Influence of the chemical composition of smectites on the removal of ammonium ions from aquaculture effluents

Ammonia is the main excretory product of fishes, which in its non-ionized form is toxic to aquatic organisms. The adsorption on solid surfaces is an efficient process for the removal of ammonium from the aqueous medium, and some natural and abundant raw materials of low cost have great potential. The aim of this study was to evaluate the efficiency of three smectite clays in natura, with various chemical compositions such as adsorbents for the removal of ammonium from aquaculture effluents. For the characterization of smectites, we performed analysis through X-ray fluorescence, X-ray diffraction, infrared, scanning electron microscope, and adsorption of nitrogen. Assays on the effect of the adsorbent dosage in removing ammonium ion, standard curve of adsorption with synthetic effluents (contaminated with NH₄ ⁺), and analysis of removal of NH₄ ⁺ from aquaculture effluents through adsorption were performed. In determining the best dosage in efficiency of removal of ammonium ion of each adsorbent, we found for clay 1 the dosage of 7.5 %, for clay 2 the dosage of 4 %, and for clay 3 the dosage of 0.5 %. With the determined dosages, the standard curves of adsorption of the synthetic ammonium solution were made. The time spent stirring the aquaculture effluents with smectites in the range of 1 min–3 h, caused no increase in adsorption. Clay 1 presents the greatest potential for making a chemical filter, it can remove 97.84 % NH₄ ⁺ of an effluent of 20 mg L⁻¹, and does not significantly alter the pH of the effluent.