Delft's invention: a Dutch treat of purified water

The first full-scale Nereda plant, at Ede, installed in early 2005

The international consultancy and engineering group DHV has taken over the patents, and has worked with other Dutch companies on proving the technology, called Nereda, is robust and scaleable, and can be adapted to different wastewater applications.

The result, says Ronald Niermans, the director of patent and licensing at DHV, is that Nereda represents “a real Dutch technology”. The project was funded and supported by the Dutch Ministry of Trade and STOWA, the Dutch Foundation for Applied Water Research.

“We are talking with Dutch technology providers to see how we can collaborate in exporting Nereda,” said Niermans in an interview. “The ambition is make it a real Dutch technology success by pooling the expertise of several partners. That’s why the government is interested. It is a vehicle for Dutch environmental technology to be exported to overseas.”

The key to Nereda lies in the use of highly compacted activated sludge pellets. These pellets contain bacteria that break down the organic components in the waste, leaving pure water. In contrast to conventional pellets, which are very flaky and take time to settle, the Nereda pellet sludge settles faster. This makes it possible to dispense with the final stage in the purification process employed in conventional plants where sediments are left to settle in large tanks before the purified water is drained off. In the Nereda system this takes place in the bioreactor.

The innovative step is persuading the bacteria to form pellets. The TU Delft researchers have uncovered the precise process conditions under which bacteria discharge an adhesive material that causes them to clump together.

“Conventionally quite a large space is needed for treatment plants, but with the technology we have developed is possible to build them on plots up to 75 per cent smaller. Not only that, but the cost of building Nereda plants is at least 20 – 30 per cent lower,” said the inventor of the technology, TU Delft professor Mark van Loosdrecht in a separate interview.

This will be a major benefit for Dutch treatment plants, which are reaching full capacity and have little room to expand. In common with urban areas elsewhere, plants tend to be in built-up areas where land is scare and prices high. Nereda plants (named after the water nymph Nereda, daughter of the Greek sea god Nereus) are also compliant with increasingly stringent EU rules water quality.

A trial plant was built at a wastewater plant in Ede at the end of 2003, and the first full-scale plant was installed at VIKA, a cheese manufacturing company, also in Ede, in 2005. A large-scale demonstrator plant is due to come on stream within the next month at the city of Almere.

 “Negotiations for six other plants are ongoing. The technology has taken off faster than I expected,” said van Loosdrecht.

There are about 20 municipal treatment plants in the Netherlands that could be benefit from using Nereda, according to Niermans.  DHV expects it will take the next two years push the technology out across the Netherlands to 10 municipal plants and about 50 smaller industrial plants. The firm also intends to export Nereda to countries including Japan, China, South Africa, Portugal and India.

“We are looking first in countries where we have subsidiaries,” said Niermans. “Initially, we only want to roll out in countries where we have good networks, to make sure we maintain control of the technology.”

And van Loosdrecht summarises. “I think this is a very nice example of a university invention which is quickly operating at full scale, and also of a very intense collaboration between the university and company to put it into practice.”