Nutrient reuse for biomass energy production

Wastewater is treated in mechanical, biological and chemical steps at Haga central WWTP in the municipality of Surahammar, Sweden, Surahammar Kommunalteknik AB is a publicly owned company, responsible for water and wastewater services as well as for distant heating and waste management in the municipality, In co-operation with VBB Viak consultants and the Department of Crop Production Science at the Swedish University of Agricultural Sciences Surahammar Kommunalteknik AB is looking at the possibilities of innovative solutions for nutrient reuse. The conditions for a systems approach on energy and materials are excellent. Four species of grass was irrigated with supernatant from the sludge digester blended with treated wastewater on a pilot scale 1994-1995. Test runs with co-digestion of ensiled grass and sludge was started during winter and spring 1995 but had to be interrupted due to operational problems. Test runs will be continued during autumn 1995. Starting in summer 1996, wastewater will be used to irrigate 20 hectares (200 000 m(2)) of land close to the Wastewater Treatment Plant (WWTP). The grass will be ensiled at the treatment plant and co-digested with sludge to increase biogas production. Gas production is expected to increase by approximately 60 percent. Biogas is used for electricity and heat production for internal purposes, Biological phosphorus reduction will be tried in the WWTP to limit the use of chemicals for precipitation. Digested sludge will be used to fertilise willow plantations (Salix) on nearby fields. Harvested Salix will be used as fuel in the local heating plant. Depending on the quality of the sludge it may also be used for fertilising of land for food production, Further ashes from the heating plant should in the future be used for fertilising purposes.