Hydroxyl radical (•OH) scavenging in young and mature landfill leachates

The final discharge point for collected landfill leachates is frequently the local municipal wastewater treatment facility. The salinity, color, nutrient, and anthropogenic 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 (center dot OH). Without a quantitative assessment of total center dot 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, and age of landfill, were characterized for center dot OH-scavenging using an established competition kinetics method. After stripping the samples of inorganic carbon, the DOM in leachate from mature (stabilized) landfill was found to react with center dot OH at a rate of 9.76 x 10 (8) M(-1)s(-1). However, DOM in leachate from newer landfill was observed to scavenge available center dot OH at a faster rate (8.28 x 10(9) M-1s-1). The combination of fast rate of reaction with center dot OH and abundance of DOM in the sampled leachate severely limited the contribution of center dot OH to degradation of an O-3- and center dot OH-labile organic probe compound (bisphenol-a) in oxidized mature leachate (f(OH) = 0.03). Substantial dosing of both O-3 and H2O2 (>70 mg/L and >24 mg/L, respectively) may be required to see at least 1-log-removal (>90%) of an center dot OH-selective leachate contaminant (i.e., parachlorobenzoic acid) in a mature landfill leachate. (C) 2014 Elsevier Ltd. All rights reserved.