Rensekilden

English summary

An alternative treatment plant in Økosamfundet Dyssekilde

Økosamfundet Dyssekilde is a village community aiming at sustainability, utilizing the values of local communities and acting environmentally correct. In 1991, Økosamfundet Dyssekilde established an alternative waste water treatment plant called Rensekilden. The plant is designed to use the principles of a constructed wetland. The purpose of Rensekilden was to treat the waste water produced in the settlement. The aim was to make a low technology plant based on natural treatment processes. It was to be an exemplary model in order to increase the awareness of waste water and waste water treatment. The costs were to be kept at a minimum both regarding the plant establishment and the working expenses. The work load should be kept at a minimum. It was a wish to utilize the nutrients in the treated waste water in the production of plants. In that way the effluent to the recipient could be minimized.

Before the alternative treatment plant could be established many years of planning had passed. And even then it took several years of negotiation with the authorities before the effluent was allowed to be released to recipient. The authorities set up criteria corresponding to a treatment plant >5000PE. Except for total-nitrogen, which had a modified criterion. This criterion was in accordance with the criterion for phosphorus recommended. The municipality of Hundested is the authority in charge and as such they have engaged Steins Laboratorium to control the effluent to ensure that the criteria are being observed.

The plant is situated on an artificial hill to allow for gravity flow. The waste water runs from the residences to the precipitation tanks by gravity. An electrical pump lifts the water to the top of the hill from where the water flows downhill. The electrical pump is the only installation in the treatment plant that consumes electricity. The consumption of electricity of Rensekilden is 40 % of that of conventional treatment plants per cubicmetre treated water. However, the treatment processes in Rensekilden do not include sludge treatment and only a reduced amount of water from laundry.

In outline the waste water passes two vertical flow beds followed by either a horizontal flow bed with willows Salix sp. or a step with five Virbela flow forms. From the water steps the waste water flows through a covered horizontal flow bed and via a filter bed to a smaller willow bed. From the willow beds the water is released into the recipient. Apart from willow the vegetation of the treatment plant is reeds Phragmites sp. and a few other unidentified herbs.

The efficiency of the plant to remove organic matter is high. The removal of nitrogen is most effective during the summer period. In periods the criterion for total-nitrogen is fulfilled. The demands for ammonia-nitrogen are not fulfilled. The effluent of phosphorus is above the criterion and more or less constant during the year. The oxygen content of the treated water fulfills the demand. There is a reduction of pathogenic indicators comparable to other treatment plants with mechanical-biological treatment.

Originally the dimensioning of the plant was for 60 person equivalents. The amount of people has increased from 26 persons in 1991 to 78 persons in 1997. The amount of water has increased from 2 to 6 m³ per day. In 1997-98 the effluent of organic matter increased, indicating that the maximum load had been reached at that time. In 1999 a new manner of running the plant was introduced. At present the vertical flow beds are constantly loaded increasing the capacity of Rensekilden.

During 1993-1999 the impact of the recipient was negligible as the effluent from Rensekilden is minimal compared to the drainage water the recipient receives from the agricultural fields surrounding it. Since the middle of 1999 the treated waste water is drained to the groundwater. There is a risk of nitrate leaking to the groundwater.

The aim of utilizing the nutrients in the production of plants was never fulfilled. The agricultural department of Økosamfundet Dyssekilde is ecological. The legislation pertaining to ecological farming does not allow the use of waste water as a fertilizer. Only in the treatment plant the nutrients of the waste water is utilized.

Volunteers contributed to the construction and building of the treatment plant. Also the daily running of the plant is performed by voluntary workers. Prizing the work does not increase the expenses to the plant to be unreasonably high. After the establishment of the treatment plant the workload is low. The plant is controlled on a daily basis to discover any disturbances of the treatment. Occasionally the flow direction of the waste water is changed. In the spring and autumn weeding is done throughout the plant.

The value as an exemplary is high. As Rensekilden is raised high above the surroundings, the reeds attract attention and so do the Virbela flow forms with the purling of water. About 10,000 visitors arrive yearly to the alternative community mainly to see the treatment plant. The treatment processes have never failed due to chemicals in the waste water which indicates that the users have a good understanding of the natural treatment processes that rely on microorganisms and plant uptake of nutrients.