Demonstrating ecological engineering for wastewater treatment in a Nordic climate using aquaculture principles in a greenhouse mesocosm

Abstract A demonstration plant for ecologically engineered wastewater treatment was constructed in 1989 as an aquaculture inside a greenhouse, i.e., a mesocosm, designed for operation in a Nordic climate, at N Lat. 60°, in Sweden. Located on the Baltic Sea coast in Trosa, Stensund Folk College was used as a model community, with 100 person equivalents (p.e.), for the purpose of developing a recycling concept for the wastewater resources of nitrogen, phosphorus and heat energy. After 4 years of operation, results show that the wastewater from 34 p.e. (0.18 m−3 day−1 person−1) has been treated in the aquaculture, from January 1990 to January 1994. Based on the total wastewater flow from 100 p.e., the nutrient uptake in the aquaculture was 10% of the nitrogen and 8% of the phosphorus. Source separation of phosphorus, i.e., the phosphorus not used, amounted to 34%, coming through an increased awareness to using phosphorus-free cleaning agents. The aquaculture's reduction of pathogenic bacteria and organic material gave a treated effluent close to swimming water quality. Metals were reduced by anaerobic treatment, with 48–73% reduction of the seven identified metals. Energy balances showed a small net energy import during winter, and 19% of the greenhouse's available energy was heat pumped. The costs of aquaculture wastewater treatment still exceed conventional costs, as long as aquaculture products are not counted.