Effect of electrolyte solution recycling on the potassium recovery from vinasse by integrated electrodialysis and K-struvite precipitation processes

Abstract

Brazil is the largest importer of potassium-based fertilizers, with Russia and Belarus accounting for 44% of these imports. However, recent events elevated the risk of disruptions in the global fertilizer trade. Thus, the nutrients recovery from potassium-rich industrial wastewater, such as sugarcane vinasse, can contribute to the conservation of natural resources and a guaranteed supply of the product. In this work, the integration of electrodialysis and chemical precipitation processes was evaluated for sugarcane vinasse treatment, aiming at potassium recovery and electrolyte solution recycling. The electrodialysis cathode concentrate was submitted to chemical precipitation to form K-struvite, while the supernatant from this step was recirculated to the cathode concentrate compartment for the next electrodialysis batch, for a total of 3 sequential electrodialysis-chemical precipitation batches. The electrolyte solution recycling implies a reduction in water consumption in the electrodialysis process. Also, through conducting sequential batches, it is possible to evaluate the number of consecutive times that the supernatant can be reused, maximizing the reduction in water consumption for the recovery of the maximum amount of nutrients, however without harming the electrodialysis performance. The electrodialysis presented stable performance throughout the three batches performed, with potassium removal efficiencies around 76% and recovery around 68%. As for the chemical precipitation step, the removal efficiencies of potassium, phosphorus, and magnesium were 69%, 92%, and 88%, respectively, with no significant differences from the Kruskal-Wallis test between the three batches. From the SEM/EDS and X-ray diffraction analyses, the formation of the K-struvite fertilizer in the precipitates was confirmed, leading to the production of 3.2 kg K-struvite/m3 of treated vinasse. The proposed system was suitable for water saving in the electrodialysis stage, recovery of K-struvite fertilizer, and increase in the vinasse application rate to the soil (equivalent to an increase of 330% in the maximum vinasse application rate), while reducing the costs with wastewater transportation for soil irrigation. Thus, this process integration could help a possible fertilizer supply shortage, reduce environmental impacts and reduce costs regarding the electrodialysis concentrate treatment.