The Anoxic Degradation Of Typical Polycyclic Aromatic Hydrocarbons In Coastal Sediments

Polycyclic aromatic hydrocarbons(PAHs) are a kind of persistent organic pollutants(POPs), their property of being easily absorbed by soil/sediment results in pollution to the coastal sediment environment. With the advantages of low cost, high efficiency and so on,bioremediation becomes one of the most feasible approaches to controlle PAHs pollution.Anoxic biodegradation of PAHs is a major process in removing PAHs from coastal sediment, because coastal sediment is always in an anoxic state. In this article, three typical PAHs, naphthalene, phenanthrene and pyrene, were chosen as the study objects.With the use of ultraviolet spectrophotometric, their behavior of adsorption and anoxic biodegradation in Bohai coastal zone sediment were investigated. By analyzing the intermediate of degradation, the anaerobic degradation pathways of naphthalene,phenanthrene and pyrene were preliminarily speculated. The degradation bacteria, being isolated and screened from sediment, were identified and studied with their performance of degrading the three kinds of PAHs in anoxic inorganic salt medium and in anoxic sediment.The results revealed that, the behaviors of adsorption of the three PAHs on the coastal sediments all matched pseudo-second-order kinetics, and pyrene was the most easily adsorbed, phenanthrene was the second, and naphthalene was the last. The adsorption process was an exothermic reaction, and the overall was nonlinear, showing that the adsorption including distributional effects and surface adsorption reaction. In the sediments, the anoxic degradation of the three PAHs under natural conditions, showing93.2% of naphthalene was degraded at 30 h, 96.6% of phenanthrene at 7d, 98.1% of pyrene at 42 d. In the anoxic degradation process under natural conditions, two degradation products of naphthalene, two degradation products of phenanthrene and three degradation products of pyrene were detected respectively utilizing GC – MS, and thus the anoxic degradation pathway of naphthalene, phenanthrene and pyrene were preliminarily proposed. Three biodegradable strains of the three PAHs were isolated from coastal zone sediments, being named Jun N、Jun F、Jun B, respectively. Through bacterial physiologicaland biochemical identification and molecular identification, Jun N was identified as Bacillus and Jun F 、 Jun B were identified as Providencia, and for the first time Providencia was found to be able to degrade PAHs in anoxic environment. The anoxic degradation performances of the three strains in the inorganic salt medium and in sediments were investigated. In the inorganic salt medium, the strain Jun N degraded97.6% of naphthalene in 18 h, and in sediments it degraded 72.6% of naphthalene in 48 h.In the inorganic salt medium, the strain Jun F degraded 98.7% of phenanthrene in 18 d, and in sediments it degraded 80.2% of phenanthrene in 24 d. In the inorganic salt medium, the strain Jun B degraded 60% of pyrene in 36 d, and in sediments it degraded 35.5% of pyrene in 36 d. Under the action of natural condition and the strains, the anaerobic degradation processes of the three PAHs were all accord with the first order kinetics reaction.