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Ionic polymer-coated laccase with high activity and enhanced stability: application in the decolourisation of water containing AO7.

Zhang X, Hua M, Lv L, Pan B - Sci Rep (2015)

Bottom Line: The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity.Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7.The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, P.R. China.

ABSTRACT
Eliminating dyes in environmental water purification remains a formidable challenge. Laccase is a unique, environmentally friendly and efficient biocatalyst that can degrade pollutants. However, the use of laccase for the degradation of pollutants is considerably limited by its susceptibility to environmental changes and its poor reusability. We fabricated a novel biocatalyst (LacPG) by coating polyethylenimine onto the native laccase (Lac) followed by crosslinking with glutaraldehyde. The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity. Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7. LacPG was separated from the AO7 solution using an ultrafiltration unit. The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling. LacPG exhibited enhanced stability, high catalytic activity and favourable properties for membrane separation; therefore, LacPG could be continuously reused in an enzymatic membrane reactor with a high efficiency for decolourising water containing AO7. The developed strategy appears to be promising for enhancing the applicability of laccase in practical water treatment.

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Flux change of ultrafiltration membrane (MWCO = 30 kDa) for deionised water, Lac and LacPG (25°C, pressure = 0.1 MPa); error bars shows standard deviations from triplicate measurements.
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f6: Flux change of ultrafiltration membrane (MWCO = 30 kDa) for deionised water, Lac and LacPG (25°C, pressure = 0.1 MPa); error bars shows standard deviations from triplicate measurements.

Mentions: An enzymatic membrane reactor was designed to recycle the enzyme for the decolourisation of the AO7 solution (see Supplementary Fig. S6). Supplementary Figure S7 shows that more than 99% of the LacPG or Lac was rejected by the ultrafiltration polyethersulphone (PES) membrane with a nominal molecular weight cut-off (MWCO) of 30 kDa. Using membranes with MWCOs of 50 kDa and 100 kDa resulted in a significant decrease in the Lac rejection rate to ca. 92% and ca. 12%, respectively, whereas that for LacPG remained at ca. 99% and ca. 95%, respectively. It is reasonable because of the increased size of LacPG relative to Lac as shown in Fig. 1. Prior to performing the decolourisation assay, the performances of Lac and LacPG on membrane fouling were examined because membrane fouling is one of the major obstacles in maintaining efficient performance of an ultrafiltration membrane43. Figure 6 shows the permeate flux that was recorded for the membrane with a MWCO of 30 kDa under a constant pressure of 0.1 MPa. The deionised water flux was constant at ca. 92 L·m−2·h−1 (LMH). The deionised water flux initially decreased significantly over 20 min for Lac and over 80 min for LacPG. Compared with the flux of deionised water, the initial LacPG flux decreased slightly to ca. 89 LMH and that for Lac decreased to ca. 54 LMH. The LacPG flux at the end of the experiment (ca. 67 LMH) suggested that the membrane was moderately fouled. In contrast, severe membrane fouling was observed using Lac (the Lac flux decreased to ca. 10 LMH).


Ionic polymer-coated laccase with high activity and enhanced stability: application in the decolourisation of water containing AO7.

Zhang X, Hua M, Lv L, Pan B - Sci Rep (2015)

Flux change of ultrafiltration membrane (MWCO = 30 kDa) for deionised water, Lac and LacPG (25°C, pressure = 0.1 MPa); error bars shows standard deviations from triplicate measurements.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4317704&req=5

f6: Flux change of ultrafiltration membrane (MWCO = 30 kDa) for deionised water, Lac and LacPG (25°C, pressure = 0.1 MPa); error bars shows standard deviations from triplicate measurements.
Mentions: An enzymatic membrane reactor was designed to recycle the enzyme for the decolourisation of the AO7 solution (see Supplementary Fig. S6). Supplementary Figure S7 shows that more than 99% of the LacPG or Lac was rejected by the ultrafiltration polyethersulphone (PES) membrane with a nominal molecular weight cut-off (MWCO) of 30 kDa. Using membranes with MWCOs of 50 kDa and 100 kDa resulted in a significant decrease in the Lac rejection rate to ca. 92% and ca. 12%, respectively, whereas that for LacPG remained at ca. 99% and ca. 95%, respectively. It is reasonable because of the increased size of LacPG relative to Lac as shown in Fig. 1. Prior to performing the decolourisation assay, the performances of Lac and LacPG on membrane fouling were examined because membrane fouling is one of the major obstacles in maintaining efficient performance of an ultrafiltration membrane43. Figure 6 shows the permeate flux that was recorded for the membrane with a MWCO of 30 kDa under a constant pressure of 0.1 MPa. The deionised water flux was constant at ca. 92 L·m−2·h−1 (LMH). The deionised water flux initially decreased significantly over 20 min for Lac and over 80 min for LacPG. Compared with the flux of deionised water, the initial LacPG flux decreased slightly to ca. 89 LMH and that for Lac decreased to ca. 54 LMH. The LacPG flux at the end of the experiment (ca. 67 LMH) suggested that the membrane was moderately fouled. In contrast, severe membrane fouling was observed using Lac (the Lac flux decreased to ca. 10 LMH).

Bottom Line: The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity.Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7.The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, P.R. China.

ABSTRACT
Eliminating dyes in environmental water purification remains a formidable challenge. Laccase is a unique, environmentally friendly and efficient biocatalyst that can degrade pollutants. However, the use of laccase for the degradation of pollutants is considerably limited by its susceptibility to environmental changes and its poor reusability. We fabricated a novel biocatalyst (LacPG) by coating polyethylenimine onto the native laccase (Lac) followed by crosslinking with glutaraldehyde. The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity. Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7. LacPG was separated from the AO7 solution using an ultrafiltration unit. The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling. LacPG exhibited enhanced stability, high catalytic activity and favourable properties for membrane separation; therefore, LacPG could be continuously reused in an enzymatic membrane reactor with a high efficiency for decolourising water containing AO7. The developed strategy appears to be promising for enhancing the applicability of laccase in practical water treatment.

Show MeSH
Related in: MedlinePlus