Cleaner water for Dutch windmill site

Until recently, the World Heritage site of Kinderdijk in The Netherlands had an outdated sewage septic system that could potentially leak into surface water. For hundreds of years the site, including 18th-century windmills, dikes and old farmhouses, has protected the surrounding area from flooding. Now a new Flygt pressure sewage system from Xylem has reduced its environmental impact and increased safety.

By Thessa Lageman

Since UNESCO put Kinderdijk on the World Heritage List in 1997, it has become an important tourist attraction with between 175,000 and 225,000 visitors every year touring the site. Its windmills, pumping stations, reservoirs and water channels were built centuries ago to protect the land, which lies below sea level, from flooding. Though modern pumping stations have taken over the work of the windmills, the site has not been connected to Kinderdijk village’s main sewage system due to the technical difficulties involved.

In 2008, the civil engineering consultancy ADCIM won a contract from the water board for the Rivierenland area (Waterschap Rivierenland) and the Kinderdijk World Heritage Association (Stichting Werelderfgoed Kinderdijk) to manage the project to connect the windmill site to the village’s main sewage system.

Dirk Burggraaf, project manager/advisor for water at ADCIM, says that Xylem was an obvious partner for this project, since the two companies have worked together before and it has “always worked really well.” Burggraaf said that the company was also a good choice because Xylem was already managing the micro pump stations in the adjacent municipality of Nieuw-Lekkerland. “It was a really good fit,” he says.

A new sewage solution

The old sewage system comprised septic tanks that were emptied intermittently by a tanker. If they filled up before that, the wastewater went directly into the surface water. Kinderdijk was one of the last areas in the Netherlands to use this system. “Environmental legislation no longer allows it”, says Alexander Vis, head of Xylem’s Pressure Sewage team in the Netherlands. “Nobody wants this kind of system any more.”

With stricter environmental regulations calling for improved wastewater transportation, pressurized sewage systems have proven to be a safe, flexible and reliable way to move wastewater cost-effectively. A pressurized sewage system (PSS) consists of a collecting tank, a pump and the pipes required to feed wastewater into the sewer main. Last August at Kinderdijk, Xylem began installing a complete pressure sewage network including six Flygt Micro pump stations with eight Flygt MP3068 grinder pumps.

Pressurized sewer systems are ideal in tough topographical conditions, such as with hilly and rocky areas and when dealing with high water tables and very flat land, like at Kinderdijk. A PSS provides effective wastewater transportation at minimum depth, and is a smart economic alternative to gravity feed sewage systems since it costs less to install and maintain.

“It was an unusual project for the contractor,” says Vis, “because there were many regulations that had to be taken into account.” For example, because of high water levels, no drilling or digging could take place in the dikes between November and April, as this could cause weak spots to appear. In addition, if drilling was carried out in the wrong place there was a risk that a dike could collapse.

There were also stringent environmental requirements because Kinderdijk is a World Heritage site and is located in a Natura 2000 area, an EU-designated nature conservation area. “The pipes had to be laid very carefully around the wooden foundations of the windmills, which are hundreds of years old,” says Burggraaf. “And in order not to disturb the waterfowl the work had to be done outside the breeding season and the overwintering period.”

Pump monitoring system

The new system has also reduced the risk of flooding, and prevents wastewater from going into the surface water, explains Alexander Vis. The whole area is equipped with telemetry: if a pump is faulty, a message is relayed directly to the municipality’s central computer. “Previously, somebody had to patrol the whole area by bike. And the warning could quite easily come too late.”

Xylem supplied a pump management and communication system to enable accurate monitoring of the entire installation. Each pump station is equipped with an individual FGC-313 pump station computer and a LON communication module. The communication module ensures that the pump station data is collected in the central APX711 pump station computer, which can then relay all data to the Aquaview control station (SCADA system).

Currently twelve areas at the Kinderdijk site and the tourist toilets have been connected to the main sewage system. The windmills themselves will be connected later after a number of adjustments have been made. The site’s wastewater is now transported safely to a water treatment plant in the nearby town of Alblasserdam.

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