This chapter describes the possibility to combine wastewater treatment in recirculating aquaculture systems
(RAS) with the production of crop plants biomass. In an aquaponic RAS established in Waedenswil, Zurich,
the potential of three crop plants was assessed to recycle nutrients from fish wastewater. A special design of trickling
filters was used to provide nitrification of fish wastewater: Light-expanded clay aggregate (LECA) was filled
in a layer of 30 cm in vegetable boxes, providing both surface for biofilm growth and cultivation area for crop
plants. Aubergine, tomato and cucumber cultures were established in the LECA filter and nutrient removal
rates calculated during 42–105 days. The highest nutrient removal rates by fruit harvest were achieved during
tomato culture: over a period of >3 months, fruit production removed 0.52, 0.11 and 0.8 g m2 d1 for N, P
and K in hydroponic and 0.43, 0.07 and 0.4 g m2 d1 for N, P and K in aquaponic. In aquaponic, 69% of nitrogen
removal by the overall system could thus be converted into edible fruits. Plant yield in aquaponic was similar to
conventional hydroponic production systems. The experiments showed that nutrient recycling is not a luxury
reserved for rural areas with litlle space limitation; instead, the additionally occupied surface generates income
by producing marketable goods. By converting nutrients into biomass, treating wastewater could become a profitable
business.
K