Development of Separation Process of Soluble Nutrients from Synthetic Dairy Slurry by Modified Solvay Process

Abstract

There is a huge problem with the reuse of dairy slurry (i.e., liquid fraction of dairy manure) which has a high potential as a fertilizer in Japan. The dairy farmer applies too much dairy slurry to their farm for pasture and meadow, because they have a huge amount of slurry production, resulting in over-fertilizing and also causing a bad odor problem. To overcome these problems, the nutrients should be used for other crops managed by other farmers. This is, however, costly due to transportation and a special machine needed for its application. Furthermore, nutrient salt concentrations of slurry as such is improper. Therefore, the solid fertilizers production process (SFPP) from dairy slurry is proposed to produce ammonium sulfate and potassium chloride as fertilizers, and sodium hydrogen carbonate as a by-product. The objectives of this research are 1) to investigate the effect of temperature on sodium hydrogen carbonate precipitation and 2) to confirm the principle of separated precipitation of sodium and potassium. As a result, precipitation of sodium hydrogen carbonate was observed in the temperature range from 25°C to 50°C. The sodium concentration in precipitation was high at 25°C among the experiments. Then, the sodium removal and potassium recovery processes produced sodium hydrogen carbonate and potassium chloride precipitations separately, without ammonia in the precipitations. The element analysis and XRD analysis supported the existence of the crystals. Finally, the possibility of separate production of potassium fertilizer and sodium salt was confirmed.