ARTICLE

A pilot facility for stormwater retention and cattail production in Geuensee, Switzerland

First experiences with harvesting and use of cattail seeds

By Philippe Wyss, seecon gmbh, Switzerland.
Translation A. Schoenborn

Contact Ph. Wyss:

Philippe Wyss (born 1955), with a degree in cultural engineering from the Swiss Federal Institute of Technology Zurich (ETHZ) and qualifications as a joiner, has a broad basis for things practical and technical. Building on this, he worked in engineering offices and for NGO's in Switzerland, in Africa and in Asia and was thereby able to gain diverse experiences in the planning and managing of projects. Within his diverse activities, biological engineering and natural waste water treatment, or rather waste water use, are of particular emphasis.

Introduction

In 2002, the first Swiss pilot facility for combined stormwater retention and cattail production (= Typha retention facility) in Geuensee started operating.

The facility is a cost-efficient alternative to conventional stormwater retention systems (requiring large earthworks and construction in concrete) and is built to take up the crest of a stormwater flood from sewers or dewatering ditches at Geuensee.

Typha retention facilities are simple, natural buffer areas which take up the water of heavy rainstorm events, delay the release of the water and lead to a partial clarification. Dimensioned appropriately, Typha retention facilities, a type of surface flow wetlands, can also be used as full-fledged wastewater treatment systems. A study on this option in the Swiss context was conducted in Switzerland in 1999.

A multifunctional system

Typha retention facilities are multifunctional systems, which offer other important services in addition to flood protection and stormwater retention, e.g., wastewater treatment and habitat. In Geuensee, the facility offers habitat and a refuge for waterfowl, small mammals, amphibians and various insect species.

Almost all parts of the cattail plant can be utilized for economic purposes. Leafs and seeds can be used as raw material for the production of insulation material.

Concerning the technologies of building and constructing with clay, the seed fibers can also be used as an additive to clay plaster. The resulting clay plaster is smother and easier to handle than comparable clay plaster with other fibers as additives. Chopped cattail leaves also help to reduce the weight of clay bricks. Most experiences with the use of cattail material for the improvement of clay building have been collected in Estonia (see also "Green Shoots in Estonia - the Centre for Ecological Engineering Tartu", Newsletter No. 1/2002).

With the pilot project in Geuensee we wanted to:

• collect experiences with harvesting and processing of cattail for construction with clay under Swiss conditions
• examine the use of cattail as CO₂-neutral fuel (as pellets or in pyrolysis)
• Make cattail better known among Swiss clay construction practitioners
• Optimize harvesting

First experiences with harvesting and processing the seed stands

In the first growing season 2002, the cattails grew rather slowly, resulting in a low number of cattail flowers and seed stands. Therefore, in winter 2002/03 only a few well developed cattail flowers were found and they were not harvested.

In the second growing season 2003, the cattails grew much better, as it was expected (Fig. 4).

2003 was a hot and dry summer in all of central Europe. For the cattails, this led to very early flowering. The first seed stands were ripe in September. Some of them could, therefore, already be harvested at the end of the summer.

The cattail seed stands were harvested manually. Only well-developed seed stands were harvested. They were broken from the top of the stems and collected in baskets. Due to the early harvesting, and since the harvested material couldn't be processed right away, the harvested seeds were packed up in jute bags and stored and dried in a woodshed with low humidity. The second harvest was carried out in February 2004. Harvesting was much facilitated by the dryness of the seed stands then. The second harvest was done in collaboration with clay plasterers, who processed a part of the seeds the same day. On the harvesting day, a bathroom in a new house (a single-family home) was plastered with the clay plaster mixed with cattail seeds (Fig. 5).

Harvesting and processing the remaining cattail stands

Harvesting of the remaining cattail plants was done in March 2004 with a special harvester. The harvester equipped with chains could drive on the top soil of the Typha retention facility without sinking into the ground. The plants were harvested, chopped and loaded on a trailer in one processing step. Then, the material was dried in a grass-drying facility for storage and filled into so called "bigbags". The material will be used in August, 2004 for building a single-family home.

The effects of driving into the cattail field will become visible this summer. Slight compression by chains are known to stimulate the formation of cattail shoots by the rhizomes. We expect that the density of the Typha culture will even be higher. However, in May 2004 (see Fig. 6) the tire tracks were still visible in the culture, even though the cattails had developed quite well since the harvest.

For drying, the Typha chips were further chopped to about half the size and dried afterwards in an oven at 130 degrees centigrade. In comparison to drying grass or corn, oil consumption for drying was rather small, even though harvesting took place during a rain event and the material had been exposed to continuous rain for several hours before being dried.

A small part of the harvested material was used to produce pellets. This small experiment showed that oil consumption for this processsing step is lower than for the production of wood pellets. However, further investigations are necessary, on physical and technical issues as well as on market issues. We think, that in regions with a lack of fuel, the fast-growing and ubiquitous cattail plant could become ecologically and economically important quite fast.