Microbial degradation of lignin, a natural complex biopolymer, a renewable raw material with a wide range of applications, has been mainly directed at fungal systems, nevertheless, recent studies have proposed the bacterial role in lignin degradation and modification since bacteria possess remarkable environmental adaptability, and various production of enzymes and biochemistry. An occurrence of a high proportion of lignin-degrading genes has been confirmed in actinobacteria and proteobacteria classes by bioinformatics analysis, which points to the probability of undiscovered pathways and enzymes. Because of that, bacterial lignin decomposition might be substantially different from fungal lignin decomposition. Bacteria capable of lignin modification and degradation belong to actinomycetes, some Firmicutes, α-proteobacteria, and γ-proteobacteria. The enzymes responsible for lignin degradation are lignin peroxidase, manganese-dependent peroxidase, versatile peroxidase, dye-decolourizing peroxidase, and laccases. One of the main lignin producers is the pulp and paper manufacturing industry. Lignolytic microorganisms have been identified from diverse habitats, such as in plants, soil, wood, and the gut. Bacterial strains Bacillus, Rhodococcus, Sterptomyces, and Pseudomonas have been reported to have lignin decomposition ability. This review aims to describe the role of bacteria in lignin degradation, bacterial species, and bacterial enzymes included in lignin degradation. Several reports about bacterial species involved in lignin degradation are also highlighted, and the current state of the knowledge on the degradation of lignin from the pulp and paper manufacturing industry are reported.

Xenobiotics are compounds of synthetic origin, usually used for domestic, agricultural, and industrial purposes; in the environment, they are present in micropollutant concentrations and high concentrations (using ng/L to µg/L units). Xenobiotics can be categorized according to different criteria, including their nature, uses, physical state, and pathophysiological effects. Their impacts on humans and the environment are non-negligible. Prolonged exposure to even low concentrations may have toxic, mutagenic, or teratogenic effects. Wastewater treatment plants that are ineffective at minimizing the release of xenobiotic compounds are one of the main sources of xenobiotics in the environment (e.g., xenobiotic compounds reach the environment, affecting both humans and animals). In order to minimize the negative impacts, various laws and regulations have been adopted in the EU and across the globe, with an emphasis on xenobiotics removal from the environment, in a way that is economically, environmentally, and socially acceptable, and will not result in their accumulation, or creation of compounds that are more harmful. Detection methods allow detecting even small concentrations of xenobiotics in samples, but the problem is the diversity and mix of compounds present in the environment, in which it is not known what their effects are). In this review, the division of xenobiotics and their detection methods will be presented.

Per- and polyfluoroalkyl substances (PFASs), highly stable synthetic organic compounds with multiple carbon-fluorine bonds, are emerging as environmental contaminants, toxic, bioaccumulative, and environmentally persistent. PFASs are strongly resistant to biological and chemical degradation, and therefore PFASs present a challenge to researchers and scientists for a better understanding and application of remediation methods and biodegradation of PFASs and have become subject to strict government regulations. The review summarizes the recent knowledge of bacterial and fungal degradation of PFASs, as well as the enzymes involved in the processes of transformation/degradation of PFASs.

Biological denitrification is a generally economically viable and reliable technology for nitrate (NO₃⁻-N) and nitrite (NO₂⁻-N) removal from wastewater. Nitrate/nitrite reduction requires an electron donor, which can be supplied from influent wastewater organic compounds, added as an external carbon source, or by endogenous respiration. Decisions regarding the selection of an external carbon source should take into consideration its cost, sludge generation quantity, the rate and efficiency of denitrification, and chemical storage safety. The expense of waste management and external carbon sources accounts for up to 50% of the overall cost of wastewater treatment. The carbon source characteristics required for biological denitrification affect the microbial community structure, denitrification rate, and intermediate products. This review is based on a bibliometric analysis and a systematic literature review providing information and insight into the topic of the denitrification process using different carbon sources. In this review, the main focus was on discussing alternative carbon sources vs. traditional carbon sources in terms of the carbon source price, C/N ratio, denitrification efficiency and rate, operational parameters, and advantages and disadvantages, as well as the limitations in the denitrification process. Future perspectives may include the operating parameters influencing the stability of the removal performance; the maintenance and improvement of nitrate removal; a study of the diversity of the microbial community; research on the application of new alternative carbon sources in denitrification; and N₂O emission detection and minimisation.

The accumulation of organochlorines (OCs) in mussel tissue depends on the physiological and biochemical status of the organism and its interaction with the environment. Mytilus galloprovincialis, 2- and 1-year-old mussels, sampled from Mali Ston Bay, a reference area, and transplanted to Kaštela Bay in cages, were used for the assessment of OC levels and influence of biological parameters on accumulation. Results of bimonthly exposures during one year highlighted that OC accumulation decreases with increasing mussel age. Polychlorinated biphenyls (PCBs) and p,p′-dichlorodiphenyltrichloroethane (p,p′-DDTs) increased, while organochlorine pesticide (OCP; i.e., HCB, lindane, heptachlor, and aldrin) variations were very low. Statistical analysis generally did not confirm the significant effect of lipid content on the accumulation of OCs in mussel tissue. OC levels in mussels were below the maximum permitted levels for human consumption (European Commission).