The Treatment of Aquaculture Wastewaters—A Botanical Approach

The wastewater from freshwater fish farming is responsible for nutrient enrichment in receiving waters. This frequently causes localised problems for the management of the freshwater environment. Conventional wastewater treatment systems are costly to install and operate. This paper investigates the potential of an alternative system. Untreated wastewater from a recirculation system used to culture fish was passed through three treatment systems containing different species of aquatic macrophyte:Rorippa nasturtium-aquaticum(the emergent system);Azolla filiculoides(Lam) (the free floating system); and,Elodea nuttallii(Planch.) (the submersed system). Concentrations of ammonia-N, nitrate-N and phosphorus in all three systems was significantly reduced compared to untreated wastewater during both weekly and twenty four hour sampling regimes. The role played by microbial and bacterial populations in comparison to direct uptake by plants is discussed, as are the implications for system design. The importance of plant cropping, especially in the emergent system, is highlighted as is the potential for use of such a system in environmental management.