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Polycyclic aromatic hydrocarbons (PAHs) are on the list of priority pollutants to be eliminated from the environment due to their carcinogenic and mutagenic action, chemical stability, and resistance to biodegradation. The aim of this study was to evaluate the degradation of fluorene, a well-known PAH, in aqueous solutions (0.03 and 0.08 mg L), by means of a solar-driven conventional (PF) and modified photo-Fenton mediated by ferrioxalate complexes (PFF). Photolysis was also employed for comparison purposes. PF reaction was evaluated at different pH values (2.8, 3.5, and 4.0) and iron concentrations (2, 5, 10, and 20 mg L). On the other hand, PFF studies were conducted at mild pH conditions (4.0, 5.0, and 6.0) and iron content of 2 mg L, keeping initial iron/oxalate molar ratio at 1:3. In both PF and PFF, the initial hydrogen peroxide/iron molar ratio was maintained at 5. In the presence of methanol as cosolvent for fluorene dissolution, the PF reaction was hampered and no consumption of HO was observed during the reaction carried out at constant pH (2.8). This led to low degradation rates, similar to those achieved by photolysis. Under the same pH but using acetonitrile as cosolvent for fluorene dissolution, fluorene degradation was found to be proportional to the iron content used in the PF experiments. On the other hand, at an invariable iron concentration of 5 mg Fe L, the increase in pH was accompanied by a decrease in the molar fraction of the most photoactive iron complex (FeOH) and ferric hydroxides precipitation, leading to a reduction in the fluorene degradation rate. With regard to the PFF tests, similar fluorene degradation performance was achieved at pH 4 and 5, while at pH 6 iron precipitation became relevant and the degradation rate was slightly slower. PFF has shown to be more efficient than the PF under the same pH (4) and iron concentration (2 mg L). Moreover, even at near neutral pH (6), fluorine degradation was shown to be feasible by using ferrioxalate complexes.
Polycyclic aromatic hydrocarbons (PAHs) are on the list of priority pollutants to be eliminated from the environment due to their carcinogenic and mutagenic action, chemical stability, and resistance to biodegradation. The aim of this study was to evaluate the degradation of fluorene, a well-known PAH, in aqueous solutions (0.03 and 0.08 mg L), by means of a solar-driven conventional (PF) and modified photo-Fenton mediated by ferrioxalate complexes (PFF). Photolysis was also employed for comparison purposes. PF reaction was evaluated at different pH values (2.8, 3.5, and 4.0) and iron concentrations (2, 5, 10, and 20 mg L). On the other hand, PFF studies were conducted at mild pH conditions (4.0, 5.0, and 6.0) and iron content of 2 mg L, keeping initial iron/oxalate molar ratio at 1:3. In both PF and PFF, the initial hydrogen peroxide/iron molar ratio was maintained at 5. In the presence of methanol as cosolvent for fluorene dissolution, the PF reaction was hampered and no consumption of HO was observed during the reaction carried out at constant pH (2.8). This led to low degradation rates, similar to those achieved by photolysis. Under the same pH but using acetonitrile as cosolvent for fluorene dissolution, fluorene degradation was found to be proportional to the iron content used in the PF experiments. On the other hand, at an invariable iron concentration of 5 mg Fe L, the increase in pH was accompanied by a decrease in the molar fraction of the most photoactive iron complex (FeOH) and ferric hydroxides precipitation, leading to a reduction in the fluorene degradation rate. With regard to the PFF tests, similar fluorene degradation performance was achieved at pH 4 and 5, while at pH 6 iron precipitation became relevant and the degradation rate was slightly slower. PFF has shown to be more efficient than the PF under the same pH (4) and iron concentration (2 mg L). Moreover, even at near neutral pH (6), fluorine degradation was shown to be feasible by using ferrioxalate complexes.
Purpose This study aims to investigate how NO 3 − reduction affects the migration of NO 3 − in marine sediments and evaluate whether the overlying seawater would be contaminated by NO 3 − injection for in situ bioremediation. Materials and methods The migration of NO 3 − in sandy silt sediment with high acid volatile sulfide (AVS) content and in clayey silt sediment with relatively low AVS content was investigated through column experiments with 5 weeks of incubation. Results and discussion Results showed that NO 3 − reduction through autotrophic denitrification contributed to 93.1 and 48.9 % of total NO 3 − reduction in sandy silt and clayey silt sediments, respectively. In sandy silt sediment with high AVS content, NO 3 − tended to migrate upwards through gas cavities formed during the movement of N 2 gas produced by NO 3 − reduction. Meanwhile, greater NO 3 − consumption by AVS oxidation can effectively prevent the NO 3 − release into seawater. In clayey silt sediment with relatively low AVS content, few gas cavities produced due to insignificant NO 3 − reduction and high density of NO 3 − solution made the downward NO 3 − migration more significant. Without great NO 3 − consumption, NO 3 − from clayey silt sediment was found to be present in the seawater after 5 weeks of incubation.Conclusions Autotrophic denitrification has a significant impact on NO 3 − reduction in marine sediments. The reduction of NO 3 − resulting from autotrophic denitrification can influence its preferential migration path in marine sediment and the possibility of its release into seawater.
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