## 6 Types and Mechanisms of Removing Xenobiotics from Water
### Mechanism of Removing Xenobiotics from Water  
There are two types of lactose-catalyzed reactions: catabolic and anabolic. The catabolic pathways involve mediators, i.e., small organic substances that facilitate the course of the redox cycle. In contrast with anabolic processes, catabolic processes are mediated by lacases derived from white or brown wood rot fungi [6,242]. [PERSON] et al. (2013) list two factors that may affect the course of reactions catalyzed by lacase. These are (i) the redox potential of the enzyme and (ii) the stability of the phenoxy radicals formed as a result of oxidation by lacase. Fungal lacases, responsible for catabolic processes and wood decomposition, show a high redox potential compared to lacases involved in anabolic processes [1,9]. As a result of the decomposition of the lignin present in wood, phenols are formed, e.g., syringaldehyde and acetosyringone, which are characterized by high structural stability and a long half-life of the corresponding radicals. The listed properties of the products resulting from the decomposition of wood by lacase shift the course of the reaction toward catabolic processes [6]. The bioremediation and detoxification of xenobiotics present in the environment is an example of the use of lacase's ability to catalyze both catabolic and anabolic reactions (Figure 4) [6,242,243]. Synthetic dyes are high molecular organic compounds with complex structures. For the decolorization of thiazole yellow G, [PERSON] et al. (2019) used the filamentous fungus _Aspergillus niger_ LAG [244]. A significant role in the degradation of this dye was attributed to lacase. The fungus showed significant induction of lacase (71%) and lignin peroxidase (48%) in the presence of xenobiotics. The scheme of the dye decomposition is likely as follows: (i) lignin peroxidase catalyzes asymmetric cleavage of the bond in thiazole yellow G, two sodium 6-methyl-2-phenyl-1,3-benzothazole-7-sulphate molecules are formed, and (ii) sodium 6-methyl-2-phenyl-1,3-benzothiazole-7-sulphate molecules are desulfonated and demethylated by lacase, resulting in 2-phenyl-4,5-dihydro-1,3-thiazole. These products showed less toxic potential. As mentioned earlier, polymerization reactions resulting from oxidative coupling are also involved in the removal of organic pollutants. These processes lead to the formation of adducts or copolymer products that are insoluble in aqueous environments. To remove pollutants that polymerize, the wastewater is then filtered or sedimented [243; 245]. [PERSON] et al. (2019) proved that the way to remove triclosan, a compound with antibacterial properties, which is resistant to biodegradation [246; 247; 248], from water is the enzymatic activity of the _T. versicolor_ increase supported by Cu\({}^{2+}\) ions [137], in which mainly triclosan dimers, trimers and tetramers are produced. A possible transformation mechanism of the xenobiotic was proposed: (i) lactose catalyzes the oxidation of triclosan to produce intermediate phenoxy radicals, and (ii) phenoxy radicals link together via C-C and C-O-C radical covalent bonds, forming mainly oligomers. The introduction of Cu\({}^{2+}\) to the reaction environment was probably the reason for the increase in the activity and stability of the enzyme and the intensification of the self-polymerization of triclosan by the formation of more triclosan oligomers. Acetaminophen is one of the difficult-to-remove types of pharmaceutical contaminants that have been noticed in municipal water. [PERSON] et al. (2018) presented a potential method of removing acetaminophen from water based on the lactose-catalyzed oxidative coupling reaction with the formation of insoluble products that are easily separated from the liquid by filtration [249]. In order to increase the efficiency of xenobiotic removal, a strategy of double pH optimization was used (enzyme solution at pH 7.4 was added to substrate solution at pH 4.2).