Removal of benzidine from polluted water by soluble and immobilized peroxidase in batch processes and continuous horizontal bed reactor

Role of functional groups in the production of self-assembled microfibrillated cellulose hybrid frameworks and influence on separation mechanisms of dye from aqueous medium

In this article, the role of surface ζ-potential, surface charge density of functional groups and available surface functional groups (-OH and -COO^-) of microfibrillated cellulose (MFC) was explored in the production of self-assembled dimensional frameworks. Furthermore, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) oxidation of MFC and in situ TEMPO functionalization of produced frameworks were performed. The effect of increased charge density of carboxylic groups (-COO^-) and decrease in surface ζ-potential on binding of titanium dioxide (TiO₂) and horseradish peroxidase (HRP) was investigated further. High binding of TiO₂ and HRP was reported due to high density of carboxylic group (-COO-) on produced functional frameworks. Thereafter, a model water of Irgalite Violet NZ dye was targeted to understand the behavior of available functional groups and introduced surface ζ-potential of frameworks towards adsorption of dye. Possible size-exclusion of dye aggregates was also explored using neat-MFC frameworks. Photo-oxidation (TiO₂) and enzymatic catalysis (HRP) were studied further and highly effective system towards dye degradation was reported. Lastly, this study has shown a well deliberated quantitative understanding of functional groups/their density responsible for the production of frameworks and separation of dye.

A combination of absorption and enzymatic biodegradation: phenol elimination from aqueous and organic phase

Peroxidase from Brassica rapa was immobilized as cross-linked enzyme aggregates (CLEAs) and used to treat air containing phenol as a model molecule of volatile organic compounds (VOCs). Prior to an enzymatic treatment, phenol was absorbed into an aqueous or organic phase (silicone oil) to reach concentrations ranging from 20 to 160 mg/L. The process was carried out by introducing a desired weighing of BRP-CLEAs into preparations and reaction was started by injecting H₂O₂ solution to the medium. Optimization of the reaction conditions in the organic solvent revealed an optimal contact time of 60 min, 60 mg/L of phenol concentration and 3 mM H₂O₂, leading to a maximum removal yield of 70% for 3.4 UI/mL of BRP-CLEAs. These results were compared to those obtained in an aqueous medium that showed 90% of degradation yield after 40 min in the following conditions, 90 mg/L of initial phenol amount, 2 mM of H₂O₂ and 2.5 UI/mL of BRP-CLEAs. Parameters of the Michaelis-Menten model, Km and Vmax, were also determined for the reaction in both phases. Phenol removal by BRP-CLEAs in silicone oil succeeded with 70% of conversion yield. It is promising regarding the transposition of such enzymatic process to hydrophobic VOCs.

Applications of soluble, encapsulated and cross-linked peroxidases from Sapindus mukorossi for the removal of phenolic compounds

Peroxidases have been known to polymerize phenolic compounds and precipitate them from solution. Sapindus peroxidases (SPases) were extracted from the leaves of Sapindus mukorossi and precipitated with four volumes of chilled methanol. Soluble, encapsulated and cross-linked forms of enzymes were used for the removal of phenolic compounds (initial concentration 1.0 mM) in a stirred batch reactor. Calcium alginate beads were prepared using sodium alginate and calcium chloride at 1.5% and 5.0% (w/v), respectively. Sodium alginate and glutaraldehyde at 1.0% (w/v) and 0.8% (v/v), respectively, were optimized for cross-linking of SPases. The maximal removal of 2-chlorophenol was found in the buffers ofpH range 4-7 and at 30-60 degrees C in the presence of 1.2 mM H2O2 by soluble enzymes, but encapsulated and cross-linked enzymes worked well at pH 5 and at 50 degrees C in the presence of 0.8 mM H2O2. The optimized doses of soluble, encapsulated and cross-linked SPases were 1.2, 4.2 and 1.2 mg/mL, respectively, for the removal of phenolic compounds. Encapsulated and cross-linked enzymes showed a lower efficiency than soluble enzyme but can be reused in multiple cycles for the removal of phenolic compounds.