et al. 2007) and has been utilised to characterise polluted river waters (Baker et al. 2003), to detect tissuemill effluent in rivers (Baker 2002), determine organic matter removal efficiency within water treatment systems (Bieroza et al. 2010) and as a surrogate for biochemical oxygen demand (BOD) measurements (Reynolds and Ahmad 1997; Hudson et al. 2008). The use of fluorescence spectroscopy has also been highlighted as having great potential as a monitoring tool in dual reticulation systems (Henderson et al. 2009) and has been supported by recent investigations into the fluorescence of static grab samples from within an Australian dual reticulation network (Hambly et al. 2010b). This study evaluated a number of water quality parameters for their ability to distinguish recycled water from potable water such as conductivity and dissolved organic carbon, and found fluorescence to have the greatest potential with a typical 10 times distinction. The ability for bench-scale fluorescence analysis to distinguish between recycled and potable water samples has been verified by further studies at a number of other dual reticulation systems across Australia which yielded similar results (Hambly et al. 2010a).

Partial cross-connections may potentially occur within properties, where only limited intrusion of recycled water into potable water supplies occurs. This mixture of recycled and potable water may also vary over time depending on relative water supply pressures and so a high level of sensitivity is paramount in detecting cross-connections with a high confidence level. Monte-Carlo analysis of grab sample fluorescence using strict criteria required a greater than 45% intrusion of recycled water in potable water, whereas conductivity required a minimum of 70% intrusion to achieve the same confidence level (Hambly et al. 2010b). Static mixing of recycled and potable water samples show a linear fluorescence response, making it is possible to identify very low levels of recycled water in potable water.

Hence, the current challenge is to investigate the potential for converting this highly sensitive analytical tool from a bench scale research tool to a portable, engineering tool that is capable of capturing real-time, in-situ data.

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