Experimental design for the evaluation of struvite sedimentation obtained from an ammonium concentrated wastewater

Chemical precipitation of struvite as a technique of ammonium nitrogen (NH₄-N) removal from concentrated wastewater has been shown to be an attractive alternative due to its high effectiveness, reaction rate, simplicity, environmental sustainability and, especially, the application potential of the generated solids for the fertilizer industry. The technique of experimental design has been used in order to identify and evaluate the optimum conditions of chemical precipitation reaction applied in a struvite sedimentation study. The preliminary tests were performed using synthetic effluent with a concentration equal to 500.0 mg N L⁻¹. The stoichiometric ratio Mg:NH₄:PO₄ equal to 1.5:1.0:1.25 and pH equal to 8.5 were taken to be the optimum conditions, where a NH₄-N removal equal to 98.6% was achieved with only 10-min reaction time. This condition has been used to evaluate the struvite sedimentation from synthetic wastewaters, intending to check the optimum conditions achieved by the experimental design in different initial concentrations, 1,000 and 2,000 mg N L⁻¹. The results were typical of a good zonal sedimentation and can be used in the scale up the system.