Electro-catalytic ozonation of contaminants in landfill leachate: Optimization by BBD, economic evaluation, mechanism, and reaction pathway

An electro-catalytic ozonation process with ZnO nano-granules as a catalyst (CFR-EC/O-3-UV@ZnO process) was developed to treat raw landfill leachate. LC-MS analysis was applied to determine organic compounds. After CFR-EC/O-3-UV@ZnO process, COD, TOC, BOD5, NH4+-N, P-PO4-3, color, and turbidity were reduced to 90.9%, 89.4%, 89.1%, 89.5%, 87.7%, 99.1%, and 99.7%, respectively under the optimum conditions of 10 g.hr(-1) O-3 dosage, pH 11.0, and 0.006 L.min(-1) flowrate. At the same conditions removal efficiencies of heavy metals (HMs): Cr6+, Pb2+, As3+, Mg2+, B3+, Mn3+, Ni2+, Ba2+, Hg2+, Co2+, Fe2+, and Li+ were obtained 90%, 84.7%, 90%, 99%, 83.7%, 95%, 20%, 75%, 91%, 90%, 78% and 60%, respectively. In spite of high COD and BOD5 removal efficiencies, the process could not remove two organic substances including diphenylamine and 2,2,4-trimethyl-1,3-pentanediol. A high R-2 value of 0.99 demonstrated the accuracy of the selected model. Economic evaluation depicted that the current process cost 0.95 $.m(-3). Finally, this process is suggested for the treatment of landfill leachate with relatively high efficiency.