The influence of different soil constituents on the reaction kinetics of wet oxidation of the creosote compound quinoline

Creosote contaminated sites have become a widespread problem in industriali zed countries. Recently, wet oxidation using high temperature, pressure, wa ter and oxygen followed by activated sludge treatment proved to be an effic ient method for removing a wide selection of creosote compounds in contamin ated soils. Wet oxidation of the creosote compound quinoline was carried ou t in the presence of montmorillionite, quartz and humic acid. The products derived from wet oxidation were identified and treated biologically by acti vated sludge testing their biodegradability. The influence on the oxidation kinetics, of quinoline during wet oxidation was pH dependent. Humic acid s upported the oxidation of quinoline, whereas the addition of montmorillioni te and quartz had either an inhibiting effect or led only to a slight incre ase in oxidation. In mixtures of soil constituents, especially at low conte nts of humic acid, the adsorption of quinoline on montmorillionite prevente d oxidation at neutral pH. Thus, alkaline extraction of both quinoline and humic acid was needed for an efficient oxidation. A proposed reaction mecha nism suggests that quinoline was oxidized by hydroxyl radicals formed durin g the oxidation of the humic acid. A wide selection of reaction products (m ainly carboxylic acids, benzene and pyridine derivatives) derived from the wet oxidation of humic acid and quinoline. The reaction products from humic acid degradation had a rate limiting effect on the wet oxidation of quinol ine leaving small residues of quinoline after the treatment. On the contrar y, these reaction products also improved the biodegradation of products fro m the quinoline oxidation due to co-digestion of carboxylic acids. Therefor e, the presence of soil components (mainly humic acid) improved the combine d wet oxidation and biological activated sludge treatment of quinoline. (C) 2001 Elsevier Science B.V. All rights reserved.