(438a) Solar-Irradiated Degradation of 2,4-Dichlorophenol by the Iron(III) Oxalate-H2O2/UV Process

The homogeneous photocatalytic Fenton reaction is amongst the foremost Advanced Oxidation Technologies. Under certain conditions, this process enables the conversion of organic pollutants into less toxic, more readily biodegradable substances. It can even cause the complete oxidation of pollutants to carbon dioxide and water, plus inorganic salts of all heteroatoms other than oxygen. With this aim, photochemical reactors based on compound parabolic collectors (CPC) are a promising technology. In this work, the solar-driven photocatalytic process based on Fe(III) oxalate and H₂O₂ was applied for 2,4-dichlorophenol (2,4-DCP) degradation using a pilot-scale batch photochemical reactor, operated with five CPC collectors with Duran glass tubes (29.2 mm internal diameter and 1.4 m long) with a total volume of 5 L. The solar collectors had the following characteristics: 90° semi-angle of acceptance, 1.4 mm optical separation, 1.0 concentration factor, and 0.98 m² total collection surface. The effects of the concentrations of H₂O₂ (9.9-130 mmol/L), Fe(III) oxalate (0.2-1.8 mmol/L), 2,4-DCP (21-550 mg C/L), and surface of photons collection (0.196-0.98 m²) were investigated in detail, by means of a Doehlert multivariate experimental design in multiple levels [1]. Temperature, pH, and dissolved oxygen (DO) concentration were monitored over time with the aid of SensoLyt and TriOxmatic 700 IQ digital sensors, respectively, coupled to the WTW MIQ/S 184 XT measuring system. Global solar radiation was monitored with a Kipp&Zonen CMP3 pyrannometer and a CUV4 radiometer. Samples were analyzed using a Shimadzu TOC-5000A equipment in order to quantify the total organic carbon (TOC) concentration. The experiments were carried out in São Paulo, Brazil (latitude 23°32.0min S) on clear sky days, for which spectroradiometric measurements indicated that irradiation in the UVA-UVB range (280-500 nm) corresponded on the average to about 21% of the total global radiation reaching solar collectors, whilst iron oxalate actinometry [2] indicated an average incident photon flux of 2.4x10^-4 einstein/s. The performance of the photo-Fenton system was very good, with a maximum TOC removal of about 92% for the following conditions: [2,4-DCP]₀=3.5 mmol/L; [H₂O₂]=70 mmol/L; [Fe(III) oxalate]=1 mmol/L; and surface of collection of 0.98 m². Also, DO concentration-time measurements revealed to be a good indicative of the degradation progress. Important cross-effects of the number of solar collectors used, irradiance patterns (i.e., accumulated radiant energy profiles), and initial hydrogen peroxide concentration, have been identified. On the other hand, the characteristics of the photocatalytic reactions enabled to explain the observed smaller importance of the Fe(III) oxalate concentration.

Acknowledgements

The authors thank the support by CNPq (National Council for Scientific and Technological Development, Brazil, Project 475904/2006-0) and FAPESP (São Paulo Research Foundation, Brazil, Project 06/52751-6).

Bibliography

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