Horizontal subsurface filters (HSF) are able to remove a wide range of contaminants from waste water. The progress of development from a haphazard natural phenomenon to a designed engineering process has continued for around 40 years now and the system enjoys worldwide recognition for it's ability to offer low capital cost, environmentally safe reduction of pollutants to low levels.

In particular wastewater from households, industries and other sources in remote areas can be treated at low cost in this way. The system is also applicable on a much larger scale. In the commissioning stages at this moment (August 2005) is a Rootzone facility treating municipal sewage to the highest standards for reuse as irrigation water for public parklands. The capacity of this system is planned to be 360Kl/day and covers an area of 2500sqm.

Horizontal Reedbed - Brisbane (Aerial Photo inset)

Rootzone Filters have been constructed all over the world for such diverse purposes as wastewater from:

Each design is made to the specific requirements of the project, but standard designs have been developed for more common applications such as domestic waste water.

Through the design the aim is to optimize the conditions for hydraulics and desired microbial activities, hence through an integrated process of biological and chemical activity, mechanical filtration and sorption processes to remove the desired contaminant compounds.

The same processes as those applied in conventional biological, chemical and mechanical treatment plants are also used in HSFs. The difference is that the processes are integrated in a nature based design, which at the same time delivers buffer capacity in the soil volume, allowing the purification performance to remain constant even in heavy rainfall situations.

Newly started rootzone filter at Lessor Office Systems Copenhagen, completed in 1995. The office building which has been built to the state of the art of ecological construction methods is not connected to either the mains water or the municipal sewage system.	The same view in 1999.All the effluent from the toilets, showers etc is treated in the rootzone at the right of the picture and the treated water is used to water the garden at the back of the picture.

Naturally the energy consumption with this system is negligible. The huge energy requirements for operating the aeration requirements of a conventional biological filter are replaced by the solar driven power of oxygen through the root system of the reeds. (Phragmitis Australis)

Many hundreds of such systems have been constructed worldwide in every climate from the tropics to the north of Europe.