Avaliação da precipitação química de estruvita na recuperação de nutrientes a partir de efluente misto

Abstract

The combined treatment of leachate with domestic sewage has been carried out in several countries in order to reduce costs. However, high levels of ammonia from the leachate can compromise the biological treatment system due to its potential toxic effect on microorganisms. Thus, the objective of the study was to evaluate the application of the chemical precipitation technique of struvite in mixed effluent, constituted by the mixture of domestic sewage and landfill leachate, aiming at the removal of ammoniacal nitrogen (N-NH3). For this purpose, mixed effluent was prepared in three volumetric proportions, 1%, 5% and 10%, referring to the volume of leachate present in the mixture. The optimization of the chemical precipitation occurred at a proportion of 5% and in batches, under a reaction time of 10 min, stirring at 120–150 rpm and sedimentation for 30 min, evaluating the pH of the reaction medium and the stoichiometric ratio of the reagents. Other volumetric proportions were also investigated in order to understand the behavior of the optimized condition in different concentrations of leachate. Finally, precipitation tests were carried out operating in continuous flow in an ascending fluidized bed reactor. The experiments were carried out using Mg(OH)2 suspension, an alternative and low cost reagent, as a Mg source and the system was evaluated in terms of N-NH3 removal, total phosphorus (Ptot), and COD. The data underwent treatment and statistical tests at 95% confidence (α=0.05). As a result, it was verified that the increase of the leachate in the effluent constitution resulted in the increase of N-NH3 concentrations. The chemical precipitation of struvite in mixed effluent reached removal of N-NH3 in up to 80.6%, Ptot in up to 72.4% and COD in up to 39.4%, and the optimized condition was obtained with pH=8.5 , Mg:N=1.0 and P:N=1.5. The chemical precipitation of struvite in mixed effluent with 10% leachate showed satisfactory results, however, the proportion of 1% did not show significant removals, possibly due to lower concentrations of ammonia in the system. The Mg(OH)2 suspension provided pH control throughout the precipitation process and continuous flow tests reported N-NH3 removal efficiency above 72% and above 57% for Ptot. Therefore, it can be inferred that the investigated technique has applicability, allowing the combined treatment of landfill leachate and domestic sewage in effluent treatment stations. It highlights the need for complementary studies aimed at evaluating the formation of struvite in multiple stages, in addition to optimizing the process in terms of operational parameters, such as agitation and sedimentation time.