No abstract

Bio-based and cost effective method for phenolic compounds removal using cross-linked enzyme aggregates

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 HO 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 HO, 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 HO 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.

This study proposes a new technique to treat waste air containing 2-Chlorophenol (2-CP), namely an integrated process coupling absorption of the compound in an organic liquid phase and its enzymatic degradation. Silicone oil (47V20) was used as an organic absorbent to allow the volatile organic compound (VOC) transfer from the gas phase to the liquid phase followed by its degradation by means of Cross-linked Brassica rapa peroxidase (BRP) contained in the organic phase. An evaluation of silicone oil (47V20) absorption capacity towards 2-CP was first accomplished by determining its partition coefficient (H) in this solvent. The air-oil partition coefficient of 2-CP was found equal to 0.136 Pa m(3) mol(-1), which is five times lower than the air-water value (0.619 Pam(3) mol(-1)). The absorbed 2-CP was then subject to enzymatic degradation by cross-linked BRP aggregates (BRP-CLEAs). The degradation step was affected by four parameters (contact time; 2-CP, hydrogen peroxide and enzyme concentrations), which were optimized in order to obtain the highest conversion yield. A maximal conversion yield of 69% and a rate of 1.58 mg L(-1) min(-1)were obtained for 100 min duration time when 2-CP and hydrogen peroxide concentrations were respectively 80 mg L(-1) and 6 mM in the presence of 2.66 UI mL(-1) BRP-CLEAs. The reusability of BRP-CLEAs in silicone oil was assessed, showing promising results since 59% of their initial efficiency remained after three batches.

In the present study, absorption in an organic solvent followed by enzymatic biodegradation by cross‐linked peroxidase from Brassica rapa (BRP‐CLEAs) was successfully applied as a solution for toluene removal from waste‐air in batch experiments. Silicone oil (PDMS 47V20) showed a high capacity for toluene absorption, regarding its air‐PDMS partition coefficient (2.08 Pa m3 mol−1) when compared to air‐water (666 Pa m3 mol−1). Box–Behnken restricted duplicate design was employed for the optimization of the enzymatic degradation of toluene in PDMS. Effects of four independent variables, namely, BRP‐CLEAs activity, toluene and hydrogen peroxide concentrations and sonication, were studied by choosing two responses: conversion yield and initial rate of reaction. Analysis of the results showed that both hydrogen peroxide and toluene concentrations presented the largest effect on the process while sonication had no effect. On the other hand, the coefficient of determination R2 and the adjusted R2 were 0.828 and 0.770 for conversion and 0.919 and 0.911 for initial rate, respectively. The optimum conversion determined was 60% of toluene removal.