Degradation of dimethylphthalate by cells of Bacillus sp immobilized in calcium alginate and polyurethane foam

Abstract

A Bacillus sp. which is capable of degrading dimethylphthalate (DMP) was immobilized in calcium alginate and polyurethane foam for efficient and long term degradation of DMP. Freely suspended cells (10(12) cfu ml(-1)) degraded a maximum of 20 mM DMP. Whereas, alginate-(10(12) cfu g(-1) beads) and polyurethane foam-entrapped (0.34 x 10(6-9) cfu g(-1) foam cubes) cells degraded a maximum of 40 mM DMP within 12-15 days of incubation. Polyurethane foam-entrapped cells degraded 30 mM of DMP at 4 days and alginate-entrapped cells degraded within 10 to 12 days of incubation irrespective of the cell population. When the initial concentration of DMP increased to 50 mM, the DMP degrading ability of the immobilized cells was not increased even after 20 days. Repeated batch cultures by alginate-entrapped cells with initial 35 mM DMP loading could be reused for a maximum of 20 cycles. However, the degradation rate was gradually decreased when the beads were reused for more than 15 cycles. On the other hand, the foam-entrapped cells, with the same initial DMP loading there was no decrease in DMP degrading ability and could be reused for more than 20 cycles. The packed bed reactor with alginate-entrapped cells (I x 10(10-12) cfu g(-1) bead) could be continuously operated for 7-8 days with an initial 25 mM DMP at a flow rate of 50 ml h(-1). Whereas, the polyurethane foam-en trapped cells (I x 10(6-9) cfu g(-1) foam cubes) could be operated continuously for more than 90 days with the same initial DMP loading at a flow rate of 100 ml h(-1). Thus the enhanced degradation of DMP could be achieved by immobilizing the cells of Bacillus sp. in calcium alginate and polyurethane foam as compared to that of freely suspended cells.