Kinetics and efficiency of ozone for treatment of landfill leachate including the effect of previous microbiological treatment

The application of conventional physicochemical and microbiological techniques for the removal of organic pollutants has limitations for its utilization on wastewaters as landfill leachates because of their high concentration of not easily biodegradable organic compounds. The use of ozone-based technologies is an alternative and complementary treatment for this type of wastewaters. This paper reports the study of the degradation of landfill leachates from different stages of a treatment plant using ozone and ozone + UV. The experimental work included the determination of the temporal evolution of COD, TOC, UV254, and color. Along the experimental runs, the instantaneous off-gas ozone concentration was measured. The reaction kinetics follows a global second order expression with respect to COD and ozone concentrations. A kinetic model which takes into account the gas liquid mass transfer coupled with the chemical reaction was developed, and the corresponding parameters of the reacting system were determined. The mathematical model is able to appropriately simulate COD and ozone concentrations but exhibiting limitations when varying the leachate type. The potential application of ozone was verified, although the estimated efficiencies for COD removal and ozone consumption as well as the effect of UV radiation show variations on their trends. In this sense, it is interesting to note that the relative ozone yield has significant oscillations as the reaction proceeds. Finally, the set of experimental results demonstrates the crucial importance of the selection of process conditions to improve ozone efficiencies. This approach should consider variations in the ozone supply in order to minimize losses as well as the design of exhaustion methods as multiple stage reactors using chemical engineering design tools.