Lignin peroxidase‐catalyzed polymerization and detoxification of toxic halogenated phenols

Abstract

Halogenated phenols and bisphenols are recognized as being recalcitrant in conventional biological treatments. The current research evaluated lignin peroxidase-catalyzed oxidation and polymerization as a potential alternative for their detoxification. Gel permeation-HPLC analysis demonstrated the formation of dimers, trimers and tetramers upon oxidation of the target substrates. Polymerization was accompanied by effective detoxification of the aqueous phase during oxidation of 2,4-dibromophenol, the extent of which correlated with the extent of oxidation and polymerization. Steady state kinetic measurements at a saturating concentration of H 2 O 2 revealed high K m values (270-1100 µmol dm −3 ) for the target substrates, reflecting the strong electron-withdrawing properties of halogen substituents, which increase the oxidation potential of the phenols, resulting in thermodynamically less favorable reactions. However, k cat values were not dissimilar from non-halogenated phenols and the rapid oxidation and polymerization suggests that low retention times could be expected in a continuous process for their treatment, in contrast to conventional biological methods. The operational stability of lignin peroxidase was significantly improved by inclusion of redox mediators, which resulted in enhanced oxidation and more rapid reaction rates. However, due to their inherent toxicity, the use of redox mediators impeded toxicity assays. The findings highlight the potential of lignin peroxidase as a possible alternative for the high-rate treatment of industrial wastewater when conventional methods are ineffective.

Linking Enzymatic Oxidative Degradation of Lignin to Organics Detoxification

“…Dimers, trimers, and tetramers are found in LiP-treated reactions containing these chemicals [ 107 ]. Through polymerization, the phenolic compounds decrease their reactivity and solubility and tend to precipitate, thereby alleviating the toxicity [ 108 ]. It is also often noted that phenolic pollutants can be completely mineralized by the LiP-producing microorganisms, suggesting that other enzymes in addition to LiP are involved [ 109 ].…”

“…LiP has been used in treating paper mill waste and also in detoxifying delignified feedstock for biorefineries [ 110 ], halogenated phenol toxics [ 108 ], and endocrine-disrupting pollutants ( p – t -octylphenol, bisphenol A, estrone, 17 β-estradiol, and ethinylestradiol, which all have phenolic hydroxyls) [ 111 ]. Decolorization of synthetic dyes is also reported.…”

Characterization of biomass and its derived char using13C-solid state nuclear magnetic resonance

“…13 C- 13 [ 43,44] Lignin can be further processed to obtain important phenol-derived chemicals used in various chemical industries. [45,46] This section shows several well-known biomass-based carbons for which 13 C MAS ssNMR has provided an extremely valuable contribution to their structural analysis. Examples focus on lignin and cellulose, both being C-rich natural biopolymers, and their related amorphous chars, obtained from their pyrolytic and chemical/physical treatment.…”

Monitoring the laccase reaction of vanillin and poplar hydrolysate

“…In the case of laccase reaction, however, phenolics are the substrates as well as the products (often polyphenols). Moreover, measurement of the laccase reaction is even more complicated since the polymerized phenolic product is often insoluble and precipitates …”