Research and engineering assessment of biological solubilization of phosphate

Abstract

This research and engineering assessment examined a microbial phosphate solubilization process as a method of recovering phosphate from phosphorus containing ore compared to the existing wet acid and electric arc methods. This activity was initiated in 1987 as an element of the Office of Conservation and Renewable Energy's Energy Conservation and Utilization Technology Program and has been supported by the public sector for its duration. A total of 860 microbial isolates, collected from a range of natural environments were tested for their ability to solubilize phosphate from rock phosphate. Based on this screening of microorganisms, a bacterium (Pseudomonas cepacia) was selected for extensive characterization and evaluation of the mechanism of phosphate solubilization and of process engineering parameters necessary to recover phosphate from rock phosphate. These studies found that concentration of hydrogen ion and production of organic acids arising from oxidation of the carbon source facilitated microbial solubilization of both pure chemical insoluble phosphate compounds and phosphate rock. Genetic studies found that phosphate solubilization was linked to an enzyme system (glucose dehydrogenase). Process-related studies found that a critical solids .density of 1% by weight (ore to liquid) was necessary" for optimal solubilization. An engineering analysis evaluated the cost and energy requirements for a 2 million ton per year sized plant, whose size was selected to be comparable to existing wet acid plants. The water handling and holding requirements made the conceptual bioprocess plant uneconomical. An optimized process was postulated based on increasing soluble phosphate concentration from 200 mg/L to 20,000 mg/L. The optimized process was shown to be feasible and comparable in energy consumption to that of the wet acid process, lt was considerably less energy intensive when compared to the oxidation method. Based on the findings of this study, a research plan was developed for future phosphate solubilization research.