Simultaneous treatment of toluene-containing gas waste and industrial wastewater by the Fenton process

Abstract

This study reports a new perspective for the simultaneous oxidation of a volatile organic compound (VOC) – a toluene gas stream – and a real industrial liquid effluent by the Fenton's process; for that, a lab-scale bubbling reactor, operating in semi-continuous mode, was used. A parametric study was carried out to evaluate the effect of the aqueous matrix (water vs. real effluent), catalyst species nature (Fe2+ vs. Fe3+), concentration of organic matter in the liquid, and inlet toluene concentration in the gas phase. Their effects in the simultaneous gas-liquid treatment were assessed in terms of the toluene removal (from the gas stream) and wastewater mineralization (removal of dissolved organic carbon - DOC). The presence of organic matter in the liquid phase decreased toluene absorption. However, the simultaneous oxidation in the liquid phase extended the period of absorption until its saturation (and inherently the amount of toluene transferred) while still oxidizing 25% of the organic matter present in the industrial effluent. The application of the Fenton-like (H2O2 + Fe3+) process yielded a slightly reduced toluene transfer as compared to the Fenton one (H2O2 + Fe2+) – ca. 10%, although the overall mineralization has been similar. As expected, increasing the inlet toluene concentration reduces the process duration until liquid saturation, at the same time that a higher accumulation of by-products in the liquid due to oxidation was observed. Finally, a sequential treatment approach was performed, wherein liquid oxidation follows the previous simultaneous gas-liquid treatment, representing a strategy for long term operation, providing an opportunity for further VOC abatement in subsequent cycles. The main compounds resulting from oxidation remaining in the liquid phase after each stage were identified, allowing to close the carbon balance by ca. 80%.