Aquaponic Systems: Nutrient recycling from fish wastewater by vegetable production

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 gm−2d−1 for N, P and K in hydroponic and 0.43, 0.07 and 0.4 gm−2d−1 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.