Halogenated phenols appear in many aspects of our lives as they are used for wood preservation, as pesticides, flame retardants, and even in computers. They are toxic, bio-accumulative and bio-retardant. However, horseradish peroxidase has been shown to be useful for polymerizing and dehalogenating them, thus reducing their toxicity. In the presence of hydrogen peroxide, HRP rapidly polymerizes phenols in aqueous solution with high selectivity. A novel glass-based support incorporating titanium dioxide for immobilizing the enzyme was developed and characterized (Tglass). Under UV irradiation it was shown to reduce the blockage of the enzyme active sites by the polymerized product and also to provide in situ production of H2O2 with little inactivation of the enzyme. A packed bed reactor that utilized the immobilized HRP to treat 4-bromophenol (as model substrate) under UVB irradiation was shown to give 75% reduction of 4-bromophenol, 21% reduction in total organic carbon and formation of 70 µM bromide over 16 hours operation. The reactor was tested on reservoir water spiked with pentabromophenol and pentachlorophenol. The system was able to transform 98% of these halogenated phenols and to release 70% of their halogen content. Pentachlorophenol (PCP) and/or pentabromophenol (PBP) spiked into a sample of drinking water (8 and 10 mg L-1, respectively) was treated by the HRP-Tglass packed bed reactor under UVB radiation. The treatment gave 98% transformation for both species and up to 4 of the 5 available halogens (bromide and chloride) were removed. Toxicity tests were performed on a solution feed containing PCP and/or PBP in MilliQ water (1 mg L-1) before and after treatment. The toxicity (as measured by Microtox®) of the treated effluent showed that after treatment the lethal toxicity (LD50) was removed while the effect toxicity (EC50) has reduced. Toxicity tests using Hydra hexactinella showed a slight decrease in toxicity, however the dehalogenated PCP and PBP mixture was shown to have a greater decrease in toxicity. Dehalogenation plays an important rule in reduction in toxicity; it was found that for a partial transformation (up to 70% in both species) of the PBP and PCP mixture (0.67 and 0.89 mg L-1) in reservoir water, an increase in toxicity occurs. The results of the present work clearly show the potential for continuous removal of soluble phenolic pollutants from water and wastewater streams by immobilized horseradish peroxidase using the novel Tglass developed in this study.
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