| The final discharge point for collected landfill leachates is frequently the local municipal wastewater treatment facility. The salinity, color, and/or nutrient and organics contamination of leachates often necessitate some form of pre-treatment. When advanced oxidation processes (AOPs) are considered for pre-treatment, the unique composition of dissolved organic matter (DOM) and the relatively high concentrations of some inorganic solutes in leachate will inhibit treatment efficiency. The most important benchmark for design of AOPs is the expected steady-state production of free radical (·OH). Without a quantitative assessment of total ·OH consumption in high-strength waste water, like a landfill leachate, efficient AOP treatment is uncertain. For this reason, two landfill leachates, distinct in color, DOM, population served by municipal solid waste facility, and age of landfill, were characterized for ·OH-scavenging using a well-established competition kinetics method. After stripping the samples of inorganic carbon, the DOM in leachate from mature (stabilized) landfill was found to react with ·OH at a rate of 9.76 x 108 M-1s -1. However, DOM in leachate from newer landfill was observed to scavenge available ·OH at a faster rate (8.28 x 109 M-1s-1). The combination of fast rate of reaction with ·OH and abundance of DOM in the sampled leachate severely limited the contribution of ·OH to degradation of an O3- and ·OH-labile organic probe compound (bisphenol-a) in the ozonated mature leachate (f·OH = 0.03). Substantial dosing of both O3 and H2O2 (> 70 mg/L and >24 mg/L, respectively) may be required to see at least 1-log-removal (>90%) of an ·OH-selective leachate contaminant (parachlorobenzoic acid) in a mature landfill leachate. |
