| Polycyclic aromatic hydrocarbons (PAHs) constitute a large group of aromatic hydrocarbons with two or more fused benzene rings. The PAHs pose a significant risk to human and ecological health due to their toxicity, persistence, mutagenecity and carcinogenicity. Using biodegradation technologies for eliminating PAHs has been considered to be ideal due to their environmental safety and comparatively lower cost. However, biological treatments for PAHs are usually time-consuming and often proved as an incomplete removal process as well. Fenton-like oxidation which can yield strong non-specific oxidant hydroxyl radicals (OH·) that can react with most organic compounds has been regarded as a promising remediation technology for PAH-contaminated aqueous solutions. Therefore, a novel remediation strategy consisting of a sequential biological and Fenton-like oxidation of PAHs from aqueous solution was proposed in this paper.In our previous study, naphthalene was degraded by Bacillus fusiformis (BFN) strain. However, the understanding of degradation of naphthalene is still limited, therefore, in this study, we further explored the process. Results showed that the growth of BFN increased with the concentration of naphthalene increased, eg. When several naphthalene concentrations were 30,50,100 and 200 mg L-1, biomass (OD600) were 0.057,0.081, 0.126 and 0.193, respectively. Nevertheless, the removal efficiency of COD decreased with the increasing the concentration of naphthalene, indicating that naphthalene was used as its sole carbon resource. The biodegradation of naphthalene fitted well to the first-order kinetic model while the growth kinetics of BFN satisfied well to the logistic model. Furthermore, SEM, UV and FT-IR were employed to characterize the degradation of naphthalene. SEM indicated that the morphology of cells grows better in the presence of naphthalene. UV-vis showed that adsorption peak of naphthalene at 276 nm significantly declined after degradation. Finally, FT-IR data demonstrated the new bands at 2878,2930,2968,3438,3667 and 3731 cm-1 were formed, confirming that carboxyl group and phenolic compounds were existed in degraded solution.The effectiveness of bioremediation of naphthalene may be inhibited by its low aqueous solubility, in order to improve the biodegradation of naphthalene by Bacillus fusiformis strain (BFN), this work evaluated the effect of several surfactants (Tween80, SDS, CB, and β-CD) on biodegradation of naphthalene by Bacillus fusiformis strain (BFN), then found out the optimum one for further study. Experiments performed with P-CD showed the highest cell density value (OD600:0.27) and maximum naphthalene removal rate (94.6 %) within 40 h. Thus, the subsequent experiments focused on studying the degradation of naphthalene by BFN in the presence of three cyclodextrins (α,β and γ). Results showed that the order of solubilization of three cyclodextrins is:γ-CD> a-CD>β-CD, and degradation efficiency increased with the order of solubilization.100% of the naphthalene was degraded when the initial y-CD concentration was 0.20mmol L"1.When the initial of naphthalene concentration is 200 mg L-1, within 96 h the elimination rate of COD is only 59.4% with the single technology of biodegradation. However after the 40h of degradation by bacillus fusiformis, the technology of Fenton-like was adopted to improve the degradation rate. And the optimal experiment conditions were as follows: the temperature was 35℃, pH was 3.0, the dosage of H2O2 was 10 mmol L-1, the addition of nZVI was 1.0 g L-1.Under these conditions, the removal of COD reached up to 86.7%. Finally, the overall removal of COD was 91.6% by the combined technology. |
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