Aptitude of Oxidative Enzymes for Treatment of Wastewater Pollutants: A Laccase Perspective

Abstract

Natural water sources are very often contaminated by municipal wastewater discharges which contain either of xenobiotic pollutants and their sometimes more toxic degradation products, or both, which frustrates the universal millenium development goal of provision of the relatively scarce pristine freshwater to water-scarce and -stressed communities, in order to augment their socioeconomic well-being. Seeing that both regulatory measures, as regards the discharge limits of wastewater, and the query for efficient treatment methods remain unanswered, partially, the prospects of enzymatic treatment of wastewater is advisable. Therefore, a reconsideration was assigned to the possible capacity of oxidative enzymes and the respective challenges encountered during their applications in wastewater treatment, and ultimately, the prospects of laccase, a polyphenol oxidase that oxidizes aromatic and inorganic substrates with electron-donating groups in treatment aromatic contaminants of wastewater, in real wastewater situations, since it is assumed to be a vehicle for a greener community. Furthermore, the importance of laccase-driven catalysis toward maintaining mass-energy balance, hence minimizing environmental waste, was comprehensibly elucidated, as well the strategic positioning of laccase in a model wastewater treatment facility for effective treatment of wastewater contaminants.

Keywords: environomics; laccase; oxidative enzymes; wastewater pollutants; wastewater treatment.

Figure 1

The hypothetical cross-linking of the fruit monomeric sugars, glucose and fructose to form the dimer sucrose or invert sugar.

Figure 2

The characteristic disintegration of lignocellulosic polymers to liberate simpler carbon sources for bacterial metabolism and the consequent formation of humus from recalcitrant plant lignin residues and furfural. The left portion of the partition highlights the importance of hydrolytic enzymes in ensuring nutrient availability to the denizen bacteria, while the right portion summarises the mechanistic insight of humus formation.

Figure 3

Hypothetical degradation of the insecticide, lindane, and its pathway to the production of organic acids. The colour tint on the rings represents the gradual metamorophosis from recaltrance and toxicity to biodegradability and eco-friendliness.

Figure 4

Laccase oxidative transformation of some hospital wastewater pollutants.

Figure 5

The polymerization of phenolic radicals generated from xenobiotics degradation.

Figure 6

Schematic of a typical conventional wastewater treatment process showing the prospective strategic position of laccase treatment. The laccase immobilization chamber comprises a pretreated lignocellulosic support, which possesses antimicrobial properties. The location of the chamber helps to reduce or totally eliminate aromatic pollutants that could interfere with the efficiency of the flocculation step.