The elimination of 4-nitrophenol (4NPh) from aqueous solutions by electrooxidation at Pb/PbO2 anodes and biodegradation was investigated. Electrochemically, the process was studied under galvanostatic polarization mode in alkaline media (0.1M NaOH, pH 8.5) at 60°C and as a function of the anodic current density J (J = 10, 20 and 30 mA cm-2) of electrolysis. The biological process was carried out in mineral medium of pH 9 with 4NPh as the only carbon and nitrogen source. The strains chosen for the study were isolated from soils close to contaminated industrial aqueous streams, identified and characterized as Neisseria sp. and Acinetobacter sp. These strains showed to be capable to grow in mineral medium with 4NPh. The cultures were grown aerobically in 200 mL flasks filled with 150 mL of 50 ppm 4NPh mineral medium and stirred in an orbital shaker at 250 rpm at a constant temperature of 37°C and pH 9. Periodical samples were taken in order to measure the absorbance of the solution at a wavelength of 600 nm and, therefore, to analize the growth rate of strains. The removal of aqueous 4NPh by electrooxidation and biodegradation was monitored by UV spectroscopy at a wavelength of 340 nm (400 nm in the electrochemical case) and by liquid chromatography (HPLC) using a Nucleosil 100 C-18 (biological amples) or a µ-Bondesil C-18 (electrochemical samples) column (240 x 46 mm inner diameter, 5µm particle size) and UV detection. The 4NPh elimination from the aqueous solutions as a function of the degradation time is shown in the following figures: (a) for the biological process, (b) for the electrooxidation process. All the kinetic studies showed that in the biological process the 4NPh concentration began to diminish in the first steps of the "lag phase" and is stable in minimum values at the end of the stationary phase. HPLC results have demonstrated that the 4NPh concentration was reduced from 50 ppm to 8.5 ppm in 10.5 h of incubation and to 4.9 ppm after 31 h. By electrooxidation in alkaline media, the most effective 4NPh elimination (97%) was obtained at 60 °C, 20 mA cm-2 and 420 min of electrolysis time, with the production of p-benzoquinone and hydroquinone (52.7 and 15.1%, respectively). Under the latter conditions, an almost complete chemical oxygen demand (COD) removal was attained (fig. b), which suggests a high level of 4NPh mineralization (> 80%), a percentage of 4NPh elimination from the solution greater than 95% and a scarce formation of aliphatic acids (e.g., maleic acid and/or formic acid). From the degradation curves in alkaline media, the UV analyses and/or COD measurements, a complete oxidation of aliphatic acids to form CO2 could be predicted for electrolysis time > 420 min, according to a suggested oxidation pathway.
Comparative Analysis about the Biological and Electrochemical Removal of 4-Nitrophenol from Aqueous Media
MARTINEZ, Carlos Alberto;FERRO, Sergio;DE BATTISTI, Achille
2005
Abstract
The elimination of 4-nitrophenol (4NPh) from aqueous solutions by electrooxidation at Pb/PbO2 anodes and biodegradation was investigated. Electrochemically, the process was studied under galvanostatic polarization mode in alkaline media (0.1M NaOH, pH 8.5) at 60°C and as a function of the anodic current density J (J = 10, 20 and 30 mA cm-2) of electrolysis. The biological process was carried out in mineral medium of pH 9 with 4NPh as the only carbon and nitrogen source. The strains chosen for the study were isolated from soils close to contaminated industrial aqueous streams, identified and characterized as Neisseria sp. and Acinetobacter sp. These strains showed to be capable to grow in mineral medium with 4NPh. The cultures were grown aerobically in 200 mL flasks filled with 150 mL of 50 ppm 4NPh mineral medium and stirred in an orbital shaker at 250 rpm at a constant temperature of 37°C and pH 9. Periodical samples were taken in order to measure the absorbance of the solution at a wavelength of 600 nm and, therefore, to analize the growth rate of strains. The removal of aqueous 4NPh by electrooxidation and biodegradation was monitored by UV spectroscopy at a wavelength of 340 nm (400 nm in the electrochemical case) and by liquid chromatography (HPLC) using a Nucleosil 100 C-18 (biological amples) or a µ-Bondesil C-18 (electrochemical samples) column (240 x 46 mm inner diameter, 5µm particle size) and UV detection. The 4NPh elimination from the aqueous solutions as a function of the degradation time is shown in the following figures: (a) for the biological process, (b) for the electrooxidation process. All the kinetic studies showed that in the biological process the 4NPh concentration began to diminish in the first steps of the "lag phase" and is stable in minimum values at the end of the stationary phase. HPLC results have demonstrated that the 4NPh concentration was reduced from 50 ppm to 8.5 ppm in 10.5 h of incubation and to 4.9 ppm after 31 h. By electrooxidation in alkaline media, the most effective 4NPh elimination (97%) was obtained at 60 °C, 20 mA cm-2 and 420 min of electrolysis time, with the production of p-benzoquinone and hydroquinone (52.7 and 15.1%, respectively). Under the latter conditions, an almost complete chemical oxygen demand (COD) removal was attained (fig. b), which suggests a high level of 4NPh mineralization (> 80%), a percentage of 4NPh elimination from the solution greater than 95% and a scarce formation of aliphatic acids (e.g., maleic acid and/or formic acid). From the degradation curves in alkaline media, the UV analyses and/or COD measurements, a complete oxidation of aliphatic acids to form CO2 could be predicted for electrolysis time > 420 min, according to a suggested oxidation pathway.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
