Monitoring stations in the sewerage network
17 February 2006, News release from Partech Instruments
In order to overcome the problem of the ineffectiveness of sewerage overflows throughout Belgium, some 300 monitoring stations are being installed using sensors developed by Partech for measuring water flows and water quality.
At the end of the 1980s, Belgium was acknowledged to be well behind its neighbouring countries with regard to wastewater treatment. During the following decade an intensive programme of investment was undertaken, particularly at regional level, and by the end of 2002 about 60% of all Flemish households had been connected up to a sewer water treatment installation. With further investment this figure reached about 90% by the end 2004. In addition, the imposition of levies and licenses also encouraged many industrial companies to step up their efforts in terms of improving wastewater and effluent treatment.
As a result of this intensive infrastructure investment there has been a remarkable improvement in the quality of surface water in Flanders. In former days there were an alarming number of watercourses that contained little or no biological life at all. Today more than 55% are only moderately polluted and 13% are qualified either as "acceptable" or "not polluted". All this has had a positive effect in that the Country's ecosystem now contains a greater volume and a more varied selection of aquatic life.
However, the improvements reported in the early part of this decade have not maintained momentum and there has been no further increase in the number of watercourses holding "acceptable" or "not polluted" qualification in spite of ongoing treatment efforts. One of the causes shown to be an obstruction to further improvement is the ineffectiveness of sewerage overflows. In order to gain a clearer picture of this problem the Flemish Environment Society (VMM), the equivalent of our Environment Agency, has started a new monitoring project using field measuring installations on overflows throughout its operating territory.
In common with the UK, the Belgian sewer schemes are generally of the mixed type, in that both effluent and rain water is removed jointly to the treatment installation. In spite of the fact that the sewer scheme is designed to transport a volume equal to six times the average flow at dry weather conditions, some points in the scheme all too frequently come under pressure. In order to prevent surplus wastewater and rainwater from flooding the streets, the flow is directed by means of an overflow construction directly and untreated into the watercourse.
In theory it is estimated that about 4000 overflow constructions in Flanders only become effective during 2% of the time, which represents seven full days a year. In reality some overflow constructions seldom or ever become effective and others are only active when it rains. Besides rain, there are also other factors, such as faulty pump installations, the leaking of groundwater through cracks in the sewerage pipes, watercourses connected to the sewer scheme etc that can have a positive or negative role the actual overflow event.
As it is very difficult to predict an overflow event and given the fact that the event itself is limited in duration, it was necessary to instigate an ongoing measurement campaign over several years. Additionally, there was the problem that the overflow constructions are often located in rural areas far from power and communication supplies, or in urban locations where space is at a premium and vandalism is an issue.
The solution developed by Swedmeter AB and Partech Instruments and supplied by C.R.A.nv uses more than 300 solar powered monitoring stations which employ loggers that can store data locally and transmit the data by means of wireless communication to a central data base. The Swedmeter logger and data communication package is located with the solar power system above ground level whilst Partech Instruments' WaterWatch sondes are underground. In this case the sondes monitor Conductivity and Suspended Solids. Alternative sondes can add pH, Redox, Dissolved Oxygen and Level.
"The WaterWatch sonde is a compact fixed site unit that can contain up to five separate sensors," says Angus Fosten, Partech sales and marketing director. "Contained in a water tight, rugged housing, featuring a self-cleaning facility to reduce maintenance, the sonde provides the ability to measure a wide range of parameters simultaneously," he continues. "Most importantly for remote locations, the instrument has been optimized to require a very low level of power.
Besides giving an indication of the duration of the overflow, each monitoring station also provides an estimation of the actual flow and the degree of pollution of the drained water. Analysis of the collected data will enable VMM to establish a clear picture of these problems and develop appropriate solutions to overcome the problems that they face.
In the city of Leuven, a model based on the sewer system has been developed by the wastewater treatment company Aquafin that allows the introduction of additional parameters, such as the effect of local rainfall and which simulates the behaviour of the sewer scheme. In order to feed the model with real local precipitation data rain gauges are required and certain measuring stations have been equipped with rain gauges financed by the city of Leuven.
The collected data is transmitted to VMM who feed it into the model, which then returns the output to the city's technical department. This is an example of an additional capability that can easily be implemented in the monitoring network and which offers a unique opportunity for VMM, Aquafin and the city of Leuven to share resources and data.
For Partech Instruments, the size and scope of the application is a major confirmation of the capability and reliability of its WaterWatch technology. With some 300 sites now being kitted out, Partech has a sizeable installed base offering considerable potential for demonstrating the performance of its products. The idea has already been picked up in Spain where a number of similar packages are currently being trialed.
For further information please email Partech Instruments