Since March 2001 a wastewater treatment pilot plant has been operating on Överjärva Gård in Solna. The pilot plant consists of a combination of treatment steps, e.g. conventional biological processes, hydroponic production of green plants, and tanks with microalgae. Included in the long-term goals for the project were treatment of wastewater with reduced sludge production and chemical usage, and extraction of products from the system.
The system uses pre-denitrification to reduce the nitrogen content; hence the first tank in the pilot plant is an anoxic tank. This tank is followed by an aerated, soil covered tank to filter out odour, and thereafter three aerated tanks for hydroponic growth and nitrification. Within this part of the system, nitrogen and organic matter are reduced to acceptable discharge levels.
To date, the stated goals have been met except regarding phosphorus removal on a year-round basis. The green plants in the hydroponics assimilate some of the phosphorus while they are growing, mainly during summer, but leave a large amount in the effluent water. Fast growing microorganisms are therefore preferred for this purpose, e.g. bacteria and microalgae. The microalgal step, which treats the effluent from the hydroponics, works well during summer when there is a lot of light. To solve this problem, a bacteria-based treatment step during winter is under development.
The microbial processes are followed in the microscope using digital camera.
Wastewater treatment, Plants, Hydroponics, Integrated systems