Challenges and Recent Advances in Enzyme-Mediated Wastewater Remediation-A Review

Abstract

Different classes of artificial pollutants, collectively called emerging pollutants, are detected in various water bodies, including lakes, rivers, and seas. Multiple studies have shown the devastating effects these emerging pollutants can have on human and aquatic life. The main reason for these emerging pollutants in the aquatic environment is their incomplete removal in the existing wastewater treatment plants (WWTPs). Several additional treatments that could potentially supplement existing WWTPs to eliminate these pollutants include a range of physicochemical and biological methods. The use of enzymes, specifically, oxidoreductases, are increasingly being studied for their ability to degrade different classes of organic compounds. These enzymes have been immobilized on different supports to promote their adoption as a cost-effective and recyclable remediation approach. Unfortunately, some of these techniques have shown a negative effect on the enzyme, including denaturation and loss of catalytic activity. This review focuses on the major challenges facing researchers working on the immobilization of peroxidases and the recent progress that has been made in this area. It focuses on four major areas: (1) stability of enzymes upon immobilization, enzyme engineering, and evolution; (2) recyclability and reusability, including immobilization on membranes and solid supports; (3) cost associated with enzyme-based remediation; and (4) scaling-up and bioreactors.

Keywords: enzyme immobilization; hybrid nanoflowers; metal organic framework; peroxidases enzymes; water remediation enzyme evolution.

Figure 1

Potential pathways for emerging pollutants (Eps) to enter drinking water.

Figure 2

Commonly used approaches for enzyme immobilization.

Figure 3

Examples of enzyme immobilization on various solid supports and their applications [95].

Figure 4

Removal of 2,4-dichlorophenol by laccase enzyme immobilization on MOF (Fe₃O₄-NH₂@MIL-101(Cr)) Reprinted from [89] with permission from Elsevier. Copyright © 2021 Elsevier B.V. License Number: 5174580396809.

Figure 5

Methyl orange (MO) dye degradation of by microperoxidase (MP)-8@nanoMIL-101: (a) NanoMIL-101 and the structure of microperoxidase-8, and (b) the degradation rate of MO by MP-8@nanoMIL-101 Reprinted from [130] with permission from John Wiley and Sons. Copyright © 2021 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim. License Number: 5174580612855.

Figure 6

Analysis of degradation of bisphenol A by hNFs, as monitored by HPLC Reprinted from [142] with permission from the American Chemical Society. Copyright © 2021 American Chemical Society.

Figure 7

Some of the commonly used types of bioreactors: (A) fixed bed bioreactors, (B) fluidized bed bioreactors, and (C) stirred tank bioreactors.

Figure 8

Example of a packed bed bioreactor used for dye degradation; (1) dye vessel, (2,4 and 6) flow control valves, (3) substrate vessel, (5) immobilized HRP enzyme, and (6) decolorized product Reprinted from [79] with permission from Elsevier. Copyright © 2021 Elsevier B.V. License Number: 5174590020620.

Figure 9

Diagram of fluidized-bed reactor with laccase enzyme immobilized on Eupergit C Reprinted from [168] with permission from Elsevier. Copyright © 2021 Elsevier B.V. License Number: 5174590199379.