Biological disposal of hazardous waste

Enhanced removal of phenol from biorefinery wastewater treatment using enzymatic and Fenton process

The valorisation of biomass has been commonly carried out in biorefineries. The environmental concerns about these processes have not been intensely considered, demanding further investigations. Particularly, phenols are founded in high concentrations in biorefinery wastewater and are considered compounds of major concern. In this study, we evaluated the bioconversion of phenols by enzymatic treatment using the enzyme Horseradish peroxidase (HRP) and the Fenton process. The results showed an enzymatic phenol conversion of 97.5% at pH 7.0, enzyme activity of 0.8 U/mL and hydrogen peroxide concentration of 1.61 g/L. So as to enhance the treatment, we evaluate the Fenton reaction as a complementary process for further remaining phenol conversion. The best conditions for Fenton process were achieved using a hydrogen peroxide concentration and [H₂O₂]:[Fe] ratio of 3.90 g/L and 74, respectively, and the obtained phenol concentration in the treated wastewater was 0.11 mg/L. Chromatography analysis showed that 2-methoxyphenol was the majority compound in the original wastewater, which was subsequently precipitated by the enzymatic treatment. Furthermore, many physicochemical parameters were modified due to the treatment, such as biochemical oxygen demand, chemical oxygen demand and total organic carbon, with removal efficiencies of around 97, 49 and 46%, respectively. HRP combined with Fenton can be considered as an alternative methodology for the biorefinery wastewater treatment, especially regarding the phenols conversion.

Immobilization of laccase from Aspergillus oryzae on graphene nanosheets

Laccase enzymes of Aspergillus oryzae were immobilized on graphene nanosheets by physical adsorption and covalent bonding. Morphological features of the graphene sheets were characterized via microscopy techniques. The immobilization by adsorption was carried out through contact between graphene and solution of laccase enzyme dissolved in deionized water. The adsorption process followed a Freundlich model, showing no tendency to saturation within the range of values used. The process of immobilization by covalent bonding was carried out by nitration of graphene, followed by reduction of sodium borohydride and crosslinking with glutaraldehyde. The process of immobilization by both techniques increased the pH range of activity of the laccase enzyme compared to the free enzyme and increased its operating temperature. On operational stability, the enzyme quickly loses its activity after the second reaction cycle when immobilized via physical adsorption, while the technique by covalent bonding retained around 80% activity after six cycles.

Substrate specificity and enzyme recycling using chitosan immobilized laccase

The immobilization of laccase (Aspergillus sp.) on chitosan by cross-linking and its application in bioconversion of phenolic compounds in batch reactors were studied. Investigation was performed using laccase immobilized via chemical cross-linking due to the higher enzymatic operational stability of this method as compared to immobilization via physical adsorption. To assess the influence of different substrate functional groups on the enzyme's catalytic efficiency, substrate specificity was investigated using chitosan-immobilized laccase and eighteen different phenol derivatives. It was observed that 4-nitrophenol was not oxidized, while 2,5-xylenol, 2,6-xylenol, 2,3,5-trimethylphenol, syringaldazine, 2,6-dimetoxyphenol and ethylphenol showed reaction yields up 90% at 40 °C. The kinetic of process, enzyme recyclability and operational stability were studied. In batch reactors, it was not possible to reuse the enzyme when it was applied to syringaldazne bioconversion. However, when the enzyme was applied to bioconversion of 2,6-DMP, the activity was stable for eight reaction batches.

Modeling the adsorption kinetics of some priority organic pollutants in water from diffusion and activation energy parameters

The kinetic aspects of adsorption of some priority organic pollutants, viz., phenol (hydroxybenzene), o-hydroxyphenol (1,2-dihydroxybenzene), m-hydroxyphenol (1,3-dihydroxybenzene), and 4-nitrophenol (1-hydroxy-4-nitrobenzene), on fly ash have been studied. The process is found to be of complex nature consisting of both surface adsorption and pore diffusion, the extent being estimated from the diffusion coefficient value. Activation parameter data for the ultimate adsorption as well as the pore diffusion are also evaluated. The data indicate that in the studied solute concentration range, external transport mainly governs the rate-limiting process.

The influence of increasing chlorine content on the accumulation and metabolism of polychlorinated biphenyls (PCBs) by Paul's Scarlet Rose cells

Four radiolabled congeners of biphenyls with increasing chlorine content (biphenyl; 1-monochlorobiphenyl; 2,2',4,4'-tetrachlorobiphenyl; and 2,2',4,4',5,5'-hexachlorobiphenyl) were provided to suspension cultures of rose (Rosa sp. cv. Paul's Scarlet) for 4 days. Both the kinetics of (14)C exchange between the cells and medium, and the metabolism of the parent compounds depended on the chlorine content of the congeners. Analysis of both the cells and their medium showed that of the recovered radioactivity 88%, 86%, and 3% of the biphenyl, 1-PCB, and 2,2',4,4'-PCB were metabolized respectively to polar and insoluble residue products. The 2,2',4,4',5,5'-PCB did not appear to be metabolized.

Oxidation of persistent environmental pollutants by a white rot fungus

The white rot fungus Phanerochaete chrysosporium degraded DDT [1,1,-bis(4-chlorophenyl)-2,2,2-trichloroethane], 3,4,3',4'-tetrachlorobiphenyl, 2,4,5,2',-4',5'-hexachlorobiphenyl, 2,3,7,8-tetrachlorodibenzo-p-dioxin, lindane (1,2,3,4,5,6-hexachlorocylohexane), and benzo[a]pyrene to carbon dioxide. Model studies, based on the use of DDT, suggest that the ability of Phanerochaete chrysosporium to metabolize these compounds is dependent on the extracellular lignin-degrading enzyme system of this fungus.