The Biosphère's natural wastewater treatment pilot plant


New Technologies
Extensive Treatment Plants
Cleaning Plants
The Plant’s Main Steps
Marshes Under Investigation : Visitors in Action

The Biosphère is the hub of a vast ecowatch network that studies all aspects of water. In keeping with this theme, it was deemed appropriate to incorporate an extensive wastewater treatment technology into its interpretive and educational programs. If the project succeeds, the Biosphère could establish itself as the model for wastewater treatment that is both sustainable and uses a benign, environment-friendly technology. In addition, scientific monitoring of this pilot plant will yield knowledge that is essential to the effective operation of such plants in North American climatic conditions.

New Technologies

Technical and economic considerations favoured the emergence and selection of new technologies, including extensive technologies, to treat wastewater. Traditionally, in standard plants, which are very well adapted to large urban communities most of the time, intensive techniques are used to treat domestic and city wastewater. However, adapting these techniques to less developed entities has proved technically unimpressive and often ineffective to date. Moreover, this technology is generally more expensive than small population centres need or can afford.

Extensive Treatment Plants

Before the first treatment plants were built, wastewater was discharged directly into the environment, polluting lakes and rivers. Today, we know that this practice can be harmful to watercourses, causing algae to proliferate (eutrophication) and habitat quality to deteriorate. Extended treatment plants were developed to take advantage of nature’s purifying capacity using current scientific knowledge. These systems are of quite varied and diverse design. They require relatively large areas of land, which is why they are called "extended." They operate without any electrical or mechanical equipment and with little artificial energy ; the various processes are simply incorporated into semi-developed natural ecosystems (wetlands) or artificial ecosystems.


For part of the year or day, the soil surface is covered by an expanse of shallow water, such as a marsh, swamp, peat bog or aquatic-grass bed, in which many plant and animal species live. It is generally thought, wrongly, that these wetlands are dirty and useless. On the contrary, wetlands are the environment’s kidneys. Their role is to filter and purify river and lake water just as our own kidneys filter our blood.

Cleaning Plants

How can you treat wastewater generated each week by the Biosphère’s users while still respecting nature ? When determining the design parameters of our pilot plant, the designers were subject to two major constraints :

  • hydraulic and pollutant loads generated by the Biosphère’s users, which can cause a wide variation in water flow ;
  • the elimination of any nauseating odours, because of the plant’s location in an urban park that receives lots of visitors.

These considerations were taken into account in the development of the 800 m2 natural wastewater treatment plant. It is made up of three ponds in which species of indigenous plants filter the wastewater as they would naturally in a marsh. For two weeks, the wastewater circulates in the ponds, where it is purified by the plants.

The Plant’s Main Steps

First Step

The trip begins in the septic tank, which receives the Biosphère’s effluent. This is the sedimentation stage, which lasts two to three days. Solid matter settles to the bottom, where it will be treated separately. Floating matter remains on the surface and is drained off so the ponds do not become plugged. Water carrying suspended organic particles goes to a pumping station, which pumps it into the first pond.

Second Step

For approximately six days, the aspirated water lies in a 400 m2 sand pond containing reedgrass (Phragmites australis). This plant was chosen because it remains stable in sand, can withstand harsh weather and is able to oxygenate soil. The water circulates underground, fed under pressure through a perforated longitudinal pipe. This is where purification actually begins. It is a team effort, with the plants acting like a processing plant. They metabolize minerals, absorb oxygen from the air and transport it to the roots, and activate decomposition of organic matter by micro-organisms (fungi, yeasts, bacteria, etc). The microbes, stimulated by rhizomes in the sandy soil, begin aerobic biodegradation. During the mineralization stage, particles of organic substances are broken down into inorganic matter and turned into fertilizers or nutrients (nitrogen and phosphorus compounds), most of which are absorbed by the sandy substrate. The remainder are readily taken up by the plants. However, a small amount of nutrients is carried out of the system in the effluent. The polluted influent is purified by the plants, slowly becoming a cleaner effluent. Once the water has been treated and its unpleasant odour removed, it flows through a pipe installed at the end of the pond and is carried by gravity to a second pond.

According to Harm Sloterdijk, the Biosphère’s scientific adviser and the person in charge of the treatment system, the efficiency of each step is scrupulously measured ; most purification takes place during the second stage, that is, in the first pond. Most of the time, the reed pond is able by itself to meet the discharge objectives. Through scientific monitoring, efficiency can be assessed in terms of the reduction of measured purification parameters. After four years of operation, it is around 80%.

