ecoreport: Continuous water purification with reuse of purified water

26 April 2016

ecoreport: Continuous water purification with reuse of purified water


Does your business want to purify the used water of its offices? There are several possibilities. Luk Mertens, from Natuur21, adds a new technique: a continuous purifying system with plants, allowing to reuse the water in your company. ecoTips had a talk with Luk.

Read the full article in the April-May 2016 edition of ecoTips:


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Helophytes are plants that transport oxygen to their roots. The bacteria between those roots use that oxygen. It is that oxygen supply that allows them to take on the water pollution. The plants and bacteria even do their jobs during wintertime. However, helophytefilters are not new. Everyone knows the percolation fields, functioning as purification systems. Reed also has its downsides, though. It tends to go its own way, which might very well be next to the basin. After a while, the reed is everywhere. "There are so many different types of helophytes", says Luk Mertens. "Types that are not as invasive and work just as well. Those types add beauty to the landscape and are easier to maintain that regular reed.”


Luk also improved the percolation field system. "A percolation field works fine when the amounts of pollution are consistent. However, a company can have a peak pollution at one moment, and almost none the other. It's hard to obtain good results then."



Luk looked for a way to send the water through the root area more than once. "When the polluted water goes through the purifying material just once, there is a big chance not all the pollution is retained. Therefore, I created a system where the water is purified continuously. The system works via interconnected vessels. When the water goes through the purification system, the same amount of water goes out the other way slowly via a pinch pipe. This way, an important amount of water, cleaned continuously, stays in the system.


"A water purification system can catch the eye and be integrated to its surroundings"


The water from kitchen and toilets does not go straight to the purification system but goes through a septic tank and an aeration tank first. From there, small amounts are brought to the purification system. This also has a positive influence on the plants. With a simple purification system, we notice plants are having a hard time during holiday periods or weekends, as no water is flowing through. This system allows water to be available constantly for the plants, even during droughts."


Instead of dumping the purified water, Luk thought of another solution. The water is removed from below the basin, towards an external pump, and released in buffer wells. The rain water from the roof also goes to those wells. From there, the water travels back to the building and is reused for the toilets. In case of abnormal amounts or extreme rains, the buffer wells enter in spillway mode and the purified water goes to an infiltration well. However, this situation is exceptional.

"Users need to keep in mind to use only biological cleaning products. That is the logical choice", Luk explains. "Before the water re-enters the building, it goes through a smell filter. That way, we are certain that the reused water always stays odourless.  Only the water in the kitchen is tap water. Furthermore, we use highly technological and very powerful, energy-efficient pumps. Business security is our number one concern."



One of the positive consequences of the system is the reduction of water consumption. "Water becomes more and more scarce. Foreign investors even start to invest in water. That indicates that drinking water will only become more scarce, hence more expensive. The water levels are going down fast in our regions. All initiatives preventing us from needing too much fresh water are positive".

The reduction of costs is also a remarkable consequence of the water purification.  "In ten years, the price of tap water has doubled. This system reduces the costs of the company. In this case, we used an existing septic tank before the water goes to the aeration tank. This means you don't have to go for all new installations."



The system is much more than a water purification. It looks like a modern pond with resting spots. "The integration in the surroundings is very important to me", says Luk. "We designed a place where the staff can relax. They can spend their breaks here on sunny days. It looks beautiful and modern, and when the surrounding grasses grow back next to the pond, the integration is complete. I always choose local plants and bushes. In this project, for example, we used holly. Local plants are generally easy to keep and to maintain, and integrate nicely.

It goes without saying that the most important part of a purification system is for it to work. That doesn't mean the system has to be ugly.  A purification system such as this can be an eye catcher and create structure in the surroundings. It has an aesthetic value too. The same goes for the infiltration basins. Traditionally, those are made with very steep banks. In those cases, one has to put fences around it for the safety of the staff and visitors. Not exactly a pretty sight. When I have the space for it, I design an integrated basin with much less steep banks. The safety risk is gone, the results much nicer to look at."


Who is Natuur21?

Luk Mertens started designing and placing water-related projects 25 years ago. Landscape integration, a modern look and an easy to maintain system are always the keys for Luk. He realized many ecological shore protections, infiltration basins and water purification systems.

You can contact Luk on his mobile: +32 (0) 495 50 08 32 

More info on

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Text: Hilde De Wachter

Images: Luk Mertens, Natuur21

Date: 23-04-2016

ecoreport: Continuous water purification with reuse of purified water

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