Återföring av växtnäringsämnen från avloppsvatten till åkermark
en bedömning av intresset för nya näringsrika produkter
Sewage sludge contains plant nutrients and has earlier been utilised as fertilizer to cropland. Unfortunately not only plant nutrients but also heavy metals, pathogens and organic contaminants tend to accumulate in sludge. The suitability to use sewage sludge in agriculture has therefore been subject to several discussions over the years. The Swedish food industry does no longer accept sludge as fertiliser for Swedish producers.
In 1999 the Swedish parliament accepted several objectives for environmental protection. In order to prevent environmental pollution and further exploitation of the earth crust, one of these objectives confirm that phosphorous from sewage shall be recirculated to arable land. To fulfil this objective the amount of contaminants in sewage sludge and other by-products that shall work as fertilisers to cropland needs to be decreased.
In Hammarby Sjöstad, which is a quarter of the city of Stockholm, there are plans of
building a local waste water treatment work. For Hammarby Sjöstad environmental questions
and circulation of natural resources are in focus. Among other things the residents have plenty of information about how they can reduce the concentration of metals and other unwanted compounds in the sewage. The aim is that the information together with great technology in the waste water treatment work will result in waste products that are sufficiently clean to be brought back to arable land. Two types of fertilizers are produced in Hammarby Sjöstad. One is different types of sludge and the other is different types of concentrates.
The aim of this study was to investigate farmers, the food industries, authorities and other affected operators opinions of the fertilizers from Hammarby Sjöstad. The study revealed that all the involved people found the idea of circulation important. According to low content of heavy metals, the concentrates were of special interest. However, if the food industry shall accept these products it is absolutely necessary to certificate them.