Incorporation of ozone-driven processes in a treatment line for a leachate from a hazardous industrial waste landfill: impact on the bio-refractory character and dissolved organic matter distribution

Abstract The current work aimed to evaluate the feasibility of including ozone (O3)-based advanced oxidation processes (AOPs), as an intermediate step, in a multistage treatment system for non-biodegradable sulphur-rich leachate from a hazardous industrial solid waste landfill (HISWL), combining chemical and biological oxidation technologies. O3-based AOPs covered perozonation (O3/H2O2), photo-assisted ozonation (O3/UVC), and photo-assisted perozonation (O3/H2O2/UVC). All O3-driven processes were applied to HISWL leachate directly after sulphur compounds removal via catalytic oxidation and chemical precipitation. Moreover, ozonation was also tested after a sequential coagulation step using ferric or aluminium salts (O3/Fe2+ or O3/Al3+), and O3/H2O2/UVC system was likewise tried after Fe-mediated coagulation targeting photo-Fenton-assisted ozonation (O3/PF). The best-performing treatment train encompassed: (i) catalytic oxidation with H2O2 (stoichiometric amount) under free pH, to convert sulphite and sulphide ions into oxidised sulphur species, including sulphate; (ii) chemical precipitation of sulphate as barite mineral without pH correction; (iii) O3/H2O2 process for ca. 2.1-h (natural pH; room temperature; 3.5 kg O3 and 1.1 kg H2O2 per m3 leachate), to degrade refractory organic matter and improve biodegradability; and (iv) biological oxidation to remove the remaining bioavailable organics fraction. This four-stage approach allowed shifting from a highly recalcitrant wastewater to an effluent in full agreement with the regulation for industrial wastewater discharge into the municipal sewer network. Furthermore, the effectiveness of the O3/H2O2 process over the dissolved organic matter transformation was corroborated by fluorescence excitation-emission matrix and size exclusion chromatography analysis.