Aquaculture Otelfingen, Switzerland - Production of biomass and cleared wastewater

The aim is to efficiently recycle water-borne nutrients into aquatic biomass, such as floating macrophytes suitable for selling as ornamental plants, fish, phyto- and zooplankton. The research focused on the search for suitable aquatic organisms and their testing at different environmental conditions.

The aquaculture pilot plant Otelfingen is unique in Central Europe. Until today, aquaculture for treating wastewater has almost exclusively been practised in tropical and subtropical areas. This research plant in Switzerland is designed to increase the knowledge gained from applying an approved technology under different conditions, i.e. in milder climate.

Due to high evapotranspiration (average 35 mm/week) and to dilute the biogas-effluent, fresh water had to be added. The hydraulic data and nutrient balance show a good recycling potential.

Input:

• freshwater 53 m3 per week
• biogas-plant effluent 2.5 m3 per week
• 2030 g N per week
• 260 g P per week

Output:

• Water 49 m3 per week
• 950 g N per week
• 4 g P per week

Balance removal by overall system (% of input):

• 53 % N
• 44 % P

Recycling by plant harvest (% of removal):

• 12 % N
• 33 % P

Macrophyte production (and thus nutrient assimilation) was close to theoretical maxima in basins with high nutrient levels (all parameters reported as g per m2):

• Water hyacinth (Eichhornia crassipes) 300 fresh weight , 0.8 N , 0.2 P
• Water spinach (Ipomoea aquatica) 340 fresh weight , 2.0 N, 0.3 P
• Duckweed (Lemna sp., Azolla filiculoides, Spirodela polyrhiza) 220 fresh weight , 0.5 N, 0.2 P

Both plankton and fish growth were only moderately satisfying. The planktonic microalgae and zooplankton culture could be improved if the dark humic substances in the biogas-effluent were eliminated in a pre-treatment. Under given conditions (i.e., temperate climate) fish have only a regulatory function in the ecological production process.

Link to the project and publications:

• http://www.hortikultur.ch [General information, in German]
• http://www.hortikultur.ch/projekte/projektDetail.cfm?id=1 [information about the project, in German]

Wastewater nutrients are not eliminated, but serve as fertilizer - thereby local nutrient cycles can be closed. This wastewater-fed aquaculture mainly serves as a production facility: biomass and cleared wastewater are produced through a controlled aquatic food web. Valuable goods are produced for sale: vegetables, ornamental plants, fodder plants and fish.