Ecological Engineering and Environment Protection, No 1, 2019, p. 37-53 doi.org/10.32006/eeep.2019.1.3753 This article is distributed under the terms of 37 the Creative Commons Attribution License CLASSICAL AND NEW ASPECTS IN DEGRADATION OF AROMATIC XENOBIOTICS Evgenia K. Vasileva, Tsvetomila I. Parvanova-Mancheva, Venko N. Beschkov Abstract: Organic chemical mixtures are prevalent in waste waters from industrial and municipal sources as well as in contaminated groundwater. Phenols are pollutants found in wastewaters from oil refineries, chemical plants, explosives, resins and coke manufacture, coal conversion, pesticide and textile industries. The main contaminants of refinery wastewater include phenols, polycyclic aromatic hydrocarbons (PAHs) as well as heavy metals. Among these toxic pollutants, phenols are considered to be the most hazardous ones, and they are certainly the most difficult to remove. Phenolic compounds are toxic at relatively low concentration. Because of these low concentrations the most suitable methods for their removal are the microbial ones. The present work is a review of biodegradation of phenol. Degradation of phenol occurs as a result of the activity of a large number of microorganisms including bacteria, fungi and actinomycetes. There are reports on ma33ny microorganisms capable of degrading phenol through the action of variety of enzymes. These enzymes may include oxygenases, hydroxylases, peroxidases, tyrosinases, oxidases etc. Batch experiments were carried out in a different bioreactors. Biodegradation of organic chemicals by microbes using pure cultures can produce toxic intermediates. This problem may be overcome by the use of mixed cultures that have a wider spectrum of metabolite degradation properties. In this revew we described also some new technology for biodegradation of phenol like: different immobilization, FISH (Fluorescence in-situ hybridization) analysis, nanobiotechnologies and etc. Key words: phenol, biodegradation, microorganisms, enzymes, immobilization, FISH analysis, nanobiotechnologies INTRODUCTION Phenol is one of the main pollutants in industrial waste water. Phenol and its vapors are erosive to the respiratory tract, the skin and the eyes. With the development of industrial production and continuous demand for chemicals, a large volume of wastewater containing phenols was discharged into the aquatic environment. Moreover, chemical leakage further increased the emission of phenols into aquatic systems. Phenol and its methylated derivative (cresols) were selected due to their extensive use in industry and ecotoxicity to freshwater and marine organisms. The review from Duana et al. (2018) [1] focused on the ecotoxicity of phenol and m-, o-, and p-cresol on aquatic systems. The mechanism of action of phenols was also discussed. The aim of literature review [1] was to summarise the knowledge of the behaviour, and toxicity on marine and freshwater organisms, of phenols as well as to try to select a series of sensitive biomarkers suitable for ecotoxicological assessment and environmental monitoring in aquatic environments. Phenols are typically classified into two main types on the basis of the number of phenol units, including polyphenols and simple phenols. Phenols are not only synthesized industrially, but also produced by plants and microorganisms [2, 3]. They could accumulate in surface water, ground water and soil when released into the environment [4]. Generally, microorganisms can be applied to water treatment with phenol pollution, such as Pseudomonas sp. and Acinetobacter sp. [5]. Accidental spills of phenol, which happened in the Port of Gothenburg (Sweden) [6] and Xin’an River (China), caused leakage of a significant amounts of phenol, posing a threat to water quality and aquatic systems (China Chemical Safety Association (2011) [7]; HELCOM (2002) [8]). Due to their high water-solubility (phenol, 8.28 g/100 mL; cresols, 2.15–2.60 g/100 mL), phenol and cresols can persist at a high concentration in aquatic environments [9]. BIODEGRADATION STUDIES MECHANISM OF AEROBIC PHENOL DEGRADATION It was investigated detoxification potential and rehabilitation of activated sludge (AS) after shock loading of Sofia’s wastewater treatment plant ‘Kubratovo’ with mazut [10]. The studied enzymological indicators for the detoxification of the aryl-containing contaminants in mazut are the key enzymes of the preparatory pathways of the cleavage of the benzene ring. Parallel to this authors studied the succinate dehydrogenase activity, which is an indicator of the functioning of the cycle of tricarboxylic acids (CTC) on the one hand, and the infusion of the metabolic products of detoxification in the central metabolic pathways, on the other (Fig. 1).