Continuous versus single H2O2 addition in peroxone process: performance improvement and modelling in wastewater effluents

Abstract

The extension of ozonation up to ozone (O3) doses beyond immediate ozone demand (IOD) completion combined with continuous addition of hydrogen peroxide (H2O2) was studied as potential strategy of treatment aimed to the effective abatement of ozone-resistant micropollutants (MPs) from wastewater effluents. Through experiments involving the continuous addition of H2O2 in a semi-continuous ozone contactor, it was demonstrated that this new approach could lead to a 36% reduction of the overall O3 needs for a constant H2O2/O3 molar ratio of 0.25 compared with single ozonation, representing a 28% reduction in the energy consumption. This improvement, however, was mainly attributed to H2O2 addition during the secondary ozonation stage, where the direct ozone demand becomes less important. The ¿OH-exposure per consumed ozone (ROHO3) calculation demonstrated that larger H2O2/O3 ratios (0.5-1) lead to a little improvement on oxidation performance during the IOD stage, whereas relationships of 0.25 work markedly better during the secondary stage of the process. Moreover, continuous versus total initial addition of H2O2 were compared and the first one showed better performance, with differences in estimated energy costs up to 21%. Finally, and since monitoring the fate of O3-recalcitrant MPs during the process is essential, two different strategies for the real-time control of the O3-recalcitrant MPs fate during the process were tested, one based on the ROHO3 concept and the other on continuous measurements of ultraviolet absorbance at 254 nm (UVA254). They both showed accurate predictions (R2 > 0.96) for different compounds, effluents and processes.