Data obtained via online monitoring of chemical parameters
are affected by environmental, process and instrument
related variability. For example, seasonal impacts such as
increased rainfall and algal blooms can affect TOC, conductivity,
pH and turbidity levels. The treatment processes
operated will affect the resultant concentrations of each of
the aforementioned parameters. Finally, the reliability and
sensitivity of the instrument used for measurement will
determine the accuracy of the result. To illustrate, a literature
survey of the variation in TOC concentrations of potable
water and effluent (treated by advanced processes including
membrane bioreactors (MBR), reverse osmosis (RO) and soilaquifer
treatment (SAT)) showed variations of between
0.4–6.6 mg L1 and 0.1–6.7 mg L1
, respectively (Table 1).
Conductivity was also shown to vary significantly between
potable and advanced treated water at between 13–
570 mS cm1 and 65–1240 mS cm1
, respectively (Table 1).
Variations between turbidity, chlorine and pH are generally
much less as these parameters are more easily controlled at
the process level. Overall, based on these reported values, it
appears that TOC and conductivity are most suitable for
detecting cross-connections between potable and recycled
water supplies (Table 1). This conclusion is similar to that
identified for monitoring membrane performance (Adham
et al., 1998; Kumar et al., 2007). Gray (2003) also stated that
online conductivity and TOC measurements are the most
common monitoring technologies for recycled or reclaimed
water systems.