Features of Phenanthrene Transformation by Microbial Complexes of Groundwater in the Riverbank Filtration Zone

Abstract This manuscript examines the microbial transformation of persistent polycyclic aromatic hydrocarbons (PAHs) and their low-molecular-weight representative, phenanthrene, during the interaction of groundwater and river water (RW). Experimental studies have shown that phenanthrene transformation in the riverbank filtration zone occurs at different temperatures (23 and 4°C) and depends on the adaptive potential and physiological characteristics of microbial complexes (MCs). Phenanthrene transformation products are determined with use of spectrophotometry (UV-3600 Shimadzu, Japan) and gas chromatography (Crystal-5000.1, Russia). Maximum microbial activity at 23°C is observed in samples taken from a well, located 50 m from the riverbank in the upper aquifer (AQ). MCs become more active in groundwater in the lower AQ at 4°C. Phenanthrene transformation is accompanied by a change in the color of the experimental fluid and the formation of slimy biofilms. According to the spectral characteristics of phenanthrene transformation products, maximum changes are observed in its aliphatic component of the molecule at a temperature of 23°C with the participation of MCs from the upper AQ, 50 m from the riverbank. The formation of aromatic components during phenanthrene transformation is recorded in the lower layers of the AQ at depths of 35 and 50 m at different distances from the riverbank filtration zone. At a low temperature (4°C), the behavior of groundwater MCs varies depending on the sampling depth and corresponds to the adaptive potential to temperature in situ. The maximum activity of microbial phenanthrene transformation, relative to its aliphatic, aromatic, and chromophore components, is recorded in deeper layers of the AQ (25 and 35 m). Regardless of temperature, toxic organic substances (isopropanol, isobutanol, acetone, hexane, and methylated benzene derivatives) are identified among the phenanthrene transformation products, which can affect the quality of groundwater and create problems in water treatment.