Xylem Analytics (YSI Hydrodata), based in Letchworth Hertfordshire, market a comprehensive range of instruments for monitoring water quality either on-line, in the field or in the laboratory, and the company's parent (YSI) is the world's leading manufacturer of instruments for monitoring the quality of natural water in rivers, streams, lakes, reservoirs, underground and coastal applications.
Mr Darren Hanson
Unit 2 Focal Point Lacerta Court
Thames Water Employs Reservoir Profiler to Reduce Costs
A water quality profiling system from YSI Hydrodata has been installed in the Queen Mother Reservoir near London's Heathrow Airport. The system is able to move through the entire water column taking and recording water quality measurements automatically, thereby helping to improve water management decisions.
London lies in one of the driest parts of Britain, and the average annual rainfall is only 750 mm (30 in), four inches less than Dallas. Thames Water is the largest water company in England, supplying water to around eight million people in London and the Thames valley. Between November 2004 and July 2006, the Thames Water region received only 68% of expected rainfall and has experienced below average levels for every month except one. During June 2006 the city only received 25% of normal rainfall levels.
Naturally, the drought has served to increase focus on the efficient use of water resources and one of the measures that staff at Thames Water have been able to implement has resulted in significant improvements in the efficiency of abstraction, storage and production. This has been facilitated by the installation of new profile monitoring technology coupled with a compressed air mixing system.
The Queen Mother Reservoir was built in 1976. In conjunction with a number of other reservoirs, it fulfils a crucial role in the drinking water supply to the west of London. Reservoirs form an important step in the water supply chain because through sedimentation and natural enhancement of biological quality they represent a low-cost method for water quality improvement and Thames Water therefore has a minimum retention time for reservoir storage of ten days.
Commenting on the new monitoring equipment Terry Bridgman, Field Scientist in the water quality team at Thames Water, says "we have always wanted a technology such as the Profiler because knowledge of water quality throughout the entire column helps to improve decisions on water abstraction. Water can be drawn from different depths and if we know the position of the best quality water we can minimise water treatment costs. For example, if we are able to ensure that the algal load in water supplied to the drinking water treatment plants remains low, we can save costs by optimising the treatment process"
YSI Hydrodata installed the Profiler system in the Queen Mother Reservoir on 2 May 2006 and as a result of the success of the system three further Profilers have been installed at other strategic reservoirs and further installations are planned in the near future. The data that these systems provide will enable Thames Water to not only choose a depth for the abstraction of the best quality water, but also to choose the most appropriate reservoir.
Thames Water's largest drinking water treatment works are generally designed to treat stored water, which will typically have a low turbidity. The Profiler enables companies to analyse water quality data and determine where the areas of low turbidity are. Consequently, continuous monitoring helps to maintain the continuous provision of drinking water.
YSI has launched three types of Profiler - buoy mounted, pontoon mounted or, as is the case in the Queen Mother Reservoir, fixed-site. Each of these is able to take measurements at user-defined intervals throughout any water column up to a maximum depth of 100 metres, recording at minimum intervals of 0.5m. The Profilers are able to interface with any of the YSI multiparameter 6-series measurement sondes and as such offer the opportunity to record a wide variety of water quality parameters. The YSI Profilers can be deployed quickly and easily with the help of the 'Profile Wizard' software and data management and export is achieved with 'ProFile Manager' software.
The multiparameter sonde is automatically lowered and raised throughout the water column by a non-corrosive mechanical winch and drive mechanism located above the water surface. Data can be stored on the sonde's internal datalogger and transferred by any of the latest communication technologies.
The sonde in the Queen Mother Reservoir records Chlorophyll, Dissolved Oxygen, Temperature, pH, Conductivity and Turbidity. However, Thames Water's future requirements will include a sensor for Phycocyanin, which is a good indicator of blue-green algae levels. This will provide useful information to Terry Bridgman and his colleagues because whilst storage improves the turbidity and microbiology of water, algae can have a serious deleterious affect on water quality. At certain times, Thames Water is able to suppress algal growth with 'active mixing' within the reservoir by jets and aeration. Diatom algae levels peak in spring and autumn, and should be detected by the chlorophyll sensor. The blue-green algae peak in mid to late summer, but do not have the impact on filtration that filamentous diatoms do.
Mixing does not suppress diatoms, but does assist with the control of green and blue-green algae. However, this process consumes energy and thereby increases costs. It is therefore important that mixing is employed in a timely and efficient manner, and it is anticipated that the Profiler data may assist in this regard.
In summary, Terry Bridgman says that he and his colleagues have been looking for a way to continuously monitor the entire water column for nearly thirty years and he is delighted that, at last, his search has come to an end.