Short-term nutrient removal efficiency by Ulva pseudorotundata (Chlorophyta): potential use for Integrated Multi-Trophic Aquaculture (IMTA)

Abstract

Short-term N-NH4+ and N-NO3- removal by U. pseudorotundata under different initial nutrient concentrations and biomass stocking densities, monitoring in parallel photosynthetic parameters obtained by Pulse-Amplitude-Modulation (PAM) Fluorometry of chlorophyll-a and evaluating biomass characteristics (CHN, proteins, carbohydrates) was investigated. The results showed that U. pseudorotundata cultivated under solar radiation in a land-based out-door pilot scale was efficient in removing N-NH4+ and N-NO3- even in concentrations as high as 500 µmol L⁻¹ ensuring complete water remediation in a period of 24 h and in all experimental conditions tested, although differences were observed depending on the stocking density and type of N-source. Treatments with N-NH4+ showed faster N removal than those with N-NO3-, however, treatments with N-NO3- demanded more photosynthetic energy. Part of the ammonium removed in the respective treatments may have been volatilized as a combined effect of the pH increase related to photosynthesis and aeration in the tanks. The results presented here establish the fundamental parameters for the use of U. pseudorotundata as a biofiltering organism for effluents with high concentrations of N-NH4+ and N-NO3-.