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Degradation of pentachlorophenol by a novel peroxidase-catalyzed process in the presence of reduced nicotinamide adenine dinucleotide

Li, Haitao, Li, Yuping, Cao, Hongbin, Li, Xingang, Zhang, Yi
Chemosphere 2011 v.83 no.2 pp. 124-130
NAD (coenzyme), catalase, electron paramagnetic resonance spectroscopy, gas chromatography, hydroxyl radicals, mass spectrometry, oxidation, pH, pentachlorophenol, peroxidase, polymerization, superoxide anion, superoxide dismutase, toxicity
A novel horseradish peroxidase (HRP)-catalyzed H₂O₂ process in the presence of reduced nicotinamide adenine dinucleotide (NADH) was applied to remove aqueous pentachlorophenol (PCP). Parameters (pH, H₂O₂ concentration, HRP activity and NADH dosage) on PCP removal were investigated. It was found that initial 0.05mM PCP was removed by 98% in HRP–NADH–H₂O₂ system at pH 5.0 and 30°C for 1h. Addition of O₂ in HRP–NADH–H₂O₂ system enhanced the removal rate of PCP due to promoting hydroxyl radicals (OH) and superoxide anion radical (O₂ ⁻) generation, which were confirmed by electron paramagnetic resonance (EPR)-spin trapping method. PCP removal efficiency decreased when O₂ ⁻ and H₂O₂ were scavenged by superoxide dismutase and catalase in HRP–NADH–O₂ system, indicating that OH/O₂ ⁻ played a great role in the degradation of PCP. Gas chromatography–mass spectrometry (GC–MS) analysis revealed that octachlorinated dibenzodioxin (OCDD) in residual solution was reduced after treated by the HRP–NADH–O₂ process, resulting in lower toxicity of treated solution than conventional enzymatic process. Two enzymatic-catalysis pathways were proposed for PCP removal in HRP–NADH–H₂O₂/O₂ system: (i) OH/O₂ ⁻ free radical oxidation (ii) conventional phenoxy polymerization.