Degradation of industrial waste waters on Fe/C-fabrics. Optimization of the solution parameters during reactor operation.

This study addresses the pre-treatment of toxic and recalcitrant compounds found in the waste waters arriving at a treating station for industrial effluents containing chlorinated aromatics and non-aromatic compounds, anilines, phenols, methyl-tert-butyl-ether (MTBE). By reducing the total organic carbon (TOC) of these waste waters the hydraulic load for the further bacterial processing in the secondary biological treatment is decreased. The TOC decrease and discoloration of the waste waters was observed only under light irradiation in the reactor by immobilized Fenton processes on Fe/C-fabrics but not in the dark. The energy of activation for the degradation of the waste waters was of 4.2 kcal/mol. The degradation of the waste waters was studied in the reactor as a function of (a) the amount of oxidant used (H2O2), (b) the recirculation rate, (c) the solution pH and (d) the applied temperature. With these parameters taken as input factors, statistical modeling allows one to estimate the most economic use of the oxidant and electrical energy to degrade these waste waters. The concentration of the most abundant organic pollutants during waste waters degradation was followed by gas chromatography/mass spectrometry (GC-MS). The ratio of the biological oxygen demand to the total organic carbon BOD5/TOC increased significantly due to the Fe/C-fabric catalyzed treatment from an initial value of 2.03 to 2.71 (2 h). The reactor results show that the recirculation rate has no influence on the TOC decrease of the treated waters but affects the BOD increase of these solutions.

Accelerated photobleaching of orange II on novel (H5FeW12O4010H2O)/silica structured fabrics.

This study addresses the photobleaching (discoloration) and total organic carbon (TOC) reduction of the non-biodegradable azo-dye Orange II with H(5)FeW(12)O(40) in homogeneous solution and on H(5)FeW(12)O(40)/silica-structured fabrics in heterogeneous processes. The H(5)FeW(12)O(40)/silica fabric is able to catalyze Orange II bleaching only under light irradiation. In the dark, long-lived intermediates produced in solution were observed to preclude further degradation. The most efficient polytungstate was selected based on the performance during Orange II photobleaching in the presence of H(2)O(2). The H(5)FeW(12)O(40)/silica fabric needed approximately 60 min to photobleach 85% of an Orange II (0.2mM) solution. The amount of H(2)O(2) and the pH was optimized for the photobleaching of Orange II on the H(5)FeW(12)O(40)/silica fabric. The photobleaching was more efficient as the intensity of the applied light was increased. Repetitive photobleaching cycles of Orange II (0.2mM) on the H(5)FeW(12)O(40)/silica-structured fabric proceeded with the same kinetics, showing the stability of this fabric against oxidative radical attack and the absence of Fe-ions leaching into the solution during Orange II discoloration. The photobleaching times were similar for different concentrations of Orange II suggesting that it is controlled by mass transfer and not by a diffusion-controlled processes. The loading of the silica fabric was determined by elemental analysis to be 7.1% for Fe and 27.2% for W. By electron diffuse spectrometry W-clusters were identified on the silica fabrics and by high-resolution electron microscopy the W-clusters of the catalyst were observed to have sizes between 1 and 2 nm. By X-ray photoelectron spectroscopy, it is observed that the W-oxidation state is higher for the unused catalysts than in the catalyst after Orange II photobleaching. This lends support to a photo-assisted Fenton-like mechanism taking place in the H(5)FeW(12)O(40)/ silica-structured fabrics during Orange II decomposition.