Enhanced degradation of naphthalene by immobilization of Pseudomonas sp. strain NGK1 in polyurethane foam
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A Pseudomonas sp. strain NGK1 (NCIM 5120) capable of degrading naphthalene was immobilized in polyurethane foam. The naphthalene-degrading activity of the freely suspended cells was compared with that of immobilized cells in batches in shaken culture and in a continuous culture system in a packed-bed reactor. Increasing concentrations of naphthalene were better tolerated and more quickly degraded by immobilized cell cultures than by free cells. An initial naphthalene concentration of 25 mM was completely degraded by freely suspended cells (4×1010 cfu ml–1) and polyurethane-foam-immobilized cells (0.8–1×1012 cfu g–1 foam cubes) after 4 days and 2 days of incubation, respectively. Free cells degraded a maximum of 30 mM naphthalene after 4 days of incubation with 50 mM naphthalene, and no further degradation was observed even after 15 days of incubation, whereas foam-immobilized cells brought about the complete degradation of 50 mM initial naphthalene after 6 days of incubation. Furthermore, with 25 mM naphthalene, the polyurethane-foam-immobilized cells were reused 45 times over a period of 90 days without losing naphthalene-degrading activity. By contrast, with the same amount of naphthalene, alginate-, agar-, and polyacrylamide-entrapped cells could be reused for 18, 12, and 23 times over a period of 44, 28, and 50 days, respectively. During continuous degradation in a packed-bed reactor, foam-immobilized cells degraded 80 mM naphthalene at a rate of 150 ml–1 h–1. With the same flow rate and 40 mM naphthalene, this system operated efficiently and continuously for about 120 days, whereas the packed-bed reactor with alginate-, agar-, and polyacrylamide-entrapped cells could be operated only for 45, 40, and 60 days respectively. Thus, more efficient degradation of naphthalene could be achieved by immobilizing cells of Pseudomonas sp. strain NGK1 in polyurethane foam, rather than in the other matrices tested.
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