Enköping, Sweden is home to an industrial symbiosis network involving the city, municipally controlled services and local farmers and forest owners. Municipally owned combined heat and power plant delivers district heating to the the city and sources most of its fuel from willow locally grown by the farmers and from forest residues and wood chips sourced locally and from the region. The willow farmers, make use of effluents of the municipal wastewater treatment plant as well as sludge from private sewage systems to accelerate the growth of willow.

Following are examples of environmental benefits linked to the synergistic relations in Enköping:
  • Reductions in greenhouse gas emissions: Having a district heating system and a CHP plant fueled almost exclusively by biomass resources enables substantial reductions in CO2 emissions - partly due to increased efficiency and partly due to the substitution of fossil fuels. Locally grown willow further contributes to lowering CO2 emissions by reducing the transort of biomass fuel.
  • Recovery of phosphorus and nitrogen: By using sewage water as fertilizer more than 1 ton of phosphorus is recovered back into the cultivated system every year, which not only reduces eutrophication potential but also reduces the amount artificial fertilizer needed. In a similar fashion, use of nutrient rich effluents and sludge from wastewater treatment operations reduces both the uncontrolled release of nitrogen into the environment and the need for synthetic fertilizers. Through the use of effluents in willow plantations, the WWTP has reduced the nitrogen discharges by 30 t/year–corresponding to a 25% reduction