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Fenton Process For The Purification Of Polluted Waters

Congress: 2015
Author(s): E. Burcu Ozkaraova Gungor (Samsun, Turkey), Ayse Kuleyin, Feryal Akbal, M. Oya Orkun, Dilek Gižmiž&#;
Ondokuz Mayis University1, Ministry of Youth and Sports2, Sinop University3

Keyword(s): Sub-theme 11: Key vulnerabilities and security risks,
AbstractIntroduction

The Fenton process is based on the production of the highly reactive hydroxyl radical (OH*), which is resulting from the reaction between hydrogen peroxide (H2O2) and ferrous ions Fe(II) under acidic conditions. The oxidation system, which relies on Fenton's reagent, can be employed to treat various types of wastewaters containing a range of organic pollutants like phenols, polycyclic aromatic hydrocarbons, pesticides, formaldehyde, wood preservatives, plastic additives and rubber chemicals. The wastewater treatment using Fenton process results in reduction of toxicity, improvement in biodegradability, odour and colour removal (Bagal and Gogate, 2014).

The treatment of high strength wastewaters with extremely toxic and refractory nature, is mostly an arduous process. The Fenton process can be employed as a post- or a pre-treatment step. In the Fenton process, iron and hydrogen peroxide are the two major chemicals that determine not only the operation costs but also the treatment efficacy (Zhang et al., 2009). The objective of the present investigation was to examine the effectiveness of Fenton process in treating wastewaters of different origins. The performance of Fenton oxidation employed in the treatment of soil washing solution, landfill leachate and phenolic wastewater was investigated with an aim of determining their optimum reaction conditions.

Materials and Methods

Experiments were performed in the batch system. The influence of H2O2, FeSO4 concentrations and reaction time on the removal efficiency were investigated. For the all experiments the pH of reaction mixture was adjusted at the start of the reaction. Required amounts of FeSO4 and H2O2 were added simultaneously into the wastewater/soil washing solution/leachate and then the mixture was shaken using a mechanical shaker. The progress of reaction was followed by monitoring the disappearance of the contaminant and chemical oxygen demand (COD).

Results and Discussion

Treatment of Wastewater from Soil Washing Process

The soil washing solution, which contained a non-ionic aliphatic surfactant, was previously used for the removal of fluorene (Flu) from a contaminated soil. The influence of treatment time, hydrogen peroxide concentration and Fe(II)/H2O2 ratio on the removal efficiency was investigated. Results show that the maximum COD removal (81%) from washing solution was obtained in 4 hours with 2% hydrogen peroxide and a Fe(II)/H2O2 ratio of 1/50. Removal efficiency increased with increasing hydrogen peroxide concentration (0.5-10%) and 100% of the COD was removed with 10% hydrogen peroxide in 2 hours, which was previously selected as the optimum time. The influence of Fe(II)/H2O2 ratio on Flu removal was studied with Fe(II)/H2O2 ratios of 1/15, 1/30, 1/50, 1/100 and 1/200. Removal efficiency increased with higher ferrous iron dosages, which is reflected by greater ratios. About 69% COD removal was achieved within 2 hours with 2% hydrogen peroxide and a ratio of 1/15.

Treatment of Landfill Leachate

High-COD strength landfill leachate was treated with the electro-Fenton process. The COD removal efficiency was investigated at seven different values ranging between 250 and 10000 mg/L at 20 mA/cm2 current densities and 30 min reaction time. It was observed that the COD removal efficiency increased with increased hydrogen peroxide dosage. The optimum COD removal efficiency of 66% was obtained at 5000 mg/L hydrogen peroxide dosage. At this hydrogen peroxide dosage, the energy and electrode consumptions were 0.930 kWh/kg COD and 2.011 kg COD/kg Fe, respectively. The influence of reaction time was investigated ranging between 15 and 60 min at optimum hydrogen peroxide dosage. The COD removal efficiency of 56.25% was obtained at 15 min, which increased to 66%, 70% and 74.21% at 30, 45 and 60 min, respectively.

Treatment of Phenolic Wastewater

The effect of Fe(II) concentration on phenol degradation and COD removal was investigated within the range of 15 and 60 mg/L at phenol concentration of 250 mg/L, hydrogen peroxide dosage of 500 mg/L and pH 3.0. It was found that the removal rate increased with increasing initial Fe(II) concentration. It was obtained that phenol degradation efficiencies were 81.06%, 83.02%, 84.49% and 84.33%, when Fe(II) concentration was 15, 30, 45 and 60 mg/L, respectively. It was obtained that COD removal efficiencies were 58.75%, 60%, 63.75% and 64.38%, respectively. It was also found that no further mineralization occurred after adding more than a 30 mg/L Fe(II) dosage. Therefore, in the next experiments 30 mg/L constant amount of Fe(II) was used.

The effect of hydrogen peroxide concentration on phenol degradation and COD removal was investigated at phenol concentration of 250 mg/L, Fe(II) dosage of 30 mg/L and pH 3. It was obtained that phenol degradation efficiencies were 74.35%, 83.02%, 83.92% and 88.74%, when hydrogen peroxide concentration was 250, 500, 750 and 1000 mg/L, respectively. It was obtained that COD removal efficiencies were 55%, 60%, 60.63% and 65.63%, respectively. The increase in hydrogen peroxide concentration increased the phenol degradation and COD removal.

Conclusion

The results indicated that the Fenton process was successful in the treatment of different wastewaters. Organic pollutants (e.g. phenol, fluorene, etc) were efficiently removed by the Fenton process. Removal efficiency depended on the reaction time and Fe(II) and hydrogen peroxide concentrations. 83% of phenol was degraded and 60% of COD was removed at conditions of 500 mg/L hydrogen peroxide, 30 mg/L Fe(II), 250 mg/L phenol and pH 3.0. Similarly, in the treatment of soil washing solution 40% of COD was removed under optimum conditions, which were 2 hours reaction time, 2% hydrogen peroxide concentration and 1/50 Fe/H2O2 ratio. In the treatment of landfill leachate, a COD removal of 66% was obtained for 5000 mg/L hydrogen peroxide and 30 min reaction time. Bagal, M.V. and Gogate, P.R. (2014). Wastewater treatment using hybrid treatment schemes basedon cavitation and Fenton chemistry: A review, Ultrason. Sonochem. 21, 1-14.

Zhang, H., Choi, H.J., Canazo, P. and Huang, C.P. (2009). Multivariate approach to the Fenton process for the treatment of landfill leachate, J. Hazard. Mater. 161, 1306-1312.

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