Treatment of organic contaminants from water using an integrated sorption-oxidation system
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In-situ treatment of chlorophenols using a permeable reactive barrier is still an emerging research area. A novel integrated sorption-oxidation barrier is proposed and systematically investigated in a neutral pH, very poorly buffered water. Intermittent injections of permanganate oxidise dissolved and sorbed chlorophenol as well as the woody sorbent with manganese dioxide formed as a by-product. Common woody biomass (pine/hardwood) were evaluated as a cost effective sorbent. Chlorophenol uptake on these was relatively low (3–8 mg g-1) with evidence of sorption hysteresis. Increased sorbent particle size and reactions with the oxidant did not significantly affect sorption. Under dynamic conditions non-equilibrium sorption occurred with higher flow rates. Oxidation within the porous media was complex with multiple oxidation processes occurring simultaneously. An analytical method was developed to allow the quantification of chlorophenol in the presence of a quenching agent. This allowed the collection of kinetic data for the permanganate oxidation reaction. Oxidation of dissolved chlorophenol by manganese dioxide was found to be minimal. Early time data showed that the oxidation rate of pine (0.06 min-1) was less than for chlorophenol sorbed on pine (0.07–0.12 min-1) which was much less than for dissolved chlorophenols (0.4–1.48 min-1). This suggests that the reaction between permanganate and pine materials is kinetically controlled and will dominate only after the oxidation reaction with chlorophenol. The rate of sorbed chlorophenol oxidation decreased with increasing contaminant hydrophobicity. In column studies the oxidation of the pine sorbent was found to be both pH and residence time dependent. Some evidence of sorbent/column plugging and reduced sorbent oxidant demand due to manganese dioxide precipitation was found at pH 6.15 but not at pH 2. The research has shown that a novel sorbent-oxidation barrier system that can treat chlorophenol contaminated water is technically feasible. Insights into the key mechanisms that would occur in the system have been given. Further work into operationalizing these processes is still needed.
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