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

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 0.05 mM PCP was removed by 98% in HRP–NADH–H2O2 system at pH 5.0 and 30 °C for 1 h. 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.

Research highlights
► A novel peroxidase-coenzyme-catalyzed H2O2/O2 process for removing pentachlorophenol (PCP). It shows higher PCP removal and lower residual toxicity than bare peroxidase process. Coenzyme NADH initiates superoxide anion/hydroxyl radicals in enzymatic process. O2 can increase hydroxyl radical generation and PCP removal. PCP removal is attributed to either phenoxy polymerization or free radical oxidation.