Salix vegetation filters for purification of waters and soils

During recent years it has become obvious that it is both environmentally and economically appropriate to use vegetation filters of short rotation willows (Salix spp.) to purify waters and soils. Swedish and Polish experiences of vegetation filter efficiencies have been demonstrated in several laboratory, field lysimeter and full-scale experiments. However, there are still many questions to be answered; for example, how the uptake and allocation mechanisms of heavy metals and recalcitrant organic constituents function, or which maximum doses are possible in a particular situation without any risk of leaching losses. During the past two decades of integrated research in Sweden on plant nutrition it has been demonstrated that willows have the capacity for efficient uptake both of macro and micro nutrients, which is reflected in their high productivity. This paper presents results on how vegetation filter stands of willow, irrigated with municipal wastewater, can function as purification plants while at the same time producing fuel wood. This two-fold utilisation benefits both the environment (e.g. with less air pollution from wood compared with fossil fuels) and the economy (by combining wastewater treatment and fuelwood production). Treatment plants for wastewater purification using various types of vegetation filters have been used both in Poland and Sweden. The Polish experience has been in three sites, namely the Wroclaw experiment, the Zoo at Oliwa near Gdansk, and Turwia near Poznan. In Sweden both nutrient and heavy metal uptake have been followed incorporating the whole process chain from establishment, cultivation and harvesting of the wastewater-irrigated willows to the utilisation of the wood in heating plants.