Brussels’ sewers are finally computerised
The city of Brussels’ sewage system has ancient beginnings, but it has taken a modern computerised control system to resolve its flooding problems.Brussels was officially founded in AD979, although local legend tells of the city’s origins at the end of the 6th century, when Saint Gorik built a little chapel on a small island formed by two arms of the river Zenne. Today, Brussels is the capital of the European Union, and the river plays an important part in the city’s long-running battle with sewage flooding in times of heavy rain.
In 1970, more changes were needed because of the city’s transportation needs. Some of the channels were replaced by storm basins because the metro track ran alongside the underground river.
Brussels still relies on some old-fashioned methods for cleaning the 350 kms of its subterranean system. Lauwers explains, ‘The hand-moved carts used for cleaning date from 1870, because the gradient in the tunnels is too low for automated cleaning devices.’ Carts are propelled by water pressure down the channels to scrape dirt from the bottom, but they have to be brought back from the end of by road. It takes up to four months to clean the whole system.
Despite continual modernisation, flooding was still a problem in the lowest part of Brussels. When heavy rainfall combined with high tides in the North Sea and in the Escaut, Dyle and Rupel rivers that join the Zenne, the system was unable to cope. When levels in the Zenne were greater than those in the collector basins, water flowing through the Malbaek channel increased from 0.5 metres³/sec to 20 metres³/sec in just 10 minutes. Waste poured into the cellars of Brussels residents, flooding them with sewage.
‘We had to find a solution to stop the water flowing back from the collectors,’ says Lauwers. ‘We needed a pump station that would evacuate water back into the Zenne. ITT Flygt installed a pump station at Antwerpsesteenweg, which went online at the beginning of 1999.’
Now, when the water level becomes dangerous, the collector flow is automatically eliminated by a closing slide. Immediately, all superfluous water is automatically pumped back to the Zenne until water levels fall.
‘When we were working on the new station, we took the opportunity to install ITT Flygt’s monitoring and control system in the four other existing pump stations and the retention basins, linking them with a resisting data transmission cable,’ says René van Diest, commercial director for ITT Flygt SA. Belgium. Using the existing high-speed communications cables saved money in the networking.
This network, linked to a centralised computer, now monitors water levels and flow speed 24 hours a day. It keeps track of the volume of water pumped and when, and monitors maintenance. Data are collected and analysed overnight and full reports of all activity are produced daily. When there is a problem in the system, alarms are triggered and messages are automatically sent to the operators’ mobile phones and pagers. ‘Previously, we had to go in person to check water levels, but now we can control and manage everything from a central office,’ says Lauwers.
‘For example, in one area under the metro, there is a reservoir that is automatically filled under high water conditions, and needs to be cleaned within 24 hours after being used or we have serious sanitation problems with mosquitoes. Previously, we had to check manually if this overflow had been used so we could clean it without delay, but now the Flygt system alerts us automatically.’
Lauwers adds, ‘We started with only asking ITT Flygt to install a pump station, and then they came back with the idea of linking up the entire system to a real-time controlled supervision network.’
Flygt Monitoring Control units (FMCs) were installed at each of the five pump stations, linked to the centralised computer at the department’s headquarters, using ITT Flygt’s Aquaview SCADA software.
The pump stations use FMC200s and FMC400s, for a maximum of two and four pumps respectively. The retention basins use FMC400s, governed by pressiostats, rather than sensors. An FMC100 controls automatic barriers, which control traffic in different areas at specific times.
The FMCs, equipped with modern PCs-embedded technology, control the pumps’ entire installations. The Aquaview software includes real-time visualisation of the installations and their status of operation, remote control, remote set-points registration and handling of all alarms. It maintains a complete record of operation statistics in reports and trend graphs.