Unitl now treatment of municipal wastewater in Sweden has mainly consisted of removal of phosphorus and easily biodegradable organic substances. Most of the nitrogen has been released in the water phase to the recipients. The recently introduced legal requirements to remove also nitrogen have encouraged the recirculation approach, meaning that, before chemical phosphorus precipitation, municipal wastewater can be used as an adequate nutrient resource for biomass production. The general aim of this paper is to illustrate a realistic way of handling and utilising this resource in a recirculation system, applying a combination of waste water treatment and biomass production. The economic calculations (based on nitrogen, which is a topical problem at the treatment plants) show that the costs for a conventional technical system for removal of nitrogen and phosphorus in wastewater (70-180 SEK (kgN)(-1)) (1 USD = 6.70 SEK) can allow a good margin for investment, operation and management of an irrigation system for wastewater treatment in willow cultivation. The calculations show that treatment costs in willow cultivations vary depending on type of system and size. Nitrogen application rate also has a major impact on costs. (C) 1997 Elsevier Science Ltd.