Wetland waste treatment
19 March 2009

The alarming pollution in the brook made Pat and Tony realise that Bridge Farm's waste treatment system was overdue for replacement. Jay Abrahams a real life equivalent of Kelvin, their consultant - explains the sort of system they are considering.

A mature wetland system

As organic farmers, Pat and Tony want to do right by the environment and so have started looking into the different types of natural wastewater treatment systems available. Having considered a conventional reedbed treatment system, Helen has contacted a friend of hers - another cheesemaker - who has an established constructed wetland on her farm.

Instead of wastewater passing through gravel beds, as in a conventional reedbed system, this constructed wetland uses soil as the purification medium, which is planted with a range of wetland plants and willow trees.

The Wetland Ecosystem Treatment or WET System is designed to both absorb and purify the wastewater passing through it, converting it into a beautiful wetland habitat.

The main aims of are:

• The purification of wastewater with minimal non-renewable energy use
• The creation of a beautiful, species-rich ecosystem and wildlife habitat which gives greatly enhanced biodiversity
• The generation of a biomass resource The willow can be coppiced and the harvested wands can be used for a range of traditional and contemporary crafts, or as a biomass fuel

Basis of the system

A WET System is made up of a series of specially designed soil banks and ponds/lagoons. As the wastewater flows through these, it is both purified by microbial action and absorbed by growing plants.




Many plant species are nourished by the farm wastes

Established WET Systems

There are many such systems for domestic sewage. These include systems for full time populations from one person up to 400 people. There is also an environmental education centre, which now has around 250,000 visitors per year, and a field studies centre with a maximum seasonal population of around 200.

A WET System was completed in May 2008 at Fernhill Farm, near Cheddar, which hosts the Big Green Gathering. This system will purify the wastewater from the 50 people who are on site all year round, as well as the 15,000 people who visit the farm for the Gathering.

The willow from this system will be harvested to provide wands for basketry, and fuel for the newly installed biomass boiler, which heats both the farm and camping barns.

Systems have also been used to purify a variety of non-domestic effluents, including a piggery, a dairy farm and a kennels, an organic creamery producing cheese and one producing sheep's milk ice cream, as well as Westons cider mill in Herefordshire, Sheppys cider farm in Somerset and the Otter Brewery in Devon.

Sustainable wastewater purification

WET Systems are "low-entropy systems". They are carbon neutral and use no fossil fuels or electricity to purify the wastewater. They are solar powered - the plants absorb solar energy by photosynthesis. This is in contrast to most conventional wastewater purification systems which, being based upon machines, need a constant supply of energy (electricity) to function.

Low embodied energy

Unlike conventional reedbed treatment systems, no gravel or plastic aeration pipes are used in the construction of this sort of system. Thus gravel does not need to be quarried and transported to the site. Because plastics are not routinely used, the systems have a very low embodied energy. Soil in the root-zone, not imported gravel, is the filtration medium - and this is already on site.





Ecological and Environmental Benefits

A WET System creates a range of wildlife habitats and enhances local biodiversity, providing a refuge for frogs, toads and newts, as well as a large variety of insects and pond life, which in turn attracts many species of bird. Sixty bird species have been recorded on the system at the Westons cider mill.

The CO2 output from conventional mechanical systems is high, due to the materials used in construction, as well as the energy used to operate them. In contrast a WET System absorbs and locks away CO2 in the growing biomass and the soil which is created.

Biomass

The yield from a well managed WET System can include

• one-year old coppiced willow wands for basketry
• two-year old wands for hurdle making or living willow domes and tunnels, as well as the binders used for hedge-laying
• three-year old wands, which are used for the construction of rustic garden furniture and living willow structures

Rapidly growing biomass willow can also be planted. When these are harvested and seasoned, they can be used to fuel simple woodstoves, ceramic stoves or combined heat and power (CHP) boilers, and so contribute to the energy needs of the site.

So if they chose a WET system, as well as treating their waste, Pat and Tony would be producing a resource which they could sell, or use to reduce their energy costs.

Further reading:

More information about WET Systems
These systems are based on the principles of permaculture

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