Animal bone char solubilization with itaconic acid produced by free and immobilized Aspergillus terreus grown on glycerol-based medium.

Cells of Aspergillus terreus, free and immobilized in polyurethane foam, were employed in itaconic acid fermentation processes on glycerol-based media. The purpose was to assess their suitability for animal bone char solubilization and the development of a biotechnological alternative to P fertilizers chemically produced from rock phosphate. Animal bones constitute a renewable source of P that can replace the traditionally used finite, nonrenewable rock phosphate as a P source. Glycerol was an excellent substrate for growth (10.2 g biomass L(-1)) and itaconic acid production (26.9 g L(-1)) by free fungal cells after 120-h fermentation. Simultaneously, A. terreus solubilized the insoluble phosphate to a yield of 23 to 50 %, depending on the particle size and concentration. Polyurethane foam cut into cubes of 0.5-0.6 cm per side, with 0.3 mm pore size and applied at 2.0 g L(-1) proved to be an excellent cell carrier. In repeated batch fermentation, the immobilized mycelium showed a high capacity to solubilize animal bone char, which resulted on average in 168.8 mg L(-1) soluble phosphate per 48-h cycle and 59.4 % yield (percent of total phosphate) registered in the fourth batch.