Domestic wastewater aquaculture, constructed food web, production of biomass, heat for a school building.
Description of the Process
From 1988 to 2000 a unique wastewater treatment system was in operation near the town of Trosa in Sweden: the Stensund Wastewater Aquaculture. The main technical aims of the aquaculture can be summarized as follows: to clean the wastewater from the school Stensund Folkhögskola (100 p.e.); to produce biomass (plants and animals) from wastewater; to provide heat for heating to Stensund Folkhögskola. Apart from these technical goals, the aquaculture was also designed to attract visitors and raise consciousness for wastewater as a resource that can be reused. The inflow consisted of typical domestic wastewater, the only remarkable exception being a relatively high content of copper (Cu). In a settlement tank (step 1), fats and floating stuff were skimmed off and sand sedimented. In the following step 2, anaerobic degradation by fermentation and anaerobic respiration took place, with the aim to remove heavy metals from the water by precipitating them with sulfides. Step 3 was designed for aerobic BOD/COD degradation and nitrification in a so called biofilter. In the following step 4, phytoplankton took up dissolved nutrients and produced biomass - the key element of the following food chain. Step 5 was for zooplankton feeding on phytoplankton washed out of step 4. Steps 6A and C harboured fish. Steps 6B and 7 were hydroponic channels that were initially also used to raise crayfish. Step 8 (flow forms) helped to aerate the outflow. Step 9 finally was an outdoor pond where crayfish and willows were grown on the remaining nutrients of the wastewater.
During a period of 14 years (1987-2000) the wastewater aquaculture served its purpose to demonstrate that wastewater was an important resource. The wastewater aquaculture was integrated in the resource management of the Stensund campus in terms of treated wastewater, biomass production for different purposes and even energy regeneration for heating purposes. The success of the Stensund Wastewater Aquaculture as a concept is a fact and it should not be confused with the task to scale it up to a level to serve a whole campus. In year 2000 the project was closed down by the Folk College who was the formal owner of the project. By then it had served its purpose to train a new generation of students, capacity build water professionals, and to raise awareness among decision makers in both public and private sectors. The aquaculture concept was replicated to serve similar projects in Sweden and abroad.