Recycled water plant monitoring
Date:2011
Location: New South Wales Australia
Purpose: To determine if the SMF4 could be used to monitor the output from a grey water recycling plant and conclusively differentiate the output water between potable and recycled.
Background
STS has had a long history of closely working with academia in the development of portable fluorescence equipment. In particular STS have worked Prof Andy Baker formerly of Birmingham University UK and now of University of New South Wales Australia. Prof Baker is a worldwide expert on techniques using fluorescence detection for the monitoring of water quality and STS had the great benefit of Prof Bakers input into the chemistry behind the design of the SMF4.
The University of Birmingham conducted the first trials of the instrument on local catchments and later in South Africa the results of which confirmed the instruments capabilities both in the lab and the field.
Following this Prof Baker moved to Australia and instigated further research using fluorescence detection to monitor the output from a grey water recycling plant both at the plant and at the end user.
The objective was to assess if the SMF4 could be used as an online monitor to identify any change in water quality coming out of the plant. The plant has two outputs one is potable water the other is a recycled water for use only in secondary applications such as gardening and toilets. Homes in Australia have a dual feed so it is essential that the two supplies are not cross connected.
The aim was to show that the SMF4 could not only differentiate between the two out puts at the plant but also that it could be used in the field to check that the services were correctly connected.
Solution
UNSW selected the SMF4 fluorimeter and its sister instrument the SMF2 (a spectrofluorimeter) to conduct the trials.
Currently fluorimeters suitable for making these measurements are bench top instruments of considerable size and also considerable cost. They are not suitable for taking on site and require a power supply to run them. The STS SMF4 however offers the flexibility of its own internal battery, a rugged design and lightweight under 2 kilos making it ideal for field use. The SMF4 uses a discrete sample placed into a UV cell to make its measurements, other fluorescence based instruments depend on probes to be placed into a water flow – this is not suitable for testing for misconnections.
Testing Regime
The initial trial of the units involved monitoring at the recycling plant. A system was set up that measured the outflow of recycled water from the plant in comparison with the potable water outflow.
As well as monitoring the fluorescence counts the temperature and conductivity was also measured for both water types.
The SMF4’s were set in logging mode using flow cells and run from mains 240V power (although they have their own internal power supply for field work). The instruments were set to log at 5 min intervals.
Over a 4 week period the samples consistently and distinctly showed the difference between potable and highly treated recycled waters, with fluorescence counts of around 500 for potable water and 1800 for recycled water.
The trial was therefore able to positively identify the two different water sources and suggest the technique would be ideally suited to identifying cross connections in the field as well as on site.
Further research showed that fluorescence analysis could positively identify inclusion of recycled water in potable at a percentage of 45% against a percentage of 70% when using conductivity.
Field Trial
The SMF4’s were used to test for misconnections in the field where a survey of 90 homes was conducted. Samples were taken at each property of both the potable water and recycled water to see if any cross connection could be identified.
Of the 90 properties one cross connection was identified – and was later confirmed by the occupants who were apparently aware of the problem – the sample is clearly identifiable from the satisfactory results.
The graph below shows the cross connection marked in Red.
Conclusion
Portable fluorescence is able to quickly and effectively determine cross connections between potable water and highly treated recycled water. The technique is more stable than conductivity which has been shown to be very variable over time and also lends itself to rapid field testing at the end users property.
The SMF4 provides the potential to offer both an early warning system at the water plant through inline monitoring of the outflow to the network and for the easy identification of cross connections. It is essential for water companies to ensure that they are seen to be taking public health seriously and an excellent policy to use preventative measures rather than reactive ones.
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