Superior biodegradability mediated by immobilized Fe-fabrics of waste waters compared to Fenton homogeneous reactions

Pretreatment of waste waters of industrial origin has been carried out on structured silica fabrics that have been exchanged with Fe-ions. Evidence is presented that the treatment under light irradiation in the presence of added oxidant (H2O2) and the silica loaded fabric (from now on EGF/(Fe(0.4%)) involves fast recycling of the Fe-ions back on the fabric. Attenuated total reflection infrared spectroscopy (ATRIR) of intermediate products as carboxylic acids indicates very fast degradation on the EGF/Fe(0.4%) fabric without any significant concentration of detectable species in the fabric surface. The catalyst surface is shown by ATRIR not to be blocked due to adsorption of any initial or intermediate product during waste water degradation. Degradation products like anilines, phenols and chlorocarbons were present in lower amounts when EGF/Fe(0.4%) fabric was used as the photocatalyst compared to Fenton reagent added in homogeneous solution under light irradiation. The intermediates were determined in each case by GC–MS. The ratio BOD5/TOC after treatment was enhanced more favorably by the EGF/Fe(0.4%) fabric than by homogeneous Fenton reagent pointing out to higher biodegradability attained by heterogeneous photocatalysis in spite of the fact that TOC reduction was more marked in homogeneous media. The structural features of EGF/Fe(0.4%) surfaces were investigated before and after the photocatalysis of oxalates by high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and gas absorption studies (BET). Fe-clusters of ≤1 nm with a fairly homogeneous size distribution were observed along Fe-silicates on the EGF-silica fabric. The state of the Fe-ion oxidation (XPS) and the pore diameter (BET) were constant during long term photocatalysis providing some evidence for the long term stability of the fabric used.