Third Step

The second pond, which is 250 m2 in area, is an ecosystem dominated by broad-leaved cattails (Typha latifolia) and duckweed (Lemna sp.).The grouping together of several plant species duplicates the natural diversity and stability of marshes. It also stimulates the growth of micro-organisms, algae and insects. As in the following pond, there is a permanent layer of water where water circulates on the surface above the soil. For four days, algae and plants absorb nitrates and phosphates while small animals and insects clinging to submerged parts of the plants or floating free feed on organic compounds, making the water cleaner and cleaner. Muskrat lodges, frogs and snails attest to the pond’s significant biodiversity. It is also a staging area for certain waterfowl species in the spring.

Fourth and Final Step

The last pond, which is 150 m2 in area, was colonized by wild iris (Iris versicolor), water mint (Mentha aquatica) and Canada waterweed (Elodea canadensis) in the system’s first year of operation. The pond plays two roles : it completes the removal of nutrients and disinfects and oxygenates the effluent. Water stays in the pond for a minimum of three to four days. In the spring of the first year, the first two plants did not grow as much as expected so they did not take up the space reserved for them and the third plant barely survived to the end of the year. The experts’ preferred explanation for this phenomenon is that not enough nutrients remained in the water to feed the three plants. Since then, a number of plants have invaded the pond : cattails (Typha sp.), common reedgrass (Phragmites communis), yellow flag (Iris pseudacorus) and algae (Chara sp.). Canada waterweed (Elodea canadensis) can also be found.

Finally, at the end of its fantastic voyage through ponds full of aquatic vegetation, the water, from which various pollutants have been removed, goes into the Île Notre Dame treatment system.

In winter, the system operates at a much slower rate. The plants stop growing; bacterial activity still takes place, but is less energetic.


It is clear that this innovative natural technology is efficient and economical. It improves water quality while conserving and restoring the environment. It also fits in with two of the Biosphère’s objectives : sustainable development and greening (green technology). In addition to purifying the water, the Biosphère’s pilot plant will serve as a natural laboratory to increase our understanding of artificial marsh purification techniques.

Furthermore, according to Harm Sloterdijk, "using aquatic ecosystems to treat the wastewater of small cities and towns is a highly attractive possibility. Although we still have a lot to learn about how these systems work, we can now take advantage of nature’s extraordinary capacity to correct some imbalances".

Since last summer, scientific monitoring of the system has gained new momentum after a one-year hiatus, and an ecowatch activity has been developed for the Biosphère’s visitors (see following article).

Bibliographical References

  • Belloui, Samia. Description du système d’épuration des eaux usées de la Biosphère [Description of the Biosphère’s wastewater treatment system]. Under the direction of Doctor Harm Sloterdijk. The Biosphère. August 1996.
  • Michaud, Marie-Hélène, guide assigned to the Biosphère’s marsh : presentation, 1999.
  • Sloterdijk, Harm, Scientific Adviser to the Biosphère : presentation, 1999.
  • Vincent, Gilles. Les capacités naturelles d’épuration des écosystèmes aquatiques [The natural purification capacities of aquatic ecosystems]. Magazine Quatre-Temps. Summer 1996. Vol 20, No 2.



The plant has been in operation since June 5, 1995, when the Biosphère was officially opened.


The following article is excerpted from the last issue of The EcoWatcher, the Biosphère Ecowatch Network’s newsletter :

Marshes Under Investigation : Visitors in Action

by Marie-Hélène Michaud

This activity was created to showcase the Biosphère’s Ecowatch Network. In the summer of 1999, we invited visitors to take part in an activity entitled Marshes Under Investigation. Participants learned about and evaluated the operations of the Biosphère’s natural wastewater treatment system. It uses artificial ponds that duplicate the processes in natural marshes, and the muskrats, waterfowl, frogs, snails and other species living in them attest to the system’s biodiversity.

The activity had two major objectives : to illustrate the importance of wetlands in the environment and to get the Biosphère’s visitors involved in monitoring the treatment system. Since our goal is to encourage visitors to take action to save the environment, this second objective fit in very well with the Biosphère’s mission.

The activity took place outdoors around picnic tables near the treatment system. In this outdoor setting, the activity leader explained how the system works and then invited visitors to analyse the amount of phosphate in the water at four different sampling points to evaluate how well the system was working. Phosphate in a body of water is a significant indicator of eutrophication, which is the result of significant nutrient input and is characterized by a proliferation of aquatic plants. The leader ended the activity by explaining the importance of wetlands and demonstrating that the treatment system is an excellent example of sustainable development and a good illustration of the Biosphère’s philosophy. He also pointed out that this treatment technique could be used by small municipalities that don’t have the means to acquire costly infrastructure or by individuals living in rural areas.


The Biosphère
Created : 2000-01-20
Last update: 2000-09-18
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