Chaetomorpha linum in the bioremediation of aquaculture wastewater: Optimization of nutrient removal efficiency at the laboratory scale

Marine pollution from aquaculture wastewater is a widespread and increasing ecological problem. Algae, with their ability to remove surplus nutrients from wastewater, are a good tool for achieving more sustainable aquaculture. In this study, the capability of different biomasses of Chaetomorpha !Mum and Cladophora prolifera for the bioremediation of nutrient-rich (ammonium, nitrate and phosphate) seawater was compared. The results suggest that 10 g L-1C. linum is an excellent candidate for aquaculture wastewater bioremediation. However, the bioremediation efficiency of C. linum was significantly affected by seasonality, with the greatest performance in nutrient removal exhibited by algae harvested in summer. C. linum harvested in winter and acclimated to lab conditions for two months, significantly improved the removal efficiency of both ammonium and nitrate, while worsening that of phosphate. Irrespective of season and acclimation, the simultaneous presence of ammonium and nitrate in seawater strongly inhibited nitrate removal. Thus, we propose the use of a two-step system, tested at the laboratory scale, in which nutrient-enriched seawater can pass through two different algal ponds. C. linum was able to achieve almost complete removal of ammonium in 24 h in the first step, while the second step improved both nitrate and phosphate removal efficiency. The two-step system is an effective innovation for the use of algae in bioremediation of aquaculture wastewaters.