Potassium recovery from vinasse by integrated electrodialysis - precipitation process: Effect of the electrolyte solutions

This study aimed to investigate the influence of four different electrolyte solutions (Na2SO4, MgSO4, K2SO4, and NH4NO3) on electrodialysis (ED) performance for vinasse desalination and nutrient recovery, especially of potassium, for agricultural purposes. The experiments were carried out using a mixed configuration of ion exchange membranes, which utilized a monoselective cationic membrane between the central and cathode concentrated compartments and the other non-monoselective membranes. The solution performance was mainly evaluated in terms of energy efficiency as well as nutrient removal and recovery (Ca2+, K and Mg2+). The chemical equilibrium model Visual MINTEQ was used to estimate the struvite and K-struvite precipitation from the cathode concentrated stream. The MgSO4 and NH4NO3 solutions provided the best conditions for vinasse desalting and subsequent nutrient recovery. When MgSO4 and NH4NO3 were used as electrolyte solutions, 4.4 and 3.9 kg of K-struvite and 0 and 7.3 kg of struvite per m(3) of treated vinasse were estimated to be produced, respectively. The desalted vinasse, with a lower potassium content, can be applied via fertigation at higher rates. Therefore, ED is a promising alternative method for vinasse treatment, reducing the environmental impacts associated with its disposal. Moreover, the integration of ED with precipitation has great potential to produce valuable fertilizer